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Patients with metastatic castration-resistant prostate cancer have few treatment options after novel hormonal therapy (eg, abiraterone or enzalutamide). We aimed to evaluate cabozantinib, a tyrosine kinase inhibitor with immunomodulatory properties, in combination with the PD-L1 inhibitor atezolizumab in metastatic castration-resistant prostate cancer.COSMIC-021 is an ongoing, multicentre, open-label, phase 1b study with a dose-escalation stage followed by tumour-specific expansion stages. Expansion cohort 6 in metastatic castration-resistant prostate cancer was enrolled at 42 cancer research centres in France, Italy, the Netherlands, Spain, and the USA. Eligible patients were aged 18 years or older and had metastatic castration-resistant prostate cancer with radiographic soft tissue progression following treatment with either enzalutamide or abiraterone, or both; measurable soft tissue disease per Response Evaluation Criteria In Solid Tumours (RECIST) version 1.1; and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received oral cabozantinib 40 mg per day and intravenous atezolizumab 1200 mg once every 3 weeks. Study treatment continued until progressive disease or unacceptable toxicity. All enrolled patients were assessed for efficacy and safety. The primary endpoint was objective response rate per RECIST version 1.1 as assessed by the investigator. This study is registered with ClinicalTrials.gov, NCT03170960.Between April 24, 2018, and Aug 31, 2020, 132 patients were enrolled and received at least one dose of study treatment. At data cutoff (Feb 19, 2021), median duration of follow-up was 15·2 months (IQR 9·6-21·7). Objective response rate was 23% (95% CI 17-32; 31 of 132 patients), with three (2%) confirmed complete responses and 28 (21%) confirmed partial responses. 72 (55%) of 132 patients had grade 3-4 treatment-related adverse events, with the most common being pulmonary embolism (11 [8%] patients), diarrhoea (nine [7%]), fatigue (nine [7%]), and hypertension (nine [7%]). There was one grade 5 treatment-related adverse event (dehydration). 74 (56%) of 132 patients had serious adverse events of any causality. 28 (21%) of 132 patients had treatment-related adverse events leading to discontinuation of either study drug.Cabozantinib plus atezolizumab showed promising antitumour activity in patients with metastatic castration-resistant prostate cancer after novel hormonal therapy with an acceptable safety profile, supporting further evaluation of this combination.Exelixis.

Supplementary Figure from External Validation of Association of Baseline Circulating Tumor Cell Counts with Survival Outcomes in Men with Metastatic Castration-Sensitive Prostate Cancer

Supplementary Table from External Validation of Association of Baseline Circulating Tumor Cell Counts with Survival Outcomes in Men with Metastatic Castration-Sensitive Prostate Cancer

Patient characteristics

Schematic representation of trial design, patient recruitment, arm assignment, and assignment to endpoint investigations.

Change in alterations across time points

Interim analysis of Grade {greater than or equal to}3 hematologic toxicity in the first 10 patients recruited to the combination arm (radium-223 + enzalutamide).

Trial Protocol

Purpose:The role of circulating cell-free tumor DNA (ctDNA) as an adjunct to tissue genomic profiling is poorly defined in metastatic renal cell carcinoma (mRCC). In this study, we aim to validate previous findings related to genomic alteration (GA) frequency in ctDNA and determine the concordance between ctDNA and tissue-based profiling in patients with mRCC.Experimental Design:Results of 839 patients with mRCC who had ctDNA assessment with a Clinical Laboratory Improvement Amendments (CLIA)-certified ctDNA assay between November 2016 and December 2019 were collected. Tissue-based genomic profiling was collected when available and concordance analysis between blood- and tissue-based testing was performed.Results:ctDNA was assessed in 839 patients (comprising 920 samples) with mRCC. GAs were detected in 661 samples (71.8%). Tissue-based GAs were assessed in 112 patients. Limiting our analyses to a common 73-/74-gene set and excluding samples with no ctDNA detected, a total of 228 mutations were found in tissue and blood. Mutations identified in tissue (34.7%; 42/121) were also identified via ctDNA, whereas 28.2% (42/149) of the mutations identified in liquid were also identified via tissue. Concordance between ctDNA and tissue-based profiling was inversely related to the time elapsed between these assays.Conclusions:This study confirms the feasibility of ctDNA profiling in the largest mRCC cohort to date, with ctDNA identifying multiple actionable alterations. It also demonstrates that ctDNA and tissue-based genomic profiling are complementary, with both platforms identifying unique alterations, and confirms that the frequency of unique alterations increases with greater temporal separation between tests.

Purpose:Radium-223 is approved for metastatic castration-resistant prostate cancer (mCRPC) based on improved overall survival, and delay in skeletal related events. However, it is not associated with PSA or radiographic response, which poses a challenge in real-time assessment of its efficacy. Surrogate markers of treatment outcomes may facilitate tailoring treatment duration with radium-223, by limiting the duration of therapy with radium-223 in these patients. Here, we sought to investigate the utility of bone metabolic markers (BMMs) as surrogate markers of response to radium-223 in mCRPC.Patients and Methods:A prospective phase II trial of radium-223 plus enzalutamide (RE) versus enzalutamide alone was designed to assess surrogacy of BMMs with respect to response to radium-223. Enzalutamide was used as a comparator in lieu of placebo due to the progressive disease. Co-primary endpoints were relative change in serum BMM N-telopeptide (NTP) levels from baseline to 6 months between the two arms and safety and feasibility of the combination.Results:Thirty-nine men were randomized to RE (n = 27) or enzalutamide (n = 12). Combination was safe and feasible. Primary endpoint was met. A statistically significant relative change to NTP ratios between arms (0.64, 95% confidence interval, 0.51–0.81; P = 0.00048) favored RE versus enzalutamide. Overall, BMMs decreased with the RE therapy compared with enzalutamide. Improved PSA response rate in RE versus enzalutamide (P = 0.024), correlated with decline in BMMs.Conclusions:BMMs declined significantly with combination therapy, and were associated with improved outcomes. Upon external validation, BMMs may emerge as surrogate markers to monitor treatment with radium-223 in real-time.

Supplemental Table 1

Purpose:PARP inhibitors (PARPi) are efficacious in multiple cancers harboring germline (and possibly somatic) BRCA1/2 mutations. Acquired reversions can restore BRCA1/2 function, causing resistance to PARPi and/or platinum-based chemotherapy. The optimal method of identifying patients with germline, somatic, and/or reversion mutations in BRCA1/2 has not been established. Next-generation sequencing (NGS) of cell-free DNA (cfDNA) provides a platform to identify these three types of BRCA1/2 mutations.Experimental Design:Patients with advanced breast, ovarian, prostate, or pancreatic cancer were tested using a clinically validated 73-gene cfDNA assay that evaluates single-nucleotide variants and insertion–deletion mutations (indels) in BRCA1/2, and distinguishes somatic/reversion from germline mutations with high accuracy.Results:Among 828 patients, one or more deleterious BRCA1/2 mutations were detected in 60 (7.2%) patients, including germline (n = 42) and somatic (n = 18) mutations. Common coexisting mutations included TP53 (61.6%), MYC (30%), PIK3CA (26.6%), BRAF (15%), and ESR1 (11.5%). Polyclonal reversion mutations (median, 5) were detected in 9 of 42 (21.4%) germline BRCA1/2-mutant patients, the majority (77.7%) of whom had prior PARPi exposure (median duration, 10 months). Serial cfDNA demonstrated emergence of reversion BRCA mutations under therapeutic pressure from initial PARPi exposure, which contributed to subsequent resistance to PARPi and platinum therapy.Conclusions:cfDNA NGS identified high rates of therapeutically relevant mutations without foreknowledge of germline or tissue-based testing results, including deleterious somatic BRCA1/2 mutations missed by germline testing and reversion mutations that can have important treatment implications. Further research is needed to confirm clinical utility of these findings to guide precision medicine approaches for patients with advanced malignancies.

Time to nadir for BMMs and PSA.

Background Combination immunotherapy is now considered the standard first-line therapy for patients with metastatic clear cell renal cell carcinoma (mccRCC) after multiple clinical trials demonstrated improved overall survival compared with single-agent tyrosine kinase inhibitors. Cabozantinib modulates critical components of the immune system, such as decreasing regulatory T cells and increasing T-effector cell populations, and is approved for the treatment of mRCC. Avelumab is a human IgG1 monoclonal antibody that binds to programmed death-ligand 1 protein and inhibits the interaction with PD-1. This phase I trial assessed the safety and clinical activity of avelumab and cabozantinib combination therapy in mccRCC. Methods This study was a phase I, 3+3 dose escalation clinical trial. The primary endpoint was the safety and identification of the recommended phase II dose (RP2D). Secondary endpoints included objective response rate (ORR) and radiographic progression-free survival (rPFS). There were 3 dose cohorts: cabozantinib 20, 40, and 60 mg/day, each combined with avelumab (10 mg/kg intravenously every 2 weeks). An additional 3 patients were included in the final dose cohort as a confirmation of the RP2D. No dose modifications were allowed for avelumab, but dose delays were permitted. Both dose reductions and holds were allowed for cabozantinib. Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, was used to determine ORR, and treatment beyond progression was allowed. Results Twelve patients with newly diagnosed mccRCC were enrolled from July 2018 until March 2020. Three patients were enrolled in the 20 and 40 mg cohorts each, and 6 were enrolled in the 60 mg cohort. The International Metastatic RCC Database Consortium (IMDC) risk categories for these patients were: 4 patients (favorable risk), 6 patients (intermediate risk), and 2 patients (poor risk). No dose-limiting toxicities (DLTs) were observed in any cohort. Six patients developed serious adverse events related to study treatment after the DLT window period. Immune-related adverse events (iRAEs) were reported in 11 patients; fatigue and diarrhea were the most common (each with n = 4, 33.3%), followed by maculopapular rash and hand-foot syndrome (each with n = 3, 25%). Dose reductions were required in 5 of 6 patients in the cabozantinib 60 mg cohort after the DLT period. One patient discontinued avelumab due to irAE (nephritis), while none discontinued cabozantinib due to toxicity. The ORR was 50%, with one complete response (CR) and 5 partial responses (PR). The disease control rate (CR + PR + stable disease) was noted in 92% of the patients. Radiological PFS survival rate at 6 and 12 months was reported in 67.7% and 33.5% of patients, respectively. Conclusion Combination therapy with avelumab and cabozantinib is safe and showed preliminary clinical activity in mccRCC. Even though the DLT was not met in any of the 3 cohorts, the recommended RP2D dose for the combination is cabozantinib 40 mg/day due to a high incidence of grade 2 toxicity for cabozantinib 60 mg/day after the DLT period. (ClinicalTrials.gov Identifier: NCT03200587)

Purpose of Review Historically, kidney cancer was diagnosed as either clear cell renal carcinoma (ccRCC) or non-clear cell renal carcinoma (nccRCC). With further research into the pathophysiology of nccRCC, multiple distinct subtypes have emerged creating distinct diagnosis, such as papillary renal cell carcinoma (PRCC), chromophobe renal cell carcinoma (crRCC), or unclassified carcinoma (cRCC). Many other kidney cancer subtypes are now included in the WHO classification system. Recent Findings The prognosis for each of the more frequently diagnosed types is discussed here along with treatment recommendations. The available clinical trial results and salient retrospective studies of each subtype are reviewed here to guide clinicians on the optimal treatment selection for patients with these rare histologic types or RCC. Summary Many nccRCC types are now recognized and each has unique molecular drivers which are different than ccRCC. The optimal treatment strategy is different for each subtype. The prognosis also differs based on the histology.

BACKGROUND: Patients with von Hippel–Lindau (VHL) disease have a high incidence of renal cell carcinoma owing to VHL gene inactivation and constitutive activation of the transcription factor hypoxia-inducible factor 2α (HIF-2α). METHODS: In this phase 2, open-label, single-group trial, we investigated the efficacy and safety of the HIF-2α inhibitor belzutifan (MK-6482, previously called PT2977), administered orally at a dose of 120 mg daily, in patients with renal cell carcinoma associated with VHL disease. The primary end point was objective response (complete or partial response) as measured according to the Response Evaluation Criteria in Solid Tumors, version 1.1, by an independent central radiology review committee. We also assessed responses to belzutifan in patients with non–renal cell carcinoma neoplasms and the safety of belzutifan. RESULTS: After a median follow-up of 21.8 months (range, 20.2 to 30.1), the percentage of patients with renal cell carcinoma who had an objective response was 49% (95% confidence interval, 36 to 62). Responses were also observed in patients with pancreatic lesions (47 of 61 patients [77%]) and central nervous system hemangioblastomas (15 of 50 patients [30%]). Among the 16 eyes that could be evaluated in 12 patients with retinal hemangioblastomas at baseline, all (100%) were graded as showing improvement. The most common adverse events were anemia (in 90% of the patients) and fatigue (in 66%). Seven patients discontinued treatment: four patients voluntarily discontinued, one discontinued owing to a treatment-related adverse event (grade 1 dizziness), one discontinued because of disease progression as assessed by the investigator, and one patient died (of acute toxic effects of fentanyl). CONCLUSIONS: Belzutifan was associated with predominantly grade 1 and 2 adverse events and showed activity in patients with renal cell carcinomas and non–renal cell carcinoma neoplasms associated with VHL disease. (Funded by Merck Sharp and Dohme and others; MK-6482-004 ClinicalTrials.gov number, NCT03401788.)

Poly (ADP-ribose) polymerase (PARP) inhibitors are approved for patients with metastatic castration-resistant prostate cancer harboring deleterious or suspected deleteriousSomatic genomic profiling results were obtained from a clinical cohort of patients at our institution who had at least two samples tested. One of the samples needed to be from either primary or metastatic tissue. Concordance was adjusted to not include mutation types that the cfDNA platforms were not designed to detect.The presence or absence of mutations in theThere is a high level of concordance between tissue and blood for

133 Background: In the PEACE-1 trial (Fizazi, ESMO 2021), in pts with dn-hv-mCSPC, the addition of abiraterone to ADT + docetaxel (triplet therapy arm) resulted in a median OS of 61 months (OS on ADT + docetaxel arm was 42 months). However, independent contribution of docetaxel to efficacy of ADT + abiraterone in the triplet therapy arm of PEACE-1 trial is not clear. Furthermore, the efficacy of an novel hormonal therapy (NHT) specifically in dn-hv-mCSPC population has not been reported (LATITUDE trial’s eligibility did not include volume status). Herein, our objective was to assess PFS and OS in a cohort of dn-hv-mCSPC pts undergoing intensified ADT with either NHT (i.e. novel androgen receptor or androgen synthesis inhibitors) or docetaxel. Methods: In this IRB-approved study, patient-level data were collected retrospectively. Eligibility: presence of dn-hv-mCSPC (hv per CHAARTED criteria) undergoing intensified ADT with either NHT or docetaxel started within 3 months of diagnosis. Study endpoints: PFS was calculated per PCWG-2 - defined PSA progression or radiographic progression or clinical progression whichever occurred first; OS was defined as start of therapy to date of death or censored at last follow-up. A multivariate analysis using the Cox proportional hazards (Cox-ph) model was used; the relationship between treatment intensification with both PFS and OS was assessed and adjusted for age at diagnosis, Gleason score, presence of visceral metastases, and PSA at baseline. Results: 85 pts with dn-hv-mCSPC were included: 45 received ADT + NHT; 40 received ADT + docetaxel. In the NHT vs docetaxel arms: median PFS were 23 vs 14 months; and median OS were 63 vs 36 months respectively. See the table for Cox-ph and adjusted co-variate results. Conclusions: We for the first-time report the real-world survival outcomes with ADT + NHT specifically in pts with dn-hv-mCSPC. In addition, in these hypothesis-generating data, the OS of pts with dn-hv-mCSPC undergoing ADT + NHT or ADT + docetaxel were similar to those in the triplet therapy arm or ADT + docetaxel arm of PEACE-1 trial respectively. A randomized trial in pts with dn-hv-mCSPC comparing ADT + NHT vs triplet therapy may better characterize the benefit of the docetaxel component in the triplet therapy.[Table: see text]

5080 Background: Pts with DN-mCSPC have been reported to experience worse prognosis and outcomes compared to those with PLT-mCSPC. We hypothesized that gene expression profiling of pre-treatment primary prostate tumors from PLT-mCSPC pts would be distinct from those with DN-mCSPC. Methods: Eligibility criteria: histologically confirmed mCSPC and available RNAseq profiling performed by a CLIA certified lab using primary prostate biopsies collected prior to start of treatment. Pts were categorized into two cohorts: PLT-mCSPC versus DN-mCSPC. The DEseq2 pipeline was used to analyze differentially expressed genes between the groups. The data included the Log2 fold change, Wald-Test p-values, and Benjamini-Hochberg adjusted p-values for each differentially expressed gene. These results were subjected to Gene Set Enrichment software analysis (GSEA) in order to identify pathways enriched in each cohort. All bioinformatic analysis was undertaken using R v4.2. Results: Ninety-seven (97) patients met eligibility (52 PLT, 45 de novo). Characteristics of the overall eligible pts: median age = 65, median baseline PSA = 12.6, Gleason score ≥8 = 71%, and high volume of disease = ̃30%. Differential expression and pathway enrichment between cohorts: upregulation of cell-cycle signaling pathways (G2-M checkpoint, E2F) in pts with DN-mCSPC, and upregulation of androgen signaling and immune pathways (inflammatory response, NFKB-mediated TNF-alfa signaling) in pts with PLT-mCSPC (Table). Conclusions: These hypothesis-generating data, upon external validation, may provide the rationale for personalized therapy in men with mCSPC, such as the use of CDK4/6 inhibitors in addition to standard of care intensified ADT in men with DN-mCSPC. [Table: see text]

INTRODUCTION: Metastatic prostate cancer is a heterogeneous disease characterized by clinical and genomic heterogeneity. Many prostate cancers harbor mutations causing DNA repair deficiency, specifically homologous recombination deficiency, sensitizing to drugs that inhibit poly ADP-ribose polymerase (PARP). PARP is an enzyme that is involved in single-stranded DNA repair and is the target of newly approved treatments for metastatic prostate cancer. AREAS COVERED: Here, the authors’ review the clinical trials leading to the recent approvals of two PARP inhibitors (PARPi), olaparib and rucaparib, specifically TOPARP-A, TOPARP-B, PROfound and TRITON-2. They also compare the different FDA approvals for both of these medications and outline the safety of this class of drugs in prostate cancer. EXPERT OPINION: Because PARPi are particularly effective in men with somatic or germline alterations in BRCA1 and BRCA2, we recommend that all men be tested for DNA alterations with next-generation sequencing in tumor cells obtained from either tissue or blood. We also recommend that olaparib or rucaparib be considered relatively early in the treatment sequence in metastatic castration-resistant prostate cancer patients with BRCA1 or BRCA2 mutations. Other DNA alterations might also sensitize to PARPi though the response rates are lower, so other standard therapies should be prioritized first.

233 Background: In general, older pts are likely to have an advanced stage PCa, hence poor overall survival (PMID: 18660852). Owing to increased awareness and better diagnostics, the incidence of PCa has steadily increased amongst older adolescents and young adult pts (PMID: 31553489). Recent reports suggest that younger pts often are staged less adequately, present with more advanced stages, and could have worse outcomes than older pts (PMID: 33575208). Hence, elucidating the underlying molecular biology of PCa by age may unravel specific biologic features and distinct genomic expressions specific to young-age PCa, and help investigate new therapeutic targets. Methods: In this IRB-approved retrospective study, eligibility criteria included pts diagnosed with advanced PCa with available tumor-based comprehensive transcriptomic profiling from a CLIA-certified lab. DeSeq2 analysis was implemented in Bioconductor software to analyze differentially expressed genes based on the cohort's age cut-off points (< 65 vs. ≥65 years). DeSeq2 results included the Log2 Fold change, Wald-Test p-values, and Benjamini-Hochberg adjusted p-values for each differentially expressed gene. These results were then subjected to Gene Set Enrichment Analysis (GSEA) to identify pathways upregulated or downregulated in each cohort. All bioinformatic analysis was conducted in R-Studio, version 4.1.1. The statistical significance level was predetermined at 0.05. Results: 80 pts were eligible: < 65 (n=44) vs ≥65 years (n=36). No differences in Gleason score (

105 Background: In clinical trials, treatment efficacy rates are based on participants who can tolerate treatment through study endpoints. Attrition from clinical trials can potentially lead to biased results (PMID: 30379822). Many oncology clinical trials censor the subject data of participants because of early trial intervention discontinuation due to adverse events (AEs), withdrawal of consent, or loss to follow-up. Despite high attrition rates reported across various oncology clinical trials (10-38%), there is inconsistency regarding investigating the reasons for withdrawal (PMID: 23132290). We aim to identify the causes of the withdrawal of participants with advanced PCa from clinical trials. Methods: In this IRB-approved single-center retrospective study (Sept 2014 to Sept 2022), the OnCore Research Database was used to capture data on the participants with advanced PCa enrolled in clinical trials. The included trials were specific to prostate cancer, and mixed solid tumor trials were excluded. Endpoint reports from all included trials were assessed. Participants who discontinued treatment for any reason were included. The primary objective was to obtain reasons for clinical trial withdrawal before primary endpoints, identify potential clinical intervention areas, and determine potential areas of adjustment to future study designs to improve retention rates. Eligibility criteria: diagnosis of metastatic prostate cancer, receipt of protocol treatment until discontinuation, and documentation of a reason for discontinuation of the protocol treatment. Results: 272 pts from the 18 clinical trials met eligibility criteria and were included in the study. The most common reasons documented for discontinuation were: the progression of disease (46.69%), other reasons (15.44%), adverse events (5.15%), personal preference (15.81%), and completion of protocol treatment (11.76%) of the total number of enrolled participants. We noted a statistically significant difference between participants who withdrew for other reasons in the castration-resistant versus castration-sensitive setting (6.08% vs. 32.38%, p value=0.03). Notably, declining performance status and symptom progression were listed under the “other reasons” category. The documentation of patient withdrawal due to clinical symptoms was reported across multiple withdrawal categories. Conclusions: In approximately one-third of participants, the reason for protocol treatment discontinuation was not apparent (documented as patient preference and other reasons with no further specifications). Further exploration of the exact reasons contributing to therapy discontinuation in these patients will be critical to improving patient retention in clinical trials.

231 Background: Increased Body Mass Index (BMI) has been linked to increased prostate cancer incidence, recurrence, and mortality (PMID: 35538398). Herein, we sought to investigate the underlying differences in gene expression profiles based on BMI in patients (pts) with PCa. Methods: In this IRB-approved retrospective study, eligibility criteria included histologically confirmed PCa and available RNA sequencing results from treatment naïve primary prostate tissue by a CLIA-certified lab. Pts were categorized into two cohorts: obese (Ob, BMI≥30) and non-obese (non-Ob, BMI

726 Background: VTE is a common complication in pts with mRCC. Identifying pts with mRCC at the highest risk of developing VTE may provide the rationale for initiating prophylactic anticoagulation. Methods: In this IRB-approved retrospective study, pts diagnosed with mRCC between 7/2012 and 7/2022 at Huntsman Cancer Institute at University of Utah were included. Variables evaluated were pts' clinical characteristics, treatment, and anticoagulation therapy. Pts with mRCC with VTE within 12 months after diagnosis were used as cases and those without VTE during the same period were used as control. The multivariable logistic model was used to assess risk factors of VTE. DeSeq2 analysis was implemented in Bioconductor Software to analyze differentially expressed genes based on the VTE. These results were subjected to gene ontology analysis in the TopGO software. All bioinformatic analysis was conducted in R-Studio, version 4.1.1. Results: Among 355 pts with mRCC, 53 pts developed VTE within 12 months after diagnosis (incidence rate: 14.9%). Pts of the two groups (with or without VTE) did not differ significantly when compared for age, gender, race, cytoreductive nephrectomy rate, clear cell histology, grade of tumor, IMDC risk factors (table). Pts who developed VTE had a higher BMI at diagnosis (31.7 vs. 29.1 kg/m2, p=0.03). In multivariate analysis, obesity (OR=1.06, [1.01-1.12], p=0.028) was associated with increased VTE risk. There was no significant difference of mutation rates in genomic panel. Transcriptomic analysis showed hormone metabolic, organic acid transport, extracellular matrix and structure organization (all p

234 Background: Pts with mCSPC receiving i-ADT and achieving a PSA nadir ≤0.2 ng/mL (PSA-L) demonstrate significantly better overall survival (OS) as compared to those with a PSA nadir > 0.2 ng/mL (PSA-H) (Chi AUA 2021, Saad ASCO 2022). We hypothesized that tumor gene expression profile would differ between PSA-L and PSA-H. Methods: In this IRB-approved retrospective study, eligibility criteria included confirmed mCSPC receiving i-ADT with androgen receptor-axis-targeted therapy (ARAT) and availability of RNAseq profiling performed by a CLIA-certified lab of primary prostate biopsies collected before treatment. Pts were divided into 2 groups: PSA-L and PSA-H based on achieving a PSA nadir ≤0.2 ng/mL at any time during treatment course. The DEseq2 pipeline was used to analyze differentially expressed genes between the groups. The data included the Log2 fold change, Wald-Test p-values, and Benjamini-Hochberg adjusted p values (q values) for each differentially expressed gene. These results were subjected to Gene Set Enrichment Analysis (GSEA) to identify pathways enriched in each cohort. All bioinformatic analysis was undertaken using R studio v4.2. Results: 78 pts were eligible: 55 were PSA-L, and 23 were PSA-H. The most significantly upregulated pathways in PSA-L were the TNFA signaling, androgen response (AR), estrogen response, and interferon-alpha response pathways. The most upregulated pathways in PSA-H were epithelial-mesenchymal transition, coagulation, and bile acid metabolism pathways. Normalized enrichment scores are reported in the table. Differential individual gene expression profiles will be presented at the meeting. Conclusions: These hypothesis-generating data show that mCSPC pts on i-ADT with PSA-L have distinct baseline tumor gene expression profiles, such as upregulation of AR signaling, compared to pts with PSA-H. After external validation, these findings may help personalize medicine prior to initiation of therapy in pts not expected to achieve PSA-L. [Table: see text]

364 Background: Prostate cancer (PCa) patients (pts) with DNA repair defects (aka “BRCAness”) generally have more aggressive disease and a worse overall prognosis compared to men without BRCAness (PMID: 33781305). Biochemical recurrence (BCR) develops in almost one-third of men with PCa after treatment with local therapy. We hypothesized that treatment with rucaparib monotherapy in men with systemic treatment naïve high-risk nmHSPC would result in acceptable disease control, allow a delay of androgen deprivation therapy (ADT) and the onset of metastasis. Methods: This is a single-arm, open-label, phase II trial; eligibility criteria: (1) Histologically proven prostate adenocarcinoma, presence of one of the following alterations in (by soft tissue or liquid biopsy): BRCA1, BRCA2, ATM, BARD1, BRIP1, CHEK1, CHEK2, FANCA, NBN, PALB2, RAD51C, RAD51D, RAD51, RAD51B, (2) No radiographic evidence of metastatic disease by conventional scans (3) PSA doubling time of ≤10 months. The primary endpoint: PSA progression-free survival (PSA-PFS). Secondary endpoints: safety, the proportion of pts with a PSA 50% response (PSA50), and an undetectable PSA. Results: Seven pts were enrolled in the study with the following pathogenic alterations: ATM (n=3), BRCA2 (n=2), BRCA1 (n=1), BRIP1 (n=1), RAD51(n=1), and received treatment with rucaparib at 600 mg twice daily. A 4-week treatment duration comprised one cycle. The median duration of follow-up was 18 months. A median of 20 cycles (range 4-42) was completed, median PSA-PFS was 35.37 months (95% CI: 0 - 85.11 months). 2/7 patients achieved PSA50; both had nadir PSA as undetectable. Grade ≥ 3 adverse events (AEs) were anemia and rash (in 1 pt each). No dose-limiting toxicities or severe AEs were seen. The study was prematurely terminated in June 2022 after the accrual of 7 pts because next-generation scans (e.g., PSMA-PET) became the standard of care for pts with BCR. Conclusions: Rucaparib demonstrated acceptable toxicity and preliminary efficacy in pts with PCa with BCR. Gene alteration-specific efficacy will be presented in the meeting. Limitations: Small cohort, no comparison arm. Hence results should be interpreted cautiously but generally consistent with larger prospective trials of PARP inhibitors. Clinical trial information: NCT03533946 . [Table: see text]

TPS739 Background: The landscape for treatment of metastatic renal cell carcinoma (mRCC) has changed dramatically over the past 7 years with the approvals of tyrosine kinase inhibitors and immune-oncology (IO) agents alone or in combination for untreated mRCC. However, multiple knowledge gaps remain. While active surveillance remains an option for selected pts, prospective evidence on selection of and outcomes for pts is limited. Recent phase III trials all used a common comparator, sunitinib, so no comparative effectiveness data on the new IO-based regimens exists. There are also no routinely used predictive biomarkers in mRCC pt management. Therefore, a better understanding of the biologic determinants associated with cancer heterogeneity and clinical outcomes through blood, tumor, and radiographic based assessments is needed. Importantly, longitudinal changes in health-related quality of life (QOL) and symptom burden of patients with mRCC initiated on new IO–based regimens outside of an interventional clinical trial are poorly understood. Pt reported outcomes (PRO) are rarely captured in a systematic manner. Addressing the evidence gap for how real world pts symptomatically change with treatment combinations and sequences over time is a pressing unmet need. Methods: This is a prospective, observational cohort, phase IV study of 800 mRCC pts in the US. Pts must: be age ≥19 at informed consent; have a diagnosis of mRCC (any histology) with no prior systemic therapy for mRCC (surgery and radiation therapy, prior neoadjuvant/adjuvant therapy for non-mRCC, and pts currently not on systemic therapy and being observed are all permitted); and be able to comply with completion of PROs. Those being treated for active malignancies other than mRCC or not intending to undergo follow up care at a study site within PCORnet are excluded. Pts will undergo consent and baseline assessments, including research blood collection and processing, by the study site team. A novel aspect of this study is the use of PCORnet and Medicare data to minimize data collection burden on sites. PCORnet, the National Patient-Centered Clinical Research Network, is a network of networks that curates EHR data from multiple health systems using a common data model. This allows subsequent follow up to be centrally coordinated by the coordinating center. PRO will be collected at baseline (pre-treatment), every 3 mos for 2 yrs, and then every 6 mos until end of follow up (minimum 18 mos follow-up; maximum 36 mos follow-up). The primary objective is to determine distinct patterns of change in QOL and symptom burden of mRCC pts receiving therapy. Secondary objectives include quantifying the time to treatment discontinuation of pts, identifying patterns of clinical management in the real world setting of mRCC pts on various treatment regimens, and evaluating overall survival of mRCC pts. ClinicalTrials.gov Identifier: NCT04919122 Clinical trial information: NCT04919122 .

244 Background: Pre-existing DM is associated with increased PCa specific and all-cause mortality in men with prostate cancer (PMID: 27652121). However, the underlying reasons are unclear. We hypothesized that transcriptomic profile of metastatic PCa pts with diagnosis of DM prior to the diagnosis of metastatic disease and start of systemic therapy will be different from those without DM. Methods: In this IRB-approved retrospective study, advanced PCa pts with available RNA profiling of treatment naïve tumor tissue through a CLIA-certified laboratory were included. Based on pre-existing DM prior to onset of metastatic disease, pts was grouped into DM and non-DM. Differential gene expression analysis between the two groups was performed using DeSeq2. These results were subjected to Gene Set Enrichment software analysis (GSEA) to identify pathways enriched in each cohort. Gene ontology analysis using TopGO software was done to identify the biological process occurring at the molecular level of these differentially expressed genes. All bioinformatic analysis was conducted in R studio, version 4.1.1. Results: 75 pts were eligible and included: 20 DM vs 55 non-DM. Baseline characteristics (DM vs non-DM): median age 63.5 vs 64 years; median PSA at diagnosis 20 vs 18.85ng/mL; de novo disease: 55% vs 43.6%; Gleason score ≥8: 60% vs 74.5%. DM pts had upregulation of the following pathways: TNF alpha signaling, inflammatory response, IL-6 JAK STAT3 signaling, heme metabolism, and the p53 pathway vs non-DM pts. Gene ontology analysis and individual differential gene expression profiles will be reported at the meeting. Conclusions: Our study found that pre-existing DM is associated with upregulation of inflammatory pathways in pts with PCa These hypothesis-generating results need external validation. Identification of transcriptomic biomarkers in these subsets of pts may help with further drug development. [Table: see text]

561 Background: Understanding the influences of cigarette smoke exposure at the gene expression level may have clinical significance and therapeutic implications. Investigating variations in the gene expression patterns could provide insights into differences in disease progression, survival, and therapeutic response based on smoking history amongst smokers vs. non-smokers (PMID: 29050337). Our objective was to correlate smoking with the gene expression of pts with locally advanced or metastatic UC. Methods: In this IRB-approved retrospective study, eligibility criteria included pts with locally advanced or metastatic UC with available tumor-based comprehensive transcriptomic profiling from a CLIA-certified lab. DeSeq2 analysis was implemented in Bioconductor software to analyze differentially expressed genes based on smoking history. DeSeq2 results included the Log2 Fold change, Wald-Test p-values, and Benjamini-Hochberg adjusted p-values for each differentially expressed gene. These results were then subjected to Gene Set Enrichment Analysis (GSEA) to identify pathways upregulated or downregulated in each cohort. All bioinformatic analysis was conducted in R-Studio, version 4.1.1. Statistical significance was predetermined at p < 0.05. Results: 38 pts were eligible and included: Smokers (n=18) and non-smokers (n=20). The median age at diagnosis for smokers vs. non-smokers (67 vs.71 years). The three most upregulated significant pathways amongst smokers (vs. non-smokers) were the MYC, E2F target, and cholesterol homeostasis pathways (q for all

TPS294 Background: EV, an antibody-drug conjugate (ADC), consists of a fully human antibody directed against the extracellular domain of Nectin-4 (N4), which is conjugated to a microtubule-disrupting agent, monomethyl auristatin E (MMAE), by a protease-cleavable linker. MMAE disrupts tubulin polymerization leading to mitotic arrest and apoptosis. N4 RNA is expressed in prostate tissue, but its expression levels in mCRPC are currently unknown. In animal models of prostate, metastatic lesions showed a very high (++++) membranous N4 expression and correlated with advanced disease (PMID: 30767361). In prostate cancer cell lines engineered to express N4 (PC3-Nectin-4), the hybridoma version of EV: AGS-22M6E, demonstrated potent dose-dependent cytotoxicity (PMID: 27013195). MMAE destabilizes microtubules in contrast to stabilization by taxanes and has shown anti-tumor activity in taxane refractory cell lines and in mCRPC pts with prior taxane therapy (PMID: 31742767). We initiated a phase 2 trial of EV in pts with mCRPC. Methods: This IRB approved, investigator-initiated, single-arm, single-center, non-randomized, open-label study will enroll 34 pts. EV will be administered at 1.25 mg/kg IV on days 1, 8, and 15 of 28- day cycle. Key eligibility criteria: ≥18 years age, mCRPC with histologically/cytologically confirmed adenocarcinoma without small cell histology, ECOG performance status ≤ 1, adequate organ function, prior treatment with ≥3 cycles of docetaxel, at least one androgen-receptor axis targeting agent, received/refused all therapies shown to improve overall survival (OS) except cabazitaxel which is exclusionary. Primary objective: To assess the antitumor activity of EV as determined by one of the following: objective response by RECIST 1.1, confirmed conversion of circulating tumor cell count (CTC) to 0) that true response rate (RR) is 25% will be tested against a one-sided alternative. In first stage if ≤3 responses are observed of 11 pts, the study will be stopped. Otherwise, 23 additional pts will be accrued (total 34). H0 will be rejected if ≥13 responses are observed in 34 pts. This design yields type I error rate of 0.046 and power of 0.854 when true RR is 50%. Secondary endpoints: safety, tolerability, progression-free survival (radiological, clinical and PSA), OS, duration of PSA50% response, CTC conversion rate from ≥5/7.5 ml at baseline to

TPS295 Background: Preclinical studies and clinical observations suggest that C promotes an immune permissive environment, which might lead to synergistic effects from combination treatment with immune checkpoint inhibitors. In Cohort 6 of COSMIC-021 study, the combination of C and A showed encouraging clinical activity and acceptable tolerability in mCRPC pts who had radiographically progressed in soft tissue on or after novel hormonal treatment (NHT; PMID: 35690072). CONTACT-02 is a phase 3 study randomizing pts with mCRPC with measurable disease 1:1 to C+A or NHT (NCT04446117). The objective of this study is to specifically evaluate the safety and efficacy of C+A in pts with mCRPC with NMD. Methods: AtezoCab is an IRB approved, investigator-initiated, single-arm, single-center, open-label, non-randomized phase 2 study of C+A in mCRPC patients with NMD to assess disease control rate (DCR). Treatment: C 40 mg oral daily + A 1200 mg intravenously every 3 weeks. Treatment continues until progression or intolerable toxicities. Key inclusion criteria: ≥18 years age, mCRPC with histologically or cytologically confirmed adenocarcinoma without small cell histology, Eastern Cooperative Oncology Group performance status ≤ 2, adequate organ function, prior treatment with NHT, only NMD outside the pelvis (above aortic bifurcation) per RECIST 1.1 criteria. Key exclusion criteria: prior chemotherapy for mCRPC, prior treatment with C, immune checkpoint inhibitors or other systemic immunostimulatory agents, active or history of clinically significant autoimmune disease per treating physician, corticosteroids (> 10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days before first dose of study treatment. Primary endpoint: Percentage of pts with disease control. DCR will be defined as the percentage of pts with confirmed response of any duration or stable disease or noncomplete response or nonprogressive disease for 24 weeks or longer per PCWG3-modified RECIST v1.1. Up to 33 pts will be enrolled for a total of 30 evaluable pts. This will ensure that DCR can be estimated via a 95% confidence interval (CI) with margin of error

235 Background: GS is the most powerful prognostic predictor in prostate adenocarcinoma. However, the underlying reasons of disease aggressiveness as a function of GS are currently unknown. Herein we sought to investigate the corresponding differences in gene expression profiles of pts with prostate adenocarcinoma with respect to GS. Methods: In this IRB approved retrospective study, eligibility criteria included histologically confirmed prostate adenocarcinoma and available RNA sequencing results from treatment naïve primary prostate tissue by a CLIA certified lab. Pts were categorized into two cohorts: low GS (GS

156 Background: We hypothesized that treatment with Radium-223 (Ra223) and to ≤5 sites of bony metastases (mets) could safely delay the time to start androgen deprivation therapy (ADT) and maintain quality of life (QoL). Methods: 20 men previously treated with surgery, radiation, or both for M0 PCa later developed ≤5 bone-only mets were eligible for this prospective trial. Inclusion: testosterone ≥ 100 ng/dL and mets on conventional bone scan, validated by a CT, MRI, or PET/CT. Exclusion: LHRH therapies after initial treatment, or N1 disease at diagnosis of bone mets. Therapy was 6 cycles of Ra223 and SBRT (30 Gy in 5 fractions between cycles 1-2). Bone scan was performed at baseline and q3 months. PSA was evaluated monthly during the Ra223 course, and q3 months after. Therapeutic effectiveness was defined as ≥20% of patients meeting the primary endpoint of freedom from ADT (FFAdt) use at 15 months. Discontinuation of study therapy occurred if: PSA rise > 10% if baseline PSA >20ng/ml, PSA>20 if baseline PSA 1/2 standard deviation from the mean baseline value and were censored after the time of ADT use. Continuous and categorical covariates were compared using the Wilcoxon rank sum and Pearson’s Chi2 tests, respectively, and univariate Cox regression. Statistical significance was considered at P0.05). Conclusions: First-line use of Ra223 and SBRT to oligomets in hormone-naïve men in this prospective pilot study resulted in a significant delay in ADT use compared to historical control, is well tolerated, and maintains QoL. Clinical trial information: NCT03304418 .

559 Background: BLASST-1 is multi-center phase II trial evaluating neoadjuvant nivolumab (N) with gemcitabine-cisplatin (GC) for patients (pts) with MIBC undergoing radical cystectomy (RC) (NCT03294304). 41 pts with MIBC (cT2-T4a, N≤1, M0) were enrolled between Feb 2018 and June 2019; (cT2N0 90%, cT3N0 7%, cT4N1 3%). Pts received C (70mg/m2) IV on D1, G (1000mg/m2) on D1, D8 and N (360 mg) IV on D8 every 21 days for 4 cycles followed by RC within 8 wks. Primary endpoint was pathologic down staging (PaR; ≤pT1N0). Safety, Relapse-free survival (RFS), Progression-free survival (PFS) and biomarker analyses were secondary endpoints. PaR rate was 65.8%, pCR (≤pT is N0) rate was 49% and there were no safety concerns or delays to RC. At a median follow-up of 15.8 mos, 12-month RFS rate was 85.4% and PFS including death from any cause was 83%. We now report correlation of PaR with tumor mutation patterns of responders (R) and non-responders (NR) using Whole Genome Sequencing (WGS). Methods: DNA was extracted from pre-treatment tumor samples and sequenced to an average depth of 150X and DNA extracted from matched normal tissue (peripheral blood) to a mean depth of 50X. We analyzed 32 Tumor/Normal pairs and 6 Tumor only Whole Genome Samples; 26 pts were classified as (R) and 12 as (NR). Raw sequencing data samples were aligned to hg38 genome build using Burrows-Wheeler Aligner (BWA) followed by duplicate-read removal and base-quality score recalibration using the Genome Analysis Toolkit (GATK). Somatic SNV and INDELS were called by combination of 5 callers (Mutect2, Strelka, VarScan, Platypus and SomaticSniper) for Tumor/Normal pairs and Mutect2 for Tumor only samples following the guidelines of GDC DNA-Seq analysis pipeline. Set of genes known to be significantly mutated in MIBC and shown to impact response/resistance to chemotherapy/immunotherapy respectively were selected. Samples were grouped by response status. Results: Median tumor mutational burden (TMB) for the dataset closely matches with TCGA results. Genes ERCC2, ARID1A, DSP, HMCN1, ERBB2, ERBB3, STAG2, BRCA2 present in (R) only, whereas VHL, ERCC4, PALB2, CDKN2A and CSMD3 present in (NR) only. We also grouped genes based on their biological processes by known Oncogenic Signaling Pathways and the 3 most common pathways are Genome Integrity, RTK Signaling and Transcription Factor with the latter two primarily enriched in (R). We identified a SNP rs2853669 in 5 (NR) and 14 (R). Conclusions: The genomic analysis suggests ERCC2, ARID1A, DSP, HMCN1, ERBB2, ERBB3,STAG2, BRCA2 correlated with PaR and VHL, ERCC4, PALB2, CDKN2A and CSMD3 correlated with lack of response. In addition, RTK Signaling and Transcription Factor were primarily enriched in (R). This genomic correlation of response/resistance to neoadjuvant chemo-immunotherapy in MIBC can help guide future biomarker-driven studies. Clinical trial information: NCT03294304 .

37 Background: Compared to the urban population, pts in rural areas face healthcare disparities and experience inferior healthcare-related outcomes. Herein we aimed to compare the health care quality metrics and outcomes between pts with aPC from rural versus urban areas treated at a tertiary cancer hospital. Methods: In this IRB approved retrospective study, eligibility criteria were: presence of aPC, treatment at a single center (NCI-Designated Comprehensive Cancer Center (NCI-CCC), between 10/2017 to 9/2021). Rural-urban commuting area (RUCA) codes from the 2010 census /were used to classify the pts’ residences as urban (1-3) or rural (4-10) areas. The straight-line to distance of the pts’ place of residence from our institute was also calculated and included in the analysis. The median household income data were obtained and calculated from “The Michigan Population Studies Center”, based on individual zip codes. Results: A total of 994 pts were eligible and included (83.9% urban vs 16.1% rural). The baseline demographic profile and tumor characteristics were similar between the two groups. The median household income of pts from urban areas was higher by $8604/annum than that from rural areas (p

PURPOSE In this phase II response-adaptive trial, we investigated the rational application of immune checkpoint blockade in renal cell carcinoma (RCC; ClinicalTrials.gov identifier: NCT03203473 ). METHODS We enrolled patients with metastatic RCC with no prior checkpoint inhibitor exposure. All patients received nivolumab alone with subsequent arm allocation based on response. Patients with a confirmed partial response (PR) or complete response (CR) within 6 months discontinued nivolumab and were observed (arm A). Patients with stable disease or progressive disease (PD) after no more than 6 months of nivolumab received two doses of ipilimumab (arm B). The primary endpoints were the proportion of patients with PR/CR at 1 year after nivolumab discontinuation (arm A) and proportion of nivolumab nonresponders who converted to PR/CR after ipilimumab (arm B). RESULTS Overall, 83 patients initiated treatment, of whom 96% had clear-cell histology, 51% were treatment naïve, and 67% had intermediate/poor-risk disease. Median follow-up was 19.5 months. Within 6 months, induction nivolumab resulted in a confirmed PR in 12% of patients (n = 10). Fourteen patients were not allocated to a study arm (seven because of toxicity, seven because of PD). Twelve patients (14%) were allocated to arm A and discontinued nivolumab, of whom five (42%; 90% CI, 18% to 68%) remained off nivolumab at ≥ 1 year. Of 57 patients (69%) allocated to arm B, two patients converted to a confirmed PR (4%; 90% CI, 1% to 11%), and no CRs were observed. CONCLUSION In this study, nivolumab followed by two doses of ipilimumab resulted in no CRs and a low PR/CR conversion. The number of patients evaluated for nivolumab discontinuation was too small to assess the value of this approach. Currently, our data do not support a response-adaptive strategy for checkpoint blockade in advanced RCC.

Background Genomic biomarkers that predict response to anti‐PD1 therapy in prostate cancer are needed. Frameshift mutations are predicted to generate more neoantigens than missense mutations; therefore, we hypothesized that the number or proportion of tumor frameshift mutations would correlate with response to anti‐PD1 therapy in prostate cancer. Methods To enrich for response to anti‐PD1 therapy, we assembled a multicenter cohort of 65 men with mismatch repair‐deficient (dMMR) prostate cancer. Patient characteristics and outcomes were determined by retrospective chart review. Clinical somatic DNA sequencing was used to determine tumor mutational burden (TMB), frameshift mutation burden, and frameshift mutation proportion (FSP), which were correlated to outcomes on anti‐PD1 treatment. We subsequently used data from a clinical trial of pembrolizumab in patients with nonprostatic dMMR cancers of various histologies as a biomarker validation cohort. Results Nineteen of 65 patients with dMMR metastatic castration‐resistant prostate cancer were treated with anti‐PD1 therapy. The PSA50 response rate was 65%, and the median progression‐free survival (PFS) was 24 (95% confidence interval 16–54) weeks. Tumor FSP, more than overall TMB, correlated most strongly with prolonged PFS and overall survival (OS) on anti‐PD1 treatment and with density of CD8+ tumor‐infiltrating lymphocytes. High FSP similarly identified patients with longer PFS as well as OS on anti‐PD1 therapy in a validation cohort. Conclusion Tumor FSP correlated with prolonged efficacy of anti‐PD1 treatment among patients with dMMR cancers and may represent a new biomarker of immune checkpoint inhibitor sensitivity. Implications for Practice Given the modest efficacy of immune checkpoint inhibition (ICI) in unselected patients with advanced prostate cancer, biomarkers of ICI sensitivity are needed. To facilitate biomarker discovery, a cohort of patients with DNA mismatch repair‐deficient (dMMR) prostate cancer was assembled, as these patients are enriched for responses to ICI. A high response rate to anti‐PD1 therapy in these patients was observed; however, these responses were not durable in most patients. Notably, tumor frameshift mutation proportion (FSP) was identified as a novel biomarker that was associated with prolonged response to anti‐PD1 therapy in this cohort. This finding was validated in a separate cohort of patients with nonprostatic dMMR cancers of various primary histologies. This works suggests that FSP predicts response to anti‐PD1 therapy in dMMR cancers, which should be validated prospectively in larger independent cohorts., Biomarkers of immune checkpoint inhibition sensitivity are needed. This article reports on genomic biomarkers that may predict response to anti‐PD1 therapy in prostate cancer.

Recently, mutations in speckle-type pox virus and zinc finger protein (SPOP) gene (mutant SPOP [mtSPOP]) have been associated with improved outcomes to abiraterone in the castration-resistant setting. We hypothesized that mtSPOP would be associated with improved outcomes to systemic therapy in men with de novo metastatic castration-sensitive prostate cancer (d-mCSPC). Retrospective data of newly diagnosed d-mCSPC patients were collected from four institutions. Eligibility criteria included standard androgen deprivation therapy without intensification, and SPOP mutational status (mtSPOP or wild-type SPOP [wtSPOP]) determination by targeted next-generation sequencing from tumor biopsies. A total of 121 men (25 mtSPOP [21%] and 96 wtSPOP [79%]) were included. After adjusting for covariates, mtSPOP was significantly associated with better median progression-free survival (35 vs 13 mo; adjusted hazard ratio [HR] 0.47; p = 0.016) and overall survival (97 vs 69 mo; adjusted HR 0.32; p = 0.027), with similar HR and p value on the univariate analysis. These findings, upon external validation, may assist with counseling and prognostication in the clinic, and inform the design of future clinical trials in this setting. Patient summary : Presence of tumor mutation in speckle-type pox virus and zinc finger protein (SPOP) gene was associated with improved survival outcomes in men with de novo metastatic castration-sensitive prostate cancer receiving standard androgen deprivation therapy.

PURPOSE In prostate cancer, inactivating CDK12 mutations lead to gene fusion–induced neoantigens and possibly sensitivity to immunotherapy. We aimed to clinically, pathologically, and molecularly characterize CDK12-aberrant prostate cancers. METHODS We conducted a retrospective multicenter study to identify patients with advanced prostate cancer who harbored somatic loss-of-function CDK12 mutations. We used descriptive statistics to characterize their clinical features and therapeutic outcomes (prostate-specific antigen [PSA] responses, progression-free survival [PFS]) to various systemic therapies, including sensitivity to poly (ADP-ribose) polymerase and PD-1 inhibitors. RESULTS Sixty men with at least monoallelic (51.7% biallelic) CDK12 alterations were identified across nine centers. Median age at diagnosis was 60.5 years; 71.7% and 28.3% were white and nonwhite, respectively; 93.3% had Gleason grade group 4-5; 15.4% had ductal/intraductal histology; 53.3% had metastases at diagnosis; and median PSA was 24.0 ng/mL. Of those who underwent primary androgen deprivation therapy for metastatic hormone-sensitive disease (n = 59), 79.7% had a PSA response, and median PFS was 12.3 months. Of those who received first-line abiraterone and enzalutamide for metastatic castration-resistant prostate cancer (mCRPC; n = 34), 41.2% had a PSA response, and median PFS was 5.3 months. Of those who received a first taxane chemotherapy for mCRPC (n = 22), 31.8% had a PSA response, and median PFS was 3.8 months. Eleven men received a PARP inhibitor (olaparib [n = 10], rucaparib [n = 1]), and none had a PSA response (median PFS, 3.6 months). Nine men received a PD-1 inhibitor as fourth- to sixth-line systemic therapy (pembrolizumab [n = 5], nivolumab [n = 4]); 33.3% had a PSA response, and median PFS was 5.4 months. CONCLUSION CDK12-altered prostate cancer is an aggressive subtype with poor outcomes to hormonal and taxane therapies as well as to PARP inhibitors. A proportion of these patients may respond favorably to PD-1 inhibitors, which implicates CDK12 deficiency in immunotherapy sensitivity.