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Purpose: Atezolizumab [anti–programmed death-ligand 1 (anti-PD-L1)] is well tolerated and efficacious in multiple cancers, but has not been previously evaluated in metastatic castration-resistant prostate cancer (mCRPC). This study examined the safety, efficacy, and biomarkers of atezolizumab monotherapy for mCRPC. Patients and Methods: This phase Ia, open-label, dose-escalation and dose-expansion study (PCD4989g) enrolled patients with mCRPC who had progressed on sipuleucel-T or enzalutamide. Atezolizumab was given intravenously every 3 weeks until confirmed disease progression or loss of clinical benefit. Prespecified endpoints included safety, efficacy, biomarker analyses, and radiographic assessments. Results: All 35 evaluable patients [median age, 68 years (range, 45–83 years)] received atezolizumab after ≥1 prior line of therapy; 62.9% of patients had received ≥3 prior lines. Treatment-related adverse events occurred in 21 patients (60.0%), with no deaths. One patient had a confirmed partial response (PR) per RECIST 1.1, and 1 patient had a PR per immune-related response criteria. The confirmed 50% PSA response rate was 8.6% (3 patients). Median overall survival (OS) was 14.7 months [95% confidence interval (CI): 5.9–not evaluable], with a 1-year OS rate of 52.3% (95% CI: 34–70); 2-year OS was 35.9% (95% CI: 13–59). Median follow-up was 13.0 months (range, 1.2–28.1 months). Biomarker analyses showed that atezolizumab activated immune responses; however, a composite biomarker failed to reveal consistent correlations with efficacy. Conclusions: Atezolizumab was generally well tolerated in patients with mCRPC, with a safety profile consistent with other tumor types. In heavily pretreated patients, atezolizumab monotherapy demonstrated evidence of disease control; however, its limited efficacy suggests a combination approach may be needed.

PD-1 and PD-L1 act to restrict T-cell responses in cancer and contribute to self-tolerance. Consistent with this role, PD-1 checkpoint inhibitors have been associated with immune-related adverse events (irAEs), immune toxicities thought to be autoimmune in origin. Analyses of dermatological irAEs have identified an association with improved overall survival (OS) following anti-PD-(L)1 therapy, but the factors that contribute to this relationship are poorly understood. We collected germline whole genome sequencing data from IMvigor211, a recent phase 3 randomized controlled trial comparing atezolizumab (anti-PD-L1) monotherapy to chemotherapy in bladder cancer. We found that high vitiligo, high psoriasis, and low atopic dermatitis polygenic risk scores (PRSs) were associated with longer OS under anti-PD-L1 monotherapy as compared to chemotherapy, reflecting the Th17 polarization of these diseases. PRSs were not correlated with tumor mutation burden, PD-L1 immunohistochemistry, nor T-effector gene signatures. Shared genetic factors impact risk for dermatological autoimmunity and anti-PD-L1 monotherapy in bladder cancer.

Although elevated plasma interleukin-8 (pIL-8) has been associated with poor outcome to immune checkpoint blockade 1, this has not been comprehensively evaluated in large randomized studies. Here we analyzed circulating pIL-8 and IL8 gene expression in peripheral blood mononuclear cells and tumors of patients treated with atezolizumab (anti-PD-L1 monoclonal antibody) from multiple randomized trials representing 1,445 patients with metastatic urothelial carcinoma (mUC) and metastatic renal cell carcinoma. High levels of IL-8 in plasma, peripheral blood mononuclear cells and tumors were associated with decreased efficacy of atezolizumab in patients with mUC and metastatic renal cell carcinoma, even in tumors that were classically CD8+ T cell inflamed. Low baseline pIL-8 in patients with mUC was associated with increased response to atezolizumab and chemotherapy. Patients with mUC who experienced on-treatment decreases in pIL-8 exhibited improved overall survival when treated with atezolizumab but not with chemotherapy. Single-cell RNA sequencing of the immune compartment showed that IL8 is primarily expressed in circulating and intratumoral myeloid cells and that high IL8 expression is associated with downregulation of the antigen-presentation machinery. Therapies that can reverse the impacts of IL-8-mediated myeloid inflammation will be essential for improving outcomes of patients treated with immune checkpoint inhibitors.

BackgroundCD8+ tissue-resident memory T (TRM) cells, marked by CD103 (ITGAE) expression, are thought to actively suppress cancer progression, leading to the hypothesis that their presence in tumors may predict response to immunotherapy.MethodsHere, we test this by combining high-dimensional single-cell modalities with bulk tumor transcriptomics from 1868 patients enrolled in lung and bladder cancer clinical trials of atezolizumab (anti-programmed cell death ligand 1 (PD-L1)).ResultsITGAE was identified as the most significantly upregulated gene in inflamed tumors. Tumor CD103+ CD8+ TRM cells exhibited a complex phenotype defined by the expression of checkpoint regulators, cytotoxic proteins, and increased clonal expansion.ConclusionsOur analyses indeed demonstrate that the presence of CD103+ CD8+ TRM cells, quantified by tracking intratumoral CD103 expression, can predict treatment outcome, suggesting that patients who respond to PD-1/PD-L1 blockade are those who exhibit an ongoing antitumor T-cell response.

Summary Background Despite standard curative-intent treatment with neoadjuvant cisplatin-based chemotherapy, followed by radical surgery in eligible patients, muscle-invasive urothelial carcinoma has a high recurrence rate and no level 1 evidence for adjuvant therapy. We aimed to evaluate atezolizumab as adjuvant therapy in patients with high-risk muscle-invasive urothelial carcinoma. Method In the IMvigor010 study, a multicentre, open-label, randomised, phase 3 trial done in 192 hospitals, academic centres, and community oncology practices across 24 countries or regions, patients aged 18 years and older with histologically confirmed muscle-invasive urothelial carcinoma and an Eastern Cooperative Oncology Group performance status of 0, 1, or 2 were enrolled within 14 weeks after radical cystectomy or nephroureterectomy with lymph node dissection. Patients had ypT2–4a or ypN+ tumours following neoadjuvant chemotherapy or pT3–4a or pN+ tumours if no neoadjuvant chemotherapy was received. Patients not treated with neoadjuvant chemotherapy must have been ineligible for or declined cisplatin-based adjuvant chemotherapy. No post-surgical radiotherapy or previous adjuvant chemotherapy was allowed. Patients were randomly assigned (1:1) using a permuted block (block size of four) method and interactive voice-web response system to receive 1200 mg atezolizumab given intravenously every 3 weeks for 16 cycles or up to 1 year, whichever occurred first, or to observation. Randomisation was stratified by previous neoadjuvant chemotherapy use, number of lymph nodes resected, pathological nodal status, tumour stage, and PD-L1 expression on tumour-infiltrating immune cells. The primary endpoint was disease-free survival in the intention-to-treat population. Safety was assessed in patients who either received at least one dose of atezolizumab or had at least one post-baseline safety assessment. This trial is registered with ClinicalTrials.gov, NCT02450331, and is ongoing but not recruiting patients. Findings Between Oct 5, 2015, and July 30, 2018, we enrolled 809 patients, of whom 406 were assigned to the atezolizumab group and 403 were assigned to the observation group. Median follow-up was 21·9 months (IQR 13·2–29·8). Median disease-free survival was 19·4 months (95% CI 15·9–24·8) with atezolizumab and 16·6 months (11·2–24·8) with observation (stratified hazard ratio 0·89 [95% CI 0·74–1·08]; p=0·24). The most common grade 3 or 4 adverse events were urinary tract infection (31 [8%] of 390 patients in the atezolizumab group vs 20 [5%] of 397 patients in the observation group), pyelonephritis (12 [3%]) vs 14 [4%]), and anaemia (eight [2%] vs seven [2%]). Serious adverse events occurred in 122 (31%) patients who received atezolizumab and 71 (18%) who underwent observation. 63 (16%) patients who received atezolizumab had a treatment-related grade 3 or 4 adverse event. One treatment-related death, due to acute respiratory distress syndrome, occurred in the atezolizumab group. Interpretation To our knowledge, IMvigor010 is the largest, first-completed phase 3 adjuvant study to evaluate the role of a checkpoint inhibitor in muscle-invasive urothelial carcinoma. The trial did not meet its primary endpoint of improved disease-free survival in the atezolizumab group over observation. Atezolizumab was generally tolerable, with no new safety signals; however, higher frequencies of adverse events leading to discontinuation were reported than in metastatic urothelial carcinoma studies. These data do not support the use of adjuvant checkpoint inhibitor therapy in the setting evaluated in IMvigor010 at this time. Funding F Hoffmann-La Roche/Genentech.

Supplemental Digital Content is available in the text., Cancer immunotherapies, such as atezolizumab, are proving to be a valuable therapeutic strategy across indications, including non–small cell lung cancer (NSCLC) and urothelial cancer (UC). Here, we describe a diagnostic assay that measures programmed-death ligand 1 (PD-L1) expression, via immunohistochemistry, to identify patients who will derive the most benefit from treatment with atezolizumab, a humanized monoclonal anti-PD-L1 antibody. We describe the performance of the VENTANA PD-L1 (SP142) Assay in terms of specificity, sensitivity, and the ability to stain both tumor cells (TC) and tumor-infiltrating immune cells (IC), in NSCLC and UC tissues. The reader precision, repeatability and intermediate precision, interlaboratory reproducibility, and the effectiveness of pathologist training on the assessment of PD-L1 staining on both TC and IC were evaluated. We detail the analytical validation of the VENTANA PD-L1 (SP142) Assay for PD-L1 expression in NSCLC and UC tissues and show that the assay reliably evaluated staining on both TC and IC across multiple expression levels/clinical cut-offs. The reader precision showed high overall agreement when compared with consensus scores. In addition, pathologists met the predefined training criteria (≥85.0% overall percent agreement) for the assessment of PD-L1 expression in NSCLC and UC tissues with an average overall percent agreement ≥95.0%. The assay evaluates PD-L1 staining on both cell types and is robust and precise. In addition, it can help to identify those patients who may benefit the most from treatment with atezolizumab, although treatment benefit has been demonstrated in an all-comer NSCLC and UC patient population.

Summary Background Few options exist for patients with locally advanced or metastatic urothelial carcinoma after progression with platinum-based chemotherapy. We aimed to assess the safety and efficacy of atezolizumab (anti-programmed death-ligand 1 [PD-L1]) versus chemotherapy in this patient population. Methods We conducted this multicentre, open-label, phase 3 randomised controlled trial (IMvigor211) at 217 academic medical centres and community oncology practices mainly in Europe, North America, and the Asia-Pacific region. Patients (aged ≥18 years) with metastatic urothelial carcinoma who had progressed after platinum-based chemotherapy were randomly assigned (1:1), via an interactive voice and web response system with a permuted block design (block size of four), to receive atezolizumab 1200 mg or chemotherapy (physician's choice: vinflunine 320 mg/m 2 , paclitaxel 175 mg/m 2 , or 75 mg/m 2 docetaxel) intravenously every 3 weeks. Randomisation was stratified by PD-L1 expression (expression on vs ≥5% of tumour-infiltrating immune cells [IC2/3]), chemotherapy type (vinflunine vs taxanes), liver metastases (yes vs no), and number of prognostic factors (none vs one, two, or three). Patients and investigators were aware of group allocation. Patients, investigators, and the sponsor were masked to PD-L1 expression status. The primary endpoint of overall survival was tested hierarchically in prespecified populations: IC2/3, followed by IC1/2/3, followed by the intention-to-treat population. This study, which is ongoing but not recruiting participants, is registered with ClinicalTrials.gov, number NCT02302807. Findings Between Jan 13, 2015, and Feb 15, 2016, we randomly assigned 931 patients from 198 sites to receive atezolizumab (n=467) or chemotherapy (n=464). In the IC2/3 population (n=234), overall survival did not differ significantly between patients in the atezolizumab group and those in the chemotherapy group (median 11·1 months [95% CI 8·6–15·5; n=116] vs 10·6 months [8·4–12·2; n=118]; stratified hazard ratio [HR] 0·87, 95% CI 0·63–1·21; p=0·41), thus precluding further formal statistical analysis. Confirmed objective response rates were similar between treatment groups in the IC2/3 population: 26 (23%) of 113 evaluable patients had an objective response in the atezolizumab group compared with 25 (22%) of 116 patients in the chemotherapy group. Duration of response was numerically longer in the atezolizumab group than in the chemotherapy group (median 15·9 months [95% CI 10·4 to not estimable] vs 8·3 months [5·6–13·2]; HR 0·57, 95% CI 0·26–1·26). In the intention-to-treat population, patients receiving atezolizumab had fewer grade 3–4 treatment-related adverse events than did those receiving chemotherapy (91 [20%] of 459 vs 189 [43%] of 443 patients), and fewer adverse events leading to treatment discontinuation (34 [7%] vs 78 [18%] patients). Interpretation Atezolizumab was not associated with significantly longer overall survival than chemotherapy in patients with platinum-refractory metastatic urothelial carcinoma overexpressing PD-L1 (IC2/3). However, the safety profile for atezolizumab was favourable compared with chemotherapy, Exploratory analysis of the intention-to-treat population showed well-tolerated, durable responses in line with previous phase 2 data for atezolizumab in this setting. Funding F Hoffmann-La Roche, Genentech.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Summary Background Atezolizumab can induce sustained responses in metastatic urothelial carcinoma. We report the results of IMvigor130, a phase 3 trial that compared atezolizumab with or without platinum-based chemotherapy versus placebo plus platinum-based chemotherapy in first-line metastatic urothelial carcinoma. Methods In this multicentre, phase 3, randomised trial, untreated patients aged 18 years or older with locally advanced or metastatic urothelial carcinoma, from 221 sites in 35 countries, were randomly assigned to receive atezolizumab plus platinum-based chemotherapy (group A), atezolizumab monotherapy (group B), or placebo plus platinum-based chemotherapy (group C). Patients received 21-day cycles of gemcitabine (1000 mg/m2 body surface area, administered intravenously on days 1 and 8 of each cycle), plus either carboplatin (area under the curve of 4·5 mg/mL per min administered intravenously) or cisplatin (70 mg/m2 body surface area administered intravenously) on day 1 of each cycle with either atezolizumab (1200 mg administered intravenously on day 1 of each cycle) or placebo. Group B patients received 1200 mg atezolizumab, administered intravenously on day 1 of each 21-day cycle. The co-primary efficacy endpoints for the intention-to-treat population were investigator-assessed Response Evaluation Criteria in Solid Tumours 1.1 progression-free survival and overall survival (group A vs group C) and overall survival (group B vs group C), which was to be formally tested only if overall survival was positive for group A versus group C. The trial is registered with ClinicalTrials.gov , NCT02807636 . Findings Between July 15, 2016, and July 20, 2018, we enrolled 1213 patients. 451 (37%) were randomly assigned to group A, 362 (30%) to group B, and 400 (33%) to group C. Median follow-up for survival was 11·8 months (IQR 6·1–17·2) for all patients. At the time of final progression-free survival analysis and interim overall survival analysis (May 31, 2019), median progression-free survival in the intention-to-treat population was 8·2 months (95% CI 6·5–8·3) in group A and 6·3 months (6·2–7·0) in group C (stratified hazard ratio [HR] 0·82, 95% CI 0·70–0·96; one-sided p=0·007). Median overall survival was 16·0 months (13·9–18·9) in group A and 13·4 months (12·0–15·2) in group C (0·83, 0·69–1·00; one-sided p=0·027). Median overall survival was 15·7 months (13·1–17·8) for group B and 13·1 months (11·7–15·1) for group C (1·02, 0·83–1·24). Adverse events that led to withdrawal of any agent occurred in 156 (34%) patients in group A, 22 (6%) patients in group B, and 132 (34%) patients in group C. 50 (11%) patients in group A, 21 (6%) patients in group B, and 27 (7%) patients in group C had adverse events that led to discontinuation of atezolizumab or placebo. Interpretation Addition of atezolizumab to platinum-based chemotherapy as first-line treatment prolonged progression-free survival in patients with metastatic urothelial carcinoma. The safety profile of the combination was consistent with that observed with the individual agents. These results support the use of atezolizumab plus platinum-based chemotherapy as a potential first-line treatment option for metastatic urothelial carcinoma. Funding F Hoffmann-La Roche and Genentech.

Antibodies targeting PD-1 or its ligand 1 PD-L1 such as atezolizumab, have great efficacy in a proportion of metastatic urothelial cancers1,2. Biomarkers may facilitate identification of these responding tumors3. Neoadjuvant use of these agents is associated with pathological complete response in a spectrum of tumors, including urothelial cancer4-7. Sequential tissue sampling from these studies allowed for detailed on-treatment biomarker analysis. Here, we present a single-arm phase 2 study, investigating two cycles of atezolizumab before cystectomy in 95 patients with muscle-invasive urothelial cancer (ClinicalTrials. gov identifier: NCT02662309). Pathological complete response was the primary endpoint. Secondary endpoints focused on safety, relapse-free survival and biomarker analysis. The pathological complete response rate was 31% (95% confidence interval: 21-41%), achieving the primary efficacy endpoint. Baseline biomarkers showed that the presence of preexisting activated T cells was more prominent than expected and correlated with outcome. Other established biomarkers, such as tumor mutational burden, did not predict outcome, differentiating this from the metastatic setting. Dynamic changes to gene expression signatures and protein biomarkers occurred with therapy, whereas changes in DNA alterations with treatment were uncommon. Responding tumors showed predominant expression of genes related to tissue repair after treatment, making tumor biomarker interpretation challenging in this group. Stromal factors such as transforming growth factor-beta and fibroblast activation protein were linked to resistance, as was high expression of cell cycle gene signatures after treatment.

Background: The IMvigor130 primary analysis demonstrated a statistically significant progression-free survival (PFS) benefit and encouraging OS with atezo + plt/gem (Arm A) vs placebo + plt/gem (Arm C) as first-line mUC treatment, although interim OS results did not cross the pre-specified threshold for significance (Galsky Lancet 2020). Here we report the 2nd interim OS for Arm A vs C, including efficacy by type of chemotherapy (chemo) given. Methods: Pts were randomized 1:1:1 to Arm A, B (atezo monotherapy) or C. Investigators pre-specified the type of chemo pts would receive if assigned to Arms A or C (gem + either cisplatin or carboplatin). Co-primary endpoints (EPs) were RECIST 1.1 PFS and OS (Arm A vs C; ITT) and OS (Arm B vs C; ITT, IC2/3) tested using a hierarchical approach. Safety and secondary efficacy EPs (objective response rate and duration of response) are reported. Exploratory OS analyses by type of chemo were pre-specified. Results: As of data cutoff, June 14, 2020 (median follow-up, 13.3 mo), OS event rates were 67% in Arm A and 70% in Arm C. Efficacy data are shown (Table). Subsequent non-protocol immunotherapy use was 7% in Arm A vs 24% in Arm C. Of pts in the safety population (Arm A: 454; Arm C: 389), 81% and 80%, respectively, had a Gr 3/4 treatment-related AE (TRAE). No new Gr 5 TRAEs occurred since the 1st analysis (Gr 5 TRAEs: 2% in Arm A vs 1% in Arm C). Gr 3/4 AEs of special interest occurred in 9% in Arm A and 4% in Arm C. Conclusions: OS with atezo + plt/gem vs placebo + plt/gem in this updated analysis of IMvigor130 was consistent with the 1st interim analysis (not yet statistically significant). The impact of atezo plus chemo on outcomes may differ based on the specific platinum regimen; these exploratory findings warrant further investigation. OS follow-up is ongoing. Safety profile of atezo + plt/gem was consistent with each agent. IMvigor130 efficacy (second interim OS analysis)Arm A:Arm C:atezo + plt/gemplacebo + plt/gem(n=451)(n=400)OS HR (95% CI)aITT0.84 (0.71, 1.00); P=0.026bCisplatin (n=273)0.73 (0.54, 0.98)PD-L1 IC2/3 (n=69)c0.66 (0.32, 1.36)PD-L1 IC0/1 (n=204)c0.72 (0.52, 1.01)Carboplatin (n=578)0.91 (0.74, 1.10)PD-L1 IC2/3 (n=130)c0.80 (0.52, 1.23)PD-L1 IC0/1 (n=448)c0.94 (0.75, 1.18)Median OS (95% CI), moITT16.1 (14.2, 18.8)13.4 (11.9, 15.2)Cisplatin21.6 (17.5, 25.4)14.6 (11.7, 18.4)Carboplatin14.3 (12.0, 16.5)13.0 (10.6, 15.2)Objective response rate (95% CI), %ITT (n=844)d48 (43, 53)45 (40, 50)Cisplatin (n=271)d49 (40, 57)50 (41, 58)Carboplatin (n=573)d48 (42, 53)42 (36, 48)Complete response rate (95% CI), %ITT (n=844)d13 (10, 17)7 (5, 10)Cisplatin (n=271)d17 (11, 24)9 (5, 15)Carboplatin (n=573)d12 (9, 16)6 (4, 10)Median duration of response (95% CI), moeAll responders (n=391)9.3 (8.0, 10.7)8.2 (6.3, 8.5)Cisplatin (n=133)13.2 (10.4, 22.5)8.3 (6.3, 13.3)Carboplatin (n=258)8.1 (6.5, 10.2)7.1 (6.2, 8.5)IC, tumor-infiltrating immune cells; ITT, intention to treat.aHR for the ITT population is stratified by PD-L1 IC status (IC0 vs IC1 vs IC2/3), Bajorin risk factor score (0, 1, 2 and/or liver metastases), investigator's choice of cisplatin/gemcitabine vs carboplatin/gemcitabine and enrollment stage. HRs for subgroups are stratified by enrollment stage.bOne-sided; not statistically significant (O'Brien-Fleming stopping boundary P value 0.014).cPD-L1-expressing IC covering ≥5% (IC2/3) or Citation Format: Matthew D. Galsky, José Ángel Arranz, Enrique Grande, Maria De Santis, Ian D. Davis, Eiji Kikuchi, Xavier Garcia del Muro, Se Hoon Park, Ugo De Giorgi, Boris Alekseev, Marina Mencinger, Kouji Izumi, Javier Puente, Jian-Ri Li, Peter H. O'Donnell, Xiaodong Shen, Chooi Lee, Almut Mecke, Sanjeev Mariathasan, Aristotelis Bamias. Atezolizumab (atezo) + platinum/gemcitabine (plt/gem) vs placebo + plt/gem in patients (pts) with previously untreated locally advanced or metastatic urothelial carcinoma (mUC): Updated overall survival (OS) from the randomized phase III study IMvigor130 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT042.

Background: In the IMvigor130 primary analysis in patients (pts) with untreated locally advanced or mUC, a trend toward favorable OS with atezo (anti-PD-L1) monotherapy (Arm B) vs placebo + platinum/gemcitabine (plt/gem; Arm C) was seen in pts with PD-L1-expressing immune cells on ≥5% of the tumor area (IC2/3 per VENTANA SP142 IHC assay; Galsky Lancet 2020). We report clinical outcomes in Arm B vs C from the second interim OS analysis, including efficacy in cisplatin-ineligible pts. Methods: Pts were randomized 1:1:1 to Arm A (atezo + plt/gem [not reported here]), B or C. Co-primary endpoint OS was analyzed via hierarchical statistical testing. Since OS in Arm A vs C was not statistically significant, no formal comparison of Arm B vs C was performed in intention-to-treat (ITT) and IC2/3 pts. Objective response rate (ORR) and duration of response (DOR), both per RECIST 1.1 (secondary endpoints), and safety are reported; additional exploratory subgroup analyses of OS by PD-L1 status in ITT and cisplatin-ineligible pts were also done. Results: Efficacy from the updated OS analysis (June 14, 2020 cutoff; median follow-up, 13.3 mo) is shown in the Table. Exploratory subgroup analyses suggested that OS for IC2/3 pts may be higher in Arm B vs C. In ITT pts, ORR was higher in Arm C, but median DOR was longer in Arm B. In the safety population, Grade (Gr) 3/4 treatment-related adverse events (TRAEs) occurred in 16% and 80% of Arm B and C pts, respectively, and Gr 5 TRAEs in 1% of both arms. Gr 3/4 AEs of special interest (AESIs) occurred in 10% and 4%, respectively, and Gr 5 AESIs in Conclusions: These exploratory efficacy data from an updated OS analysis of IMvigor130 support the benefit of atezo monotherapy as first-line treatment for PD-L1 IC2/3 cisplatin-ineligible mUC. Atezo monotherapy showed a better tolerability profile than chemotherapy. With this longer follow-up, no new safety concerns arose. IMvigor130 efficacy (second interim OS analysis)Efficacy analysis populationArm B: atezoArm C: placebo + chemotherapyaITTOS events/pts (%)241/360 (66.9)246/359 (68.5)Median OS (95% CI), mo15.2 (13.1, 17.7)13.1 (11.7, 15.1)OS HR (95% CI)b0.99 (0.83, 1.19)Responders/ptsc84/359157/356ORR (95% CI), %23.4 (19.1, 28.1)44.1% (38.9, 49.4)Median DOR (95% CI), mod29.6 (15.9, NE)8.1 (6.3, 8.5)PD-L1 IC2/3 populationOS events/pts (%)43/88 (48.9)52/85 (61.2)Median OS (95% CI), mo27.5 (17.7, NE)16.7 (10.0, 26.1)OS HR (95% CI)b0.67 (0.45, 1.02)PD-L1 IC0/1 populationeOS events/pts (%)198/272 (72.8)194/274 (70.8)Median OS (95% CI), mo13.5 (11.1, 16.3)12.8 (11.3, 15.0)OS HR (95% CI)f1.05 (0.86, 1.28)Cisplatin-ineligible pts with PD-L1 IC2/3OS events/pts (%)28/50 (56)30/43 (70)Median OS (95% CI), mo18.6 (14.0, NE)10.0 (7.4, 18.1)OS HR (95% CI)f0.60 (0.36, 1.01)IC, tumor-infiltrating immune cells; NE, not estimable.aConcurrent control arm, which includes pts randomized in Stage 2 when Arm B was added to the study design.bStratified per randomization stratification factors: PD-L1 status (ITT only), Bajorin risk factor score/liver metastases, investigator's choice of platinum (cisplatin or carboplatin) before randomization.cPatients with measurable disease at baseline.dIn pts who had a confirmed response.eIC0/1 = PD-L1 IC Citation Format: Ian D. Davis, Matthew D. Galsky, Xavier Garcia del Muro, Se Hoon Park, Ugo De Giorgi, Boris Alekseev, Marina Mencinger, Kouji Izumi, Javier Puente, Jian-Ri Li, José Ángel Arranz, Aristotelis Bamias, Enrique Grande, Eiji Kikuchi, Almut Mecke, Sanjeev Mariathasan, Xiaodong Shen, Hannah (Xinhui) Huang, Maria De Santis. Updated overall survival (OS) analysis of atezolizumab (atezo) monotherapy vs chemotherapy in untreated locally advanced or metastatic urothelial carcinoma (mUC) in IMvigor130 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT040.

434 Background: Atezo (anti–PD-L1) monotherapy is approved for cis-ineligible pts who have locally advanced or mUC with PD-L1–expressing immune cells on ≥ 5% of the tumor area (IC2/3 per VENTANA SP142 IHC assay). The IMvigor130 primary analysis demonstrated a significant PFS benefit with atezo + platinum/gemcitabine (plt/gem) (arm A) vs placebo (pbo) + plt/gem (arm C) as 1L treatment for mUC (Galsky Lancet 2020); at that time, interim OS data for arm A vs C were encouraging but immature. OS with atezo monotherapy (arm B) could not be formally tested, but favorable efficacy was seen in IC2/3 pts. In this exploratory analysis, we assess outcomes by PD-L1 status in cis-ineligible pts. Methods: Pts were randomized 1:1:1 to arms A, B or C (Galsky Lancet 2020). Evaluation of OS (co-primary EP) was performed via a hierarchical fixed sequence procedure: arm A vs C ITT pts; then, arm B vs C ITT and IC2/3 pts. No formal testing was performed in this exploratory subgroup analyses; OS and RECIST 1.1 ORR (per investigator [secondary EP]) were descriptively evaluated. Results: Efficacy data suggested OS and ORR benefit in atezo-treated cis-ineligible IC2/3 pts (Table). In the overall safety population, all-grade treatment-related AEs (TRAEs) had occurred in 60% and 96% of arm B and C pts, respectively; grade 3-4 TRAEs occurred in 15% and 81%, respectively. Biomarker data evaluating PD-L1 biology (assessed by SP142) and associated transcriptome analysis in arms B vs C will be presented. Conclusions: This exploratory analysis of IMvigor130 pts with 1L cis–ineligible IC2/3 mUC provides additional evidence for clinical benefit with single-agent atezo, a well-tolerated treatment with a distinct safety profile vs chemo. Analyses with longer OS follow-up are warranted. Clinical trial information: NCT02807636 . Research Sponsor: F. Hoffmann-La Roche Ltd[Table: see text]

Background To explore the clinical utility of circulating tumor DNA (ctDNA) with neoadjuvant atezolizumab and radical cystectomy (RC) in muscle invasive urothelial bladder cancer (MIUC). Methods Forty patients from a phase II of neoadjuvant atezolizumab (2 cycles) and RC study in MIUC were included (NCT02662309). Whole-exome sequencing was performed on tumor and matched normal DNA to identify tumor-specific mutations and design a personalized multiplexed PCR Next Generation Sequencing (NGS) assay (bespoke, SignateraTM) for ctDNA detection in plasma. Samples were taken at baseline, post-atezolizumab but pre-surgery, and 1-6 months post-surgery. Response (pathological complete response (pCR) and major pathological response (mPR)) and recurrence free survival (RFS) were correlated with ctDNA status (Pos/Neg) and level. Responders are pCR and mPR patients, whereas non-responders are SD and relapse patients. Results The pCR rate and 2 years RFS was 21.4% and 73.5%, respectively. ctDNA positivity at baseline, post-neoadjuvant pre-surgery (PreCx), and post-surgery (PostCx) were 25/40 (63%), 14/30 (47%), and 5/36 (14%), respectively. ctDNA status was highly prognostic at all timepoints, where PostCx had an HR of 78.11 (p Conclusion ctDNA dynamics across timepoints correlates with clinical outcomes, including response rates and RFS in patients treated with neoadjuvant atezolizumab in MIUC. Immune biomarkers may be relevant in these responses. ctDNA may help the development of personalized therapy in this setting in the future.

Summary Integrated multi-omics evaluation of 823 tumors from advanced renal cell carcinoma (RCC) patients identifies molecular subsets associated with differential clinical outcomes to angiogenesis blockade alone or with a checkpoint inhibitor. Unsupervised transcriptomic analysis reveals seven molecular subsets with distinct angiogenesis, immune, cell-cycle, metabolism, and stromal programs. While sunitinib and atezolizumab + bevacizumab are effective in subsets with high angiogenesis, atezolizumab + bevacizumab improves clinical benefit in tumors with high T-effector and/or cell-cycle transcription. Somatic mutations in PBRM1 and KDM5C associate with high angiogenesis and AMPK/fatty acid oxidation gene expression, while CDKN2A/B and TP53 alterations associate with increased cell-cycle and anabolic metabolism. Sarcomatoid tumors exhibit lower prevalence of PBRM1 mutations and angiogenesis markers, frequent CDKN2A/B alterations, and increased PD-L1 expression. These findings can be applied to molecularly stratify patients, explain improved outcomes of sarcomatoid tumors to checkpoint blockade versus antiangiogenics alone, and develop personalized therapies in RCC and other indications.

Elevated plasma interleukin-8 (IL-8) is a poor prognostic factor for many cancers. However, the association of IL-8 with clinical outcomes to checkpoint inhibition has not been comprehensively evaluated in randomized studies. Moreover, the source of IL-8 and the underlying biology that influences resistance to immune checkpoint inhibitors remain unknown. Here we analyzed circulating IL-8 protein in plasma, and IL8 gene expression in peripheral blood mononuclear cells (PBMC) and tumors of patients treated with atezolizumab (anti-PD-L1 mAb), from multiple randomized trials in metastatic urothelial carcinoma (mUC) and metastatic renal cell carcinoma (mRCC). High levels of IL-8 in plasma, PBMCs and tumors, were associated with decreased efficacy in mUC and mRCC patients treated with atezolizumab, even in tumors that were classically CD8+ T cell inflamed. mUC patients treated with atezolizumab, but not with chemotherapy, who experienced an on-treatment decrease in plasma IL-8, exhibited improved overall survival. IL-8 is primarily expressed in circulating and intratumoral myeloid cells, and high IL8 expression was associated with the downregulation of the antigen presentation machinery in myeloid cells. A better understanding of IL-8-mediated myeloid inflammation in curtailing responses to checkpoint inhibitors is essential for developing new therapies for patients. Citation Format: Kobe Yuen, Lifen Liu, Congfen Li, Deepali Rishipathak, Patrick Williams, Edward Kadel, Hartmut Koeppen, Shravan Madireddi, Shilpa Keerthivasan, Ying-Jun Chen, Zora Modrusen, Romain Banchereau, Ning Leng, Priti Hegde, Mahrukh Huseni, Sanjeev Mariathasan. Systemic and tumor associated IL-8 correlates with resistance to PD-L1 blockade [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2000.

Background: Current treatments for mCRPC include the androgen receptor antagonist enzalutamide (enza). Enza may enhance IFNγ signaling and sensitize tumor cells to immune-mediated cell killing, making it a candidate for combinations with PD-L1/PD-1 inhibitors. Responses have been observed in patients (pts) with mCRPC receiving a PD-L1/PD-1 inhibitor with or without enza. Therefore, atezolizumab (atezo), a humanized anti-PD-L1 monoclonal antibody that inhibits the interaction between PD-L1 and its receptors, is being examined in combination with enza for pts with mCRPC. Methods: IMbassador250 was a Phase III, randomized clinical trial (NCT03016312) evaluating the safety and efficacy of atezo + enza vs enza alone in pts with mCRPC who had progressed on abiraterone and docetaxel, or were not candidates for a taxane regimen (androgen deprivation therapy was not given). Eligible pts had mCRPC or locally advanced, incurable CRPC, ECOG PS 0/1 and no prior immunotherapy or enza/androgen receptor antagonist treatment. After a safety run-in, pts were randomized 1:1 to receive atezo 1200 mg every 3 weeks + enza 160 mg once daily or enza 160 mg once daily only. Stratification factors were prior taxane treatment, presence of liver metastases, level of circulating LDH and pain. The primary endpoint was OS; secondary endpoints included PSA response rate, radiographic PFS, ORR and safety. Tumor tissue and disease progression will be used to assess the relationship between exploratory biomarkers and treatment response. Results: A total of 759 pts were randomized to atezo + enza (n = 379) or enza alone (n = 380). Baseline demographic and clinical characteristics were generally similar between groups. The primary efficacy endpoint of OS was evaluated (data cutoff for efficacy and safety, June 24, 2019), with no difference observed between groups (stratified HR, 1.12 [95% CI: 0.91, 1.37]; P = 0.28). Median OS was 15.2 months (95% CI: 14.0, 17.0) in the atezo + enza group and 16.6 months (95% CI: 14.7, 18.4) in the enza group. Subgroup analyses were consistent with the primary endpoint. Analyses of secondary and exploratory endpoints are ongoing and will be presented. Adverse events (AEs) were consistent with those seen with the treatment components. Nearly all pts had an AE (atezo + enza, 96.5%; enza alone, 91.8%). Treatment-related AEs (TRAEs) were observed in 77.8% and 51.1% of pts, respectively, with Grade 3-4 TRAEs in 28.3% and 9.6% and Grade 5 TRAEs in 1.9% and 0.3% of pts. Conclusions: The combination of atezo + enza did not show an OS improvement vs enza alone, requiring early termination of the study. The observed safety profiles were consistent with the known safety profiles of each treatment. Analyses of secondary outcomes and exploratory endpoints, biomarker studies and treatment response may provide further insight into these findings. Citation Format: Christopher J. Sweeney, Silke Gillessen, Dana Rathkopf, Nobuaki Matsubara, Charles Drake, Karim Fizazi, Josep M. Piulats, Piotr J. Wysocki, Gary L. Buchschacher Jr, Jennifer Doss, Sanjeev Mariathasan, Edward E. Kadel, Kobe Yuen, Asim Datye, Grozdana Rasuo, Darren Tayama, Patrick Williams, Thomas Powles. IMbassador250: A phase III trial comparing atezolizumab with enzalutamide vs enzalutamide alone in patients with metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT014.

5011 Background: Tumor mutational burden (TMB), PD-L1 expression, T-effector gene expression (GE) and a fibroblast TGF-β–response signature (F-TBRS) are associated with clinical outcomes with atezo mono in mUC (Mariathasan, Nature, 2018). Here we explore the potential predictive role of these biomarkers and APOBEC mutagenesis in IMvigor130. Methods: Pts receiving first-line (1L) mUC treatment (tx) were randomized 1:1:1 to atezo + PBC, atezo mono, or placebo + PBC. Coprimary efficacy endpoints were PFS and OS. Planned exploratory biomarker analyses included PD-L1 expression, TMB (FoundationOne), and T-effector GE (RNA-seq). Results: The 851 biomarker-evaluable pts (BEP) were representative of the 1200 ITT pts. Biomarker results are shown in Table. PD-L1 IC2/3 was associated with significantly longer OS for atezo mono vs placebo + PBC and a combination of PD-L1 IC2/3, and high TMB (> 10 muts/Mb) identified a pt subset (≈ 14% of BEP) with particularly favorable outcomes with atezo mono vs placebo + PBC; similar results for PD-L1 and TMB were not seen with atezo + PBC vs placebo + PBC. APOBEC mutagenesis was associated with improved OS with atezo-containing regimens whereas high F-TBRS was associated with inferior OS with atezo mono. Conclusions: These results reinforce the potential predictive nature of biomarkers associated with response/resistance to atezo and highlight potentially distinct biology driving benefit with atezo and atezo + PBC. These findings suggest a possible biomarker-directed approach to 1L mUC tx that warrants mechanistic interrogation and prospective validation. Clinical trial information: NCT02807636 . [Table: see text]

5000 Background: Radical surgery ± cisplatin-based neoadjuvant chemo (NAC) is the mainstay treatment (tx) for MIUC, with no conclusive level 1 evidence for adjuvant chemo (AC). Here we present the primary analysis from IMvigor010, a global, open-label, multicenter, randomized trial of adjuvant atezo (anti–PD-L1; approved in metastatic UC [mUC] settings) in pts with MIUC at high risk of recurrence following primary resection. Methods: Pts with MIUC (bladder, upper tract [UT]), ECOG PS 0-2 and resected tissue for PD-L1 testing on immune cells (IC; VENTANA SP142 assay) were enrolled ≤ 14 wks after radical cystectomy/nephroureterectomy with lymph node (LN) dissection. Pathologic stage: 1) ypT2-4a or ypN+ if pts had NAC or 2) pT3-4a or pN+ if pts did not have NAC. No postsurgical radiation or AC was allowed; if no NAC was given, pts must have been ineligible for or declined cisplatin-based AC. Pts were randomized 1:1 to atezo 1200 mg IV q3w or obs for 16 cycles or 1 y (stratification factors: no. of LNs resected, pathologic nodal status, pathologic tumor stage, PD-L1 status, prior NAC). Disease-free survival (DFS) was the primary endpoint (EP). Final DFS, first interim overall survival (OS; secondary EP) and safety are reported. Results: The ITT population included 809 pts (median follow-up, 21.9 mo). In the atezo and obs arms, respectively, 48% and 47% had NAC; 7% and 6% had UTUC as primary disease; 48% each had LN+ disease. DFS and OS are in Table. Baseline prognostic/clinical factors did not influence DFS tx benefit; stratified HR was 0.81 (95% CI: 0.63, 1.05) in IC0/1 pts (PD-L1 < 5%; n = 417) and 1.01 (0.75, 1.35) in IC2/3 pts (PD-L1 ≥ 5%; n = 392). 16% of atezo-treated pts had a tx-related G3-4 AE. Skin and gastrointestinal toxicities most commonly led to tx discontinuation. Conclusions: IMvigor010, the first phase 3 adjuvant study of a checkpoint inhibitor in MIUC, did not meet its primary EP of DFS. More tx discontinuation due to AEs was seen vs mUC studies. Safety was generally consistent with previous studies. Clinical trial information: NCT02450331 . [Table: see text]

Summary Background First-line chemotherapy for patients with cisplatin-ineligible locally advanced or metastatic urothelial carcinoma is associated with short response duration, poor survival, and high toxicity. This study assessed atezolizumab (anti-programmed death-ligand 1 [PD-L1]) as treatment for metastatic urothelial cancer in cisplatin-ineligible patients. Methods For this single-arm, multicentre, phase 2 study, in 47 academic medical centres and community oncology practices in seven countries in North America and Europe, we recruited previously untreated patients with locally advanced or metastatic urothelial cancer who were cisplatin ineligible. Patients were given 1200 mg intravenous atezolizumab every 21 days until progression. The primary endpoint was independently confirmed objective response rate per Response Evaluation Criteria in Solid Tumors version 1.1 (central review), assessed in prespecified subgroups based on PD-L1 expression and in all patients. All participants who received one or more doses of atezolizumab were included in the primary and safety analyses. This study was registered with ClinicalTrials.gov, number NCT02108652. Findings Between June 9, 2014, and March 30, 2015, we enrolled 123 patients, of whom 119 received one or more doses of atezolizumab. At 17·2 months' median follow-up, the objective response rate was 23% (95% CI 16 to 31), the complete response rate was 9% (n=11), and 19 of 27 responses were ongoing. Median response duration was not reached. Responses occurred across all PD-L1 and poor prognostic factor subgroups. Median progression-free survival was 2·7 months (2·1 to 4·2). Median overall survival was 15·9 months (10·4 to not estimable). Tumour mutation load was associated with response. Treatment-related adverse events that occurred in 10% or more of patients were fatigue (36 [30%] patients), diarrhoea (14 [12%] patients), and pruritus (13 [11%] patients). One treatment-related death (sepsis) occurred. Nine (8%) patients had an adverse event leading to treatment discontinuation. Immune-mediated events occurred in 14 (12%) patients. Interpretation Atezolizumab showed encouraging durable response rates, survival, and tolerability, supporting its therapeutic use in untreated metastatic urothelial cancer. Funding F Hoffmann-La Roche, Genentech.

Therapeutic antibodies that block the programmed death-1 (PD-1)-programmed death-ligand 1 (PD-L1) pathway can induce robust and durable responses in patients with various cancers, including metastatic urothelial cancer. However, these responses only occur in a subset of patients. Elucidating the determinants of response and resistance is key to improving outcomes and developing new treatment strategies. Here we examined tumours from a large cohort of patients with metastatic urothelial cancer who were treated with an anti-PD-L1 agent (atezolizumab) and identified major determinants of clinical outcome. Response to treatment was associated with CD8+ T-effector cell phenotype and, to an even greater extent, high neoantigen or tumour mutation burden. Lack of response was associated with a signature of transforming growth factor β (TGFβ) signalling in fibroblasts. This occurred particularly in patients with tumours, which showed exclusion of CD8+ T cells from the tumour parenchyma that were instead found in the fibroblast- and collagen-rich peritumoural stroma; a common phenotype among patients with metastatic urothelial cancer. Using a mouse model that recapitulates this immune-excluded phenotype, we found that therapeutic co-administration of TGFβ-blocking and anti-PD-L1 antibodies reduced TGFβ signalling in stromal cells, facilitated T-cell penetration into the centre of tumours, and provoked vigorous anti-tumour immunity and tumour regression. Integration of these three independent biological features provides the best basis for understanding patient outcome in this setting and suggests that TGFβ shapes the tumour microenvironment to restrain anti-tumour immunity by restricting T-cell infiltration.

552 Background: Previously, we reported a 3-factor model including tumor mutation burden (TMB), peripheral blood neutrophil/lymphocyte ratio (NLR) and visceral metastasis status to predict tumor regression (c-statistic=0.90) when using ICIs for mUC regardless of line of therapy. We conducted an external validation of this model to determine its ability to predict response. Methods: We utilized data from a phase II trial, IMvigor210, which evaluated atezolizumab (atezo) for post-platinum pts or as first-line therapy for cisplatin-ineligible pts with mUC. Pts with TMB, NLR, visceral metastasis and RECIST1.1 response status available were evaluable. Tumor genomic analysis was performed using FoundationOne, which sequences 324 cancer-related genes. Multivariable regression studied the association of TMB (−5), low NLR (HR=2.591, p=0.00958) and absence of visceral metastasis status (HR=4.105, p=4.04 x 10−5). The c-index of this 3-factor model to predict ≥PR was 0.77. Presence of all 3 favorable factors (TMBhigh, NLRlow, no visceral metastases) was associated with ≥PR in 15/21 pts (71.4%), while the absence of all 3 factors (TMBlow, NLRhigh, visceral metastases) was associated with ≥PR in 2/37 pts (5.4%). Conclusions: A 3-factor model combining readily available clinical and genomic variables including TMB, NLR and visceral metastasis status was validated to robustly predict RECIST 1.1 response in pts with mUC receiving atezo as first-line or post-platinum therapy. This model may improve the therapeutic index and cost efficacy of atezo.

569 Background: Despite the benefits of PD1/L1 inhibitors in metastatic urothelial carcinoma (mUC), the durable benefits accrue mostly to a minority of patients (pts) who attain ≥partial response (PR) by RECIST 1.1. There is a pressing need to identify pts with a low probability of response, who may be diverted to other regimens or trials. Biomarkers associated with response such as PD-L1 expression, intrinsic subtype and tumor mutational burden (TMB) are suboptimal. We studied the ability of agnostic gene expression analysis for association with response. Methods: A retrospective cohort of FFPE tumor samples that underwent RNAseq utilizing pts from the phase II IMvigor210 trial were analyzed. In this study, pts received atezo, a PD-L1 inhibitor, in either the post-platinum or first line cisplatin-ineligible setting. All reads were collapsed to gene level transcript per million (TPM) values, followed by feature selection based on enrichment observed in patients with PR vs progressive disease (PD) as well as complete response (CR) vs PD. A transcriptional biomarker was then designed based on these gene-level enrichment scores, followed by generation of a synthetic “metagene” reflecting a composite of the top single gene predictors. Results: A total of 298 pts were evaluable from the IMvigor210 dataset. The favorable and unfavorable composite biomarker ‘metagene’ was robustly associated with high or low probability of ≥PR, regardless of line of atezolizumab therapy (Table). Area Under the Curve (AUC) for this biomarker was 0.73. Notably, an indeterminate category of the metagene was associated with ≥PR in an intermediate proportion of pts, consistent with meaningful discrimination of response categories. Conclusions: A metagene based on tumor gene expression robustly identified pts with mUC who exhibited ≥PR with atezo. With validation across other PD1/L1 inhibitors and refinement in combination with clinical factors, the metagene may enable the selection of the most suitable pts with mUC for PD1/L1 inhibitors.[Table: see text]

Background Patients with metastatic urothelial carcinoma have few treatment options after failure of platinum-based chemotherapy. In this trial, we assessed treatment with atezolizumab, an engineered humanised immunoglobulin G1 monoclonal antibody that binds selectively to programmed death ligand 1 (PD-L1), in this patient population. Methods For this multicentre, single-arm, two-cohort, phase 2 trial, patients (aged >= 18 years) with inoperable locally advanced or metastatic urothelial carcinoma whose disease had progressed after previous platinum-based chemotherapy were enrolled from 70 major academic medical centres and community oncology practices in Europe and North America. Key inclusion criteria for enrolment were Eastern Cooperative Oncology Group performance status of 0 or 1, measurable disease defined by Response Evaluation Criteria In Solid Tumors version 1.1 (RECIST v1.1), adequate haematological and end-organ function, and no autoimmune disease or active infections. Formalin-fixed paraffin-embedded tumour specimens with sufficient viable tumour content were needed from all patients before enrolment. Patients received treatment with intravenous atezolizumab (1200 mg, given every 3 weeks). PD-L1 expression on tumour-infiltrating immune cells (ICs) was assessed prospectively by immunohistochemistry. The co-primary endpoints were the independent review facility-assessed objective response rate according to RECIST v1.1 and the investigator-assessed objective response rate according to immune-modified RECIST, analysed by intention to treat. A hierarchical testing procedure was used to assess whether the objective response rate was significantly higher than the historical control rate of 10% at an a level of 0.05. This study is registered with ClinicalTrials.gov, number NCT02108652. Findings Between May 13, 2014, and Nov 19, 2014, 486 patients were screened and 315 patients were enrolled into the study. Of these patients, 310 received atezolizumab treatment (five enrolled patients later did not meet eligibility criteria and were not dosed with study drug). The PD-L1 expression status on infiltrating immune cells (ICs) in the tumour microenvironment was defined by the percentage of PD-L1-positive immune cells: IC0 (= 1% but < 5%), and IC2/3 (>= 5%). The primary analysis (data cutoff May 5, 2015) showed that compared with a historical control overall response rate of 10%, treatment with atezolizumab resulted in a significantly improved RECIST v1.1 objective response rate for each prespecified immune cell group (IC2/3: 27% [95% CI 19-37], p< 0.0001; IC1/2/3: 18% [13-24], p= 0.0004) and in all patients (15% [11-20], p= 0.0058). With longer follow-up (data cutoff Sept 14, 2015), by independent review, objective response rates were 26% (95% CI 18-36) in the IC2/3 group, 18% (13-24) in the IC1/2/3 group, and 15% (11-19) overall in all 310 patients. With a median follow-up of 11.7 months (95% CI 11.4-12.2), ongoing responses were recorded in 38 (84%) of 45 responders. Exploratory analyses showed The Cancer Genome Atlas (TCGA) subtypes and mutation load to be independently predictive for response to atezolizumab. Grade 3-4 treatment-related adverse events, of which fatigue was the most common (five patients [2%]), occurred in 50 (16%) of 310 treated patients. Grade 3-4 immune-mediated adverse events occurred in 15 (5%) of 310 treated patients, with pneumonitis, increased aspartate aminotransferase, increased alanine aminotransferase, rash, and dyspnoea being the most common. No treatment-related deaths occurred during the study. Interpretation Atezolizumab showed durable activity and good tolerability in this patient population. Increased levels of PD-L1 expression on immune cells were associated with increased response. This report is the first to show the association of TCGA subtypes with response to immune checkpoint inhibition and to show the importance of mutation load as a biomarker of response to this class of agents in advanced urothelial carcinoma.

Introduction Immune checkpoint blockade such as inhibition of programmed death-1 (PD-1) or programmed death-ligand 1 (PD-L1) has been shown to be effective in metastatic urothelial cancer (mUC) and many other types of cancers. Despite its robust efficacy, a large proportion of patients still fail to show durable responses; therefore, it is important to understand the mechanisms that drive clinical responses, as well as the pathways associated with lack of response. Circulating peripheral biomarkers are particularly useful as readily accessible and minimally invasive markers to enable monitoring both tumor growth and responses to treatment. Methods Baseline plasma from 337 patients treated with an anti-PD-L1 (atezolizumab) in the mUC Ph2 trial IMvigor210 (NCT02108652) were analyzed using a Myriad-RBM panel. To further characterize the findings, single-cell RNA sequencing (scRNAseq) was performed with PBMC isolated from responders and non-responders (n=5 each) to atezolizumab in the same trial. NanoString gene expression levels of the PBMC isolated from mUC patients in IMvigor210 was used to validate the identified signatures. Results High levels of CXCL9 (HR: 0.692, CI: 0.529-0.903, p=0.006) and leptin (HR: 0.633, CI: 0.485-0.825, p=0.001) were associated with better overall survival (OS), whereas high levels of pro-inflammatory cytokines IL6 (HR: 2.744, CI: 2.084-3.612, p Conclusion Peripheral biomarker analysis revealed that adaptive immune signatures to be associated better clinical outcome, whereas innate inflammation and angiogenesis signatures to be correlated with worse clinical outcome to anti-PD-L1 immunotherapy. The link between IL6 and angiogenesis in the tumor microenvironment will be further characterized. Understanding the genes and pathways associated with outcomes will shed light on peripheral biomarker development. Citation Format: Kobe C. Yuen, Vinita Gupta, Congfen Li, Deepali Rishipathak, Edward E. Kadel, Ying-Jiun J. Chen, Leonard D. Goldstein, Zora Modrusan, Sanjeev Mariathasan. Associations of peripheral biomarkers to outcomes to anti-PD-L1 immune checkpoint blockade in metastatic urothelial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2676.

Robert Dreicer*, Charlottesville, VA; Michiel S. van der Heijden, Amsterdam, Netherlands; Petros Grivas, Cleveland, OH; Jean Hoffman-Censits, Philadelphia, PA; Yohann Loriot, Villejuif, France; Margitta Retz, Munich, Germany; Nicholas J Vogelzang, Las Vegas, NV; Jose Luis Perez-Gracia, Pamplona, Spain; Arash Rezazadeh Kalebasty, Louisville, KY; Sergio Bracarda, Arezzo, Italy; Evan Y Yu, Seattle, WA; Christopher Hoimes, Cleveland, OH; Joaquim Bellmunt, Boston, MA; David I Quinn, Los Angeles, CA; Daniel P. Petrylak, New Haven, CT; Syed A Hussain, Liverpool, United Kingdom; Na Cui, Sanjeev Mariathasan, Fatema Legrand, South San Francisco, CA; Jonathan E. Rosenberg, New York, NY

Checkpoint inhibitor blockade can result in robust and durable anti-tumor responses in various cancers, including metastatic urothelial cancer (mUC). However, these responses only occur in a subset of patients. Identifying determinants of response and resistance to cancer immunotherapy is critical for extending therapeutic benefit to more patients. Atezolizumab (anti-PD-L1) was approved in the US for the treatment of mUC based on the single-arm Phase II study IMvigor210 (NCT02108652; n= 429 patients). Here, we examined the biology underlying primary immune escape and responsiveness to anti-PD-L1 in tumor samples of patients from IMvigor210. Methods: PD-L1 expression on tumor-infiltrating immune cells was assessed with SP142 IHC. Exploratory analyses in evaluable pre-treatment tissues included: (i) CD8 IHC analysis to define immune deserts, excluded and inflamed subtypes (ii) whole-transcriptome RNA sequencing to identify pathways associated with response and to perform tumor molecular subtyping, (iii) targeted mutational profiling (FoundationOne) to estimate tumor mutation burden, and (iv) whole-exome sequencing to predict putative neoantigens. EMT6-grafted BALB/c mice treated with anti-TGF-β and/or anti-PD-L1 antibodies were evaluated for tumor growth inhibition. Results: Response was associated with CD8+ T-effector gene expression and, to an even greater extent, high neoantigen or tumor mutation burden (TMB). Gene expression pathways significantly associated with high TMB were those involved in cell cycle, DNA replication, DNA damage response (DDR). Tumors with mutations in DDR gene sets also had significantly high TMB and response rates. Lack of response was associated with a signature of transforming growth factor β (TGF-β) signaling in fibroblasts, particularly in patients with CD8+ T cells that were excluded from the tumor parenchyma and instead found in the fibroblast- and collagen-rich peritumoral stroma. Using a mouse model that recapitulates this immune excluded phenotype, we found that therapeutic administration of a TGF-β blocking antibody together with anti-PD-L1 reduced TGF-β signaling in stromal cells, facilitated T cell penetration into the centre of the tumor, and provoked vigorous anti-tumor immunity and tumor regression. Conclusion: Pre-existing T-cell immunity and TMB are associated with response to atezolizumab in mUC, whereas TGF-β signaling in the stroma is a negative indicator of response, especially in immune-excluded tumors, a common phenotype of mUC. Integration of these three independent biological features provides a best basis for understanding clinical outcomes in this setting. Furthermore, the data suggests that TGF-β shapes the tumor microenvironment to restrain anti-tumor activity by restricting T cell infiltration. Citation Format: Sanjeev Mariathasan, Shannon J. Turley, Dorothee Nickles, Alessandra Castiglioni, Kobe Yuen, Yulei Wang, Edward E. Kadel, Hartmut Koeppen, Jillian L. Astarita, Rafael Cubas, Suchit Jhunjhunwala, Yagai Yang, Yasin Şenbabaoğlu, Ira Mellman, Daniel S. Chen, Priti Hegde, Richard Bourgon, Thomas Powles. A balance of genomic instability, tumor-immune contexture and TGF-β signaling contributing to exclusion of T cells governs response to PD-L1 checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2979.

12000Background: PD-L1 expression has limitations as a biomarker for checkpoint immunotherapy (CI). Prior atezolizumab (atezo) monotherapy studies suggest improved efficacy in high tissue tumor mut...

409 Background: IMvigor211 is a global study of atezo vs chemo in platinum-treated mUC. The study did not meet its primary endpoint of overall survival (OS) in programmed death-ligand 1 (PD-L1)–selected patients (pts),1 but exploratory analyses showed improved OS for atezo in the intent-to-treat (ITT) population. Here we compare clinical outcomes in ITT and prespecified PD-L1 subgroups with those in subgroups defined by immune transcriptional gene expression (tGE) signatures and TMB. Methods: Pts with ≤ 2 prior lines of therapy for mUC who progressed during or following platinum treatment were randomized 1:1 to atezo or chemo (vinflunine, paclitaxel or docetaxel, per physician). The primary endpoint was OS, hierarchically compared between treatment arms in PD-L1–selected and ITT pts. Planned exploratory biomarker analyses included tGE (RNA-seq) and TMB (FoundationOne). Results: The ITT population included 931 pts (atezo arm, 467; chemo arm, 464), and biomarker-evaluable subgroups were representative of the ITT population. PD-L1 expression positively correlated with tGE (R = 0.61) but not TMB (R = 0.13). OS and hazard ratios (HRs) are listed in the Table. Conclusions: In this randomized Phase III study, we show that high PD-L1 and high tGE are associated with improved outcomes with both chemo and atezo. In contrast, higher TMB predicted OS in favor of atezo; however, clinical benefit with atezo was also seen in the ITT population. Clinical trial information: NCT02302807. [Table: see text]

187 Background: In the past decade, several therapies have been approved for mCRPC. However, most pts develop resistance and experience disease progression. Thus, there remains a high unmet need. Atezo (anti–PD-L1) blocks the interaction between PD-L1 and its receptors, PD-1 and B7.1, thereby restoring anti-tumor immunity. Atezo has demonstrated clinical efficacy in many tumor types. Here we report the clinical safety and activity of atezo in pts with mCRPC from a Phase Ia study (PCD4989g; NCT01375842). Methods: Eligible pts previously received enzalutamide and/or sipuleucel-T for mCRPC. Pts also had PSA or radiographic progression prior to enrollment. Atezo 1200mg was administered IV q3w. CT and bone scans were performed q6w for 24w and q12w thereafter (q6w if treatment beyond disease progression). Primary objectives were safety and tolerability; OS was an exploratory objective. mCRPC cohort–specific objectives included PSA response, radiographic progression per PCWG2 criteria, soft tissue response per RECIST v1.1 and immune-related response criteria (irRC). Survival follow-up data was collected ≈ every 3 mo until death or loss to follow-up. Results: The 15 pts in the initial mCRPC cohort were evaluated (clinical cutoff: December 31, 2016). 13 pts (87%) had received ≥ 2 prior lines of therapy for mCRPC. Median survival follow-up was 15.8 mo (range, 2.3-23.0). 9 pts (60%) had a treatment-related AE (TRAE); only 1 pt (7%) experienced a Gr 3 TRAE (hyponatremia). No Gr 4-5 TRAEs were reported. The landmark 12-mo OS rate was 55.6% (95% CI: 27.4, 83.7); median OS was not reached (range, 2.3-23.0 mo). Median PFS was 3.4 mo (95% CI: 2.3, 5.7); the 6-mo PFS rate was 26.7% (95% CI: 4.3, 49.1). 1 pt (9%) had a PR per irRC (irPR); 5 pts (45%) had SD per RECIST v1.1 and irRC. 2 pts (13%) had a ≥ 50% decrease in PSA from baseline. The pt who experienced an irPR had increased CD8 expression and expansion of T-cell clones on study treatment. Conclusions: Atezo was well tolerated and demonstrated long-term disease control in pts with heavily pretreated mCRPC, with a 12-mo OS rate of 55.6%. Preliminary biomarker analyses from the pt who experienced an irPR were suggestive of an activated immune response. Clinical trial information: NCT01375842.

11506Background: Atezolizumab (atezo, MPDL3280A) is a humanized IgG1 mAb that prevents the interaction of the ligand PD-L1 with PD-1 and B7.1 and can reinvigorate anticancer T-cell responses. Atezo...

LBA4500 Background: Cisplatin-based chemo is a standard 1L treatment (tx) for mUC and the only tx that prolongs OS; however, age or comorbidities render many pts ineligible, and 30-50% receive no tx. Atezo (MPDL3280A) is active and well tolerated in platinum-treated mUC, justifying testing atezo as 1L tx in cisplatin-ineligible pts. Methods: Pts were chemo naive in the metastatic setting and cisplatin ineligible (renal [GFR > 30 but < 60 mL/min]/hearing impairment, ≥ G2 peripheral neuropathy [PN] or ≥ ECOG PS2). Atezo 1200 mg was given IV q3w until PD (RECIST v1.1). Centrally assessed PD-L1 on tumor infiltrating immune cells (IC; SP142 IHC assay) was scored IC2/3, 1 or 0. The primary efficacy endpoint was confirmed ORR assessed per RECIST v1.1 (central independent review facility) using a data cutoff of Sep 14, 2015. Results: 119 efficacy/safety-evaluable pts of any PD-L1 IC had a median age of 73 y: 21% ≥ 80 y. 18% had prior systemic tx (21% [neo]adjuvant); 10% had radiotherapy. 66% had visceral mets. 71% had CrCl < 60 mL/min; 13% had hearing loss ≥ 25 dB; 6% had prior PN ≥ G2; 20% had ECOG PS2. ORR was 19% (95% CI 13-28; 5% CR), and responses occurred in all IC subgroups (Table; includes DCR/PFS/OS) and in pts with poor prognostic factors. 22/23 responses were ongoing with mDOR not reached. Median follow-up was 8.5 mo (range 0.2-14.3); median tx duration was 15 wk. Atezo was generally well tolerated. Tx-related all-G and G3-4 AEs were seen in 64% and 12% of pts, respectively. Related all-G AEs ≥ 10% included fatigue, pruritus, diarrhea. 1 G5 related AE occurred (sepsis). 3% had a G3-4 immune-mediated AE. Conclusions: Atezo has clinically meaningful activity in 1L cisplatin-ineligible mUC pts, and preliminary OS is encouraging. The durable nature of response and favorable AE profile makes this an attractive alternative to chemo. NCT02108652. Clinical trial information: NCT02108652. [Table: see text]

104Background: Biomarkers of clinical benefit of immunotherapies, such as non-synonymous mutations, mutational load, PD-L1 IHC and immune signatures, have not been systematically evaluated in mUC patients (pts) treated with anti–PD-L1 agents. Methods: Exploratory analyses of immune and genetic predictors of response to atezo were performed on archival tumor specimens from mUC pts (NCT02108652 cohort 2). PD-L1 expression in tumor samples was assessed by IHC (SP142 assay) and associated with response as determined by RECIST v1.1 (central review). Gene expression was quantified by RNA-seq (Illumina TruSeq RNA Access; n = 195); molecular subtypes were assigned as per TCGA. Mutations were detected by genomic profiling (FoundationOne 315-cancer gene panel; n = 150) to estimate overall load. Results: PD-L1 tumor-infiltrating immune cell (IC) status was associated with CD8+ T effector (Teff) gene expression levels (P < 0.0001). Notably, response to atezo was associated with high expression of CXCL9 (P = 0.0057) a...

355 Background: The ORR and survival of mUC patients (pts) who progress after platinum-based chemotherapy (pctx) are poor. Atezolizumab (atezo) reinvigorates antitumor immunity by targeting PD-L1 and has shown promising Ph 1 activity in mUC. Methods: IMvigor 210 cohort 2 (NCT02108652) enrolled 316 mUC pts who progressed during or following pctx. Pts received atezo at 1200 mg IV q3w until loss of clinical benefit. The SP142 IHC assay centrally assessed PD-L1 expression. Pts/investigators were blinded to PD-L1 status. Co-primary endpoints were confirmed ORR by RECIST v1.1 per central review (IRF) and modified (m) RECIST per investigator, which were met if null hypothesis (ORR = 10%) was rejected (α = 5%). ORR endpoints were stratified by PD-L1 tumor-infiltrating immune cell (IC) status: IC2/3, IC1/2/3, all comers. Results: Efficacy/safety-evaluable pts (N = 311) had a median age of 66 y, CrCl < 60 mL/min (35%) and ≥ 2 prior regimens for mUC (40%). Many had poor prognostic factors (Table). At 5/5/15 data cutoff (follow up ≥ 24 w), 43/47 responding pts had ongoing responses. Both IRF (Table) and mRECIST ORR correlated with IC status. Durable responses were seen including poor prognostic subgroups (Table). mDOR was not reached in any PD-L1 or prognostic subgroup. mPFS was 2.1 mo in all PD-L1 subgroups. Median treatment duration was 12 w (range 0-46). Treatment-related AEs (most commonly fatigue) occurred in 66% of pts (all Grade); 15% had G3-4 related AE and 4% had G3-4 immune-mediated AE. 27% of AEs led to dose interruption and 3% led to withdrawal. No renal toxicity was seen. Conclusions: IMvigor 210, the first Ph 2 study targeting PD-L1/PD-1 in mUC, demonstrated significantly improved ORR vs historic controls. Responses were durable and associated with higher PD-L1 IC expression; poor prognostic factors did not preclude response. Atezo was well tolerated, and a randomized Ph 3 study vs ctx is ongoing (IMvigor 211; NCT02302807). Clinical trial information: NCT02108652. [Table: see text]

Background: Understanding of immune tolerance mechanisms of cancer has prompted the development of cancer immunotherapies such as atezolizumab (anti-PD-L1, MPDL3280A). Robust, durable responses have been observed, leading to Breakthrough status designation by the FDA for atezolizumab for previously treated NSCLC and bladder cancer (UBC) patients. Roche/Ventana have developed a companion diagnostic (CDx) for atezoliziumab using a robust immunohistochemistry (IHC) assay and antibody clone (SP142), optimized to detect PD-L1 expression in both tumor cells (TC) and tumor-infiltrating immune cells (IC). Here we describe the characteristics of the SP142 assay, PD-L1 expression patterns observed by immunohistochemistry in TC and IC compartments, and their association with clinical efficacy for NSCLC and UBC patients. Methods: The anti-human PD-L1 rabbit monoclonal antibody SP142 was optimized for detection of both TC and IC expression of PD-L1 with the Ventana OptiView DAB IHC Detection Kit on the automated BenchMark ULTRA platform. The VENTANA PD-L1 (SP142) CDx assay was validated for use in formalin-fixed, paraffin-embedded samples of NSCLC and UBC in a series of studies addressing sensitivity, specificity, robustness, and precision. Formalin fixed, paraffin embedded tumor specimens were obtained from patients prescreened and/or enrolled into Genentech Ph I study PCD4989g, and PD-L1 expression was measured using the SP142 assay and PCR gene expression assays. Results: The SP142 assay met pre-defined acceptance criteria for TC and IC assessment of PD-L1 expression in NSCLC and UBC tumors, including >90% inter-reader concordance between pathologist readers. Rapid and durable responses were observed in the Ph I study (PCD4989g), and correlated with PD-L1 expression patterns observed by immunohistochemistry in TC and IC. In the same Ph I study (PCD4989g), PD-L1 expression as measured by PCR did not demonstrate the same predictive value as observed for IHC. Conclusions: The PD-L1 IHC (SP142) CDx is a robust assay to measure PD-L1 expression in both IC and TC. Further, the high reproducibility of results between pathologists shows that the scoring algorithms in UBC and NSCLC are precise, reproducible, and practical in the diagnostic setting. The results indicate that favorable atezolizumab efficacy for UBC is strongly associated with higher IC levels as assessed by the sensitive and specific PD-L1 IHC (SP142) CDx assay. In NSCLC, favorable atezolizumab efficacy is associated with tumors expressing either high TC or high IC levels by the PD-L1 IHC (SP142) CDx assay. These data support the predictive value of tumor PD-L1 levels by IHC for NSCLC and UBC patients receiving atezoliziumab. Citation Format: Zachary S. Boyd, Dustin Smith, Brian Baker, Bharathi Vennapusa, Hartmut Koeppen, Marcin Kowanetz, Sanjeev Mariathasan, Jean-Marie Bruey, Howard Mackey, Gregg Fine, Simonetta Mocci, Priti Hegde, J. Andrew Williams, Ian McCaffery. Development of a PD-L1 companion diagnostic IHC assay (SP142) for atezolizumab. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B001.

Background: Programmed death ligand-1 (PD-L1), a ligand for PD-1 and B7.1, is broadly expressed on tumor cells (TC) and tumor-infiltrating immune cells (IC) in many human cancers. PD-L1 expression on either TC or IC can negatively regulate antitumor T-cell function within the tumor microenvironment (TME). Consistent with this, the ORR, PFS and OS benefit of atezolizumab (atezo) across PhI and PhII studies appeared to correlate with increasing baseline PD-L1 expression levels on TC and/or IC. Therefore, we explored the biologic reasons for PD-L1 expression on TC and IC, the association with response to atezo and the intrapatient heterogeneity of PD-L1 expression in NSCLC. Methods: Tumor specimens were obtained from patients (pts) prescreened and/or enrolled in NSCLC atezo trials (PhI PCD4989g, PhII POPLAR and FIR [n=1360]) and from pts treated at MSKCC (n=39). Samples included 14 synchronous and 106 metachronous pairs collected in FIR or at MSKCC. Using the SP142 IHC assay, which has been optimized to detect PD-L1 on both TC and IC, PD-L1 expression was scored at 4 levels (TC0-3 and IC0-3) based on increasing expression. A subset of samples was further characterized by histopathologic review and gene expression by RNAseq. CD8 expression (clone C8/144B) was assessed in the tumor center, invasive margin and periphery by IHC. Results: PD-L1 was expressed on IC only, on TC only or on both TC and IC within the TME. Tumors with the highest (TC3 or IC3), moderate/high (TC2/3 or IC2/3) and any (TC1/2/3 or IC1/2/3) PD-L1 expression represented ≈15%, ≈38% and ≈70% of NSCLC, respectively. PD-L1 expression was similar across all paired synchronous and metachronous tissues. At the TC3 or IC3 cutoff, PD-L1 status remained unchanged in 86% of paired synchronous specimens and in 78% of metachronous pairs. Analysis of PD-L1 expression patterns revealed the existence of exclusive TC and IC subpopulations at each PD-L1 expression level, unique to NSCLC and not seen in other cancers, e.g. UBC. Strikingly, TC3 and IC3 tumors represented 2 distinct populations, with Conclusions: These data demonstrated that NSCLC has unique PD-L1 expression patterns. High expression of PD-L1 on TC and/or IC in NSCLC confers sensitivity to atezo, despite exhibiting distinct immunologic profiles. These results further our understanding of how atezo promotes responses in tumors expressing PD-L1 on TC and/or IC and emphasizes the need to assess PD-L1 on both TC and IC in NSCLC. In addition, intrapatient heterogeneity in PD-L1 expression was relatively low in both synchronous and metachronous tissues, indicating that various types of tumor samples (e.g. primary or metastatic, fresh or archival) can be reliably used to assess PD-L1 expression with the SP142 assay. Citation Format: Marcin Kowanetz, Hartmut Koeppen, Wei Zou, Sanjeev Mariathasan, Matthew Hellmann, Mark Kockx, Colombe Chappey, Edward Kadel, Dustin Smith, Natasha Miley, Vincent Leveque, Roel Funke, Alan Sandler, Ian McCaffery, Lukas Amler, Daniel Chen, Priti Hegde. PD-L1 as a predictive biomarker for atezolizumab (MPDL3280A; anti-PDL1) in non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A017.

Meeting abstracts Atezolizumab (anti-PD-L1) has demonstrated robust clinical activity in UBC [[1][1]]. Elevated PD-L1 expression on tumor-infiltrating immune cells (IC) is associated with increased clinical efficacy; however, the contribution of other immune biomarkers is unknown. In this study, we

541 Background: Biomarker analysis predicting outcome with neoadjuvant atezolizumab in muscle invasive bladder cancer (MIBC) was performed. This includes previously unreported findings with FOXP3 and MHC1. Methods: Sequential tissue obtained from 95 patients in the ABACUSstudy (NCT02662309) which investigated two cycles of atezolizumab prior to cystectomy in MIBC patients. Multiplex immunohistochemistry staining, Foundation One analysis and RNA sequencing was performed on paired pre- and post- treatment samples. CD8+ T cells, fibroblast activation protein (FAP), granzyme – B (GZMB), FOXP3, MHC1, PD-L1 expressions were analyzed and correlated with outcome. Results: After a median follow up of 13.1 months, 31% had a pathological complete response (pCR) and 18% have relapsed. 40% were PD-L1 positive at baseline and 73%, 19% and 8%had inflamed, excluded and desert phenotype respectively. CD8/GZMB and CD8/MHC1 expression prior to therapy was significantly associated with response in inflamed tumors. CD8, PDL1, GZMB and MHC1 expression all increased with treatment in this group of patients. Immune desert phenotype at baseline, showed low and static expression of immune biomarker. TGFb correlated with relapse in excluded phenotypes. Treatment was associated with increase in cell cycle genes and FAP, both of which were associated with relapse. FOXP3 expression correlated with CD8 and increased with therapy in responding tumors. Combining FAP (high) to CD8 (low) and MHC1 (low) increased the positive predictive value for relapse. TMB did not correlate with outcome or increase with therapy. FGF DNA alterations were associated with response. Conclusions: MIBCs have high T effector immune expression, which may account for high pCR rates. Biomarkers at baseline and after treatment can predict outcome. Assessment of multiple biomarker within algorithms improves accuracy in predicting outcome. FOXP3 expression correlates with activated T cell expression, potentially accounting for the counterintuitive findings. Clinical trial information: NCT02662309.