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PURPOSE Compared with people living without HIV (PWOH), people living with HIV (PWH) and cancer have traditionally been excluded from immune checkpoint inhibitor (ICI) trials. Furthermore, there is a paucity of real-world data on the use of ICIs in PWH and cancer. METHODS This retrospective study included PWH treated with anti–PD-1- or anti–PD-L1-based therapies for advanced cancers. Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). Objective response rates (ORRs) were measured per RECIST 1.1 or other tumor-specific criteria, whenever feasible. Restricted mean survival time (RMST) was used to compare OS and PFS between matched PWH and PWOH with metastatic NSCLC (mNSCLC). RESULTS Among 390 PWH, median age was 58 years, 85% (n = 331) were males, 36% (n = 138) were Black; 70% (n = 274) received anti–PD-1/anti–PD-L1 monotherapy. Most common cancers were NSCLC (28%, n = 111), hepatocellular carcinoma ([HCC]; 11%, n = 44), and head and neck squamous cell carcinoma (HNSCC; 10%, n = 39). Seventy percent (152/216) had CD4+ T cell counts ≥200 cells/µL, and 94% (179/190) had HIV viral load CONCLUSION Among PWH, ICIs demonstrated differential activity across cancer types with no excess toxicity. Safety and activity of ICIs were similar between matched cohorts of PWH and PWOH with mNSCLC.

8574 Background: Small-cell lung cancer (SCLC) is a highly aggressive neuroendocrine lung cancer, accounting for 10-15% of all lung cancers, commonly classified in limited stage (LS-SCLC) and extensive stage (ES-SCLC). Despite the introduction of chemoimmunotherapy as new standard first-line therapy for ES-SCLC, the benefit of addition of the programmed-death ligand 1 (PD-L1) inhibitors is limited to a subset of patients, suggesting the importance to identify predictive biomarkers of response. [18F]FDG-PET/CT is commonly used for the staging and therapeutic planning of SCLC patients. Metabolic parameters derived from [18F]FDG-PET could predict patient outcomes by measuring the extension of metabolically active tumor (metabolic tumor volume [MTV]) or its metabolic heterogeneity (total lesion glycolysis [TLG]). Methods: We retrospectively collected patients with pathologically confirmed diagnosis of SCLC, who had undergone an [18F]FDG PET/CT scan within 30 days from the start of first-line treatment for ES-SCLC. Patients with LS-SCLC at diagnosis were included if presenting relapse at pre-treatment scans performed at least 90 days from the end of treatment with radical intent. We calculated metabolic parameters, MTV and TLG, by summing each single lesion’s MTV and TLD respectively. The primary endpoint of the study was overall survival (OS), defined as the time from [18F]FDG PET/CT scan acquisition to death from any cause. Results: A total of 86 SCLC patients ES-SCLC were included. Patients with hyponatremia, hypoalbuminemia and elevated LDH levels were associated with greater number of lesions, greater total MTV, and higher total TLG at [18F]FDG-PET/CT/CT scan. At a median follow-up of 20.9 months, the median OS was 11.1 months. Median survival was longer among patients with Na + ≥135 mEq/L, with normal albumin levels and in those with normal LDH levels and without bone metastases. Patients with low total MTV had longer OS compared with those with high total MTV (11.9 months vs 4.8 months, respectively). High total MTV was independently associated with the risk of death (p < 0.001) but not with the risk of progression. Conclusions: Our preliminary data showed that total MTV could provide prognostic information in patients with ES-SCLC, suggesting a potential role as stratification factor in immunotherapy-based clinical trials.

9021 Background: Despite improvements in survival with immune checkpoint inhibition (ICI), the majority of patients develop acquired resistance to ICI after an initial benefit. However, the mechanisms underlying acquired resistance to ICI in NSCLC are largely unknown. Methods: Patients with advanced NSCLC treated with ICI at the Dana-Farber Cancer Institute (DFCI), and whose tumors underwent genomic profiling before and after ICI, with no intervening therapies, were included. Mutations, tumor mutational burden (TMB), copy number variations (CNVs), and PD-L1 tumor proportion score (TPS) were compared between pre- and post-ICI samples. Acquired resistance was defined as the development of disease progression after an initial objective response, or stable disease ≥3 months with PD-(L)1 blockade. Results: Among 1763 patients with advanced NSCLC who received ICI, 45 had matched pre- and post-ICI tissue samples available for genomic profiling. Putative mechanisms of resistance were identified in 55% of cases (N = 25). Five patients (20%) acquired an STK11 mutation, one patient (4%) acquired a KEAP1 mutation, and another patient (4%) developed concurrent KEAP1 and SMARCA4 mutations. A patient (4%) with KRAS G12C-mutant NSCLC developed concurrent STK11 and KEAP1 mutations at resistance. In 3 cases (12%) with pre-existing STK11 or KEAP1 mutations prior to ICI administration, we identified acquired copy losses of STK11 and KEAP1, respectively, resulting in bi-allelic inactivation of these genes. Acquired beta-2-microglobulin ( B2M) mutations were detected in 3 patients (12%), one of whom developed concurrent B2M copy loss, indicating bi-allelic inactivation. Eight additional patients (32%) developed B2M gene deletions. Other acquired alterations that have been implicated in ICI resistance included CDKN2A/B loss (N = 10, 40%), including 5 with bi-allelic deletion, acquired PTEN deletions (N = 5, 20%), and MDM2 amplification (N = 2, 8%). When we examined alterations in immune checkpoint genes, we identified acquired CD274 (PD-L1) and PDCD1LG2 (PD-L2) loss in 8% of cases (N = 2), and bi-allelic deletion in one case (4%). Intervening ICI did not affect TMB (median TMB: 8.7 [pre-ICI] vs 9.1 [post-ICI] mut/Mb, P = 0.6), PD-L1 expression (median PD-L1 TPS: 3% [pre-ICI] vs 5.0% [post-ICI] mut/Mb, P = 0.5), or aneuploidy levels (as fraction of genome altered [FGA]) (median FGA: 18.4% [pre-ICI] vs 21.1% [post-ICI], P = 0.2), indicating that acquired gene level CNVs were not a reflection of increased cancer aneuploidy. In a control cohort of 30 patients with pre- and post-chemotherapy matched samples which underwent genomic profiling, no acquired mutations in STK11, KEAP1, SMARCA4, or B2M were detected. Conclusions: Mechanisms of acquired resistance to PD-(L)1 blockade are heterogenous, and new therapeutic strategies are required to delay and overcome ICI resistance in patients with NSCLC.

8514 Background: Compared to lung adenocarcinomas (LUAD) with nonsolid-predominant histology (lepidic, acinar, papillary, micropapillary), those with predominantly solid features have a higher risk of disease recurrence after surgical resection. However, little is known about the genomic landscape and immunophenotype of solid vs nonsolid stage I LUAD. Methods: We collected clinicopathologic data from patients with resected stage I NSCLC (AJCC 8th Edition), which underwent next-generation sequencing to identify genomic alterations and tumor mutational burden (TMB). A subset of these samples also had multiplexed immunofluorescence for CD8+, FOXP3+, PD-1+, and PD-L1 to determine differences in tumor immune cells subsets according to histologic subtype. Disease free-survival (DFS) was compared in patients based on their predominant histologic subtype (solid vs nonsolid). Results: Among 658 LUADs, 11.4% (N = 75) had solid-predominant and 88.6% (N = 583) nonsolid-predominant histology. After a median follow-up of 50 months from the time of surgery, 145 patients (22.0%) experienced recurrence. Compared to nonsolid-predominant LUAD, those with solid predominance had a significantly lower prevalence of activating EGFR, BRAFV600E, and METex14 mutations as well as ALK/ RET/ ROS1 rearrangements (9.3% versus 31.6%, P < 0.001), no difference in KRASG12C frequency (24% versus 16.8%, P = 0.14), a higher TMB (median 12.2 versus 7.2 mutations/megabase; P < 0.001), and a shorter median DFS from the time of surgical resection (43.2 months versus not reached, HR: 3.3 [95% CI: 2.2-4.9], P < 0.001). The detrimental effect of solid-predominant LUAD in DFS remained significant after adjusting for other factors such as tumor stage, surgery type, smoking status, and TMB (HR: 2.66 [95% CI: 1.71-4.11], P < 0.001]. Among LUADs profiled by multiplex immunofluorescence, compared to tumors with nonsolid-predominant subtype (N = 197), those with solid predominance (N = 23) had significantly higher numbers of CD8+, FOXP3+, PD-1+ immune cells, and PD-1+ CD8+ T cells, both intratumorally (P < 0.001) and at the tumor-stroma interface (P < 0.001). Solid-predominant subtype was also associated with a higher median PD-L1 expression level on tumor (5% versus 1%; P = 0.01) and immune cells (16% versus 7%, P = 0.02). Conclusions: Among patients with surgically-resected stage I LUAD, solid-predominant histology was associated with distinct genotypic and immunologic characteristics. These findings may aid in identifying patients at greater risk of recurrence after surgery.

9054 Background: Older age is associated with increased levels of systemic inflammation and altered immunosurveillance in cancer. Whether aging correlates with a distinct immunophenotype or impacts clinical outcomes to first-line pembrolizumab in patients with advanced non-small-cell lung cancer (NSCLC) and a PD-L1 tumor proportion score (TPS) of ≥50% is unclear. Methods: We performed a retrospective analysis of patients with NSCLC. Multiplexed immunofluorescence (mIF) for CD8+, PD-1+, PD-1+CD8+ and FOXP3+ was performed to explore tumor immunophenotype. Clinical outcomes were analyzed on a separate cohort of patients with PD-L1-high (TPS of ≥50%) NSCLC (negative for sensitizing genomic alterations in EGFR and ALK) who received treatment with first-line pembrolizumab. Variables demonstrating a univariate signal of association of p < 0.1 were included in the multivariate model. The results were compared in patients < 80 vs ≥80 years old. Results: Among 541 patients with NSCLCs profiled by mIF, the median age was 67 (28-90). When comparing patients < 80y (n = 497) to ≥80y (n = 44), there was no difference in median CD8+ T cells/mm2 (171 vs 148; p = 0.69), PD-1+ immune cells/mm2 (81.1 vs 87.2; p = 0.95), or PD-1+CD8+ T cells/mm2 (18.0 vs 13.1; p = 0.56). NSCLCs from patients ≥80y had a higher median of intratumoral-associated FOXP3+ T cells/mm2 (63.6 vs 91.1; p = 0.03). In a cohort of 271 patients with PD-L1 ≥50% who received first-line pembrolizumab, baseline clinicopathological characteristics were balanced in the < 80y (n = 225) vs ≥80y (n = 46) groups in terms of sex, tobacco use, Eastern Cooperative Oncology Group-Performance Status (ECOG-PS), histology, presence of potentially targetable driver mutations (KRAS, MET, BRAF, HER2, RET), and PD-L1 TPS distribution (50-89% vs ≥90%). Compared to patients < 80y, patients ≥80y had no difference in objective response rate (ORR 39.1% vs 28.2%; p = 0.22) or median progression-free survival (mPFS 6.0 vs 3.0 months; p = 0.16). However, patients ≥80y had a shorter median overall survival (mOS 25.7 vs 7.6 months; p = 0.02), and this result remained significant after adjusting for ECOG-PS. Among those who experienced disease progression on pembrolizumab, patients ≥80y were significantly less likely to receive any second-line systemic therapy compared to patients < 80y (55.6% vs 30.8%; p = 0.008). Conclusions: In patients with NSCLC and PD-L1 ≥50%, the ORR and mPFS to first-line pembrolizumab were similar between patients < vs ≥80 years old. OS was shorter among patients ≥80y, potentially reflecting lower use of second-line therapy in elderly patients after progression on pembrolizumab. The immunophenotypic correlates of NSCLC in older patients need further investigation.

9043 Background: Although 1st-line PD-1 monotherapy has improved survival in advanced NSCLC with a PD-L1 TPS ≥50%, responses occur in ̃45% of patients (pts). We previously showed that among pts treated with 1st-line pembrolizumab, clinical outcomes were significantly improved in those with a PD-L1 TPS of ≥90% compared to a TPS of 50-89%. Here, we report the 3-year survival analysis to 1st-line pembrolizumab in pts with a PD-L1 TPS ≥90% vs 50-89%, and characterize genomic and immunophenotypic differences between these PD-L1 expression groups. Methods: Pts with stage IV EGFR/ALK wild-type NSCLC and PD-L1 TPS ≥50% who received 1st-line pembrolizumab at the Dana-Farber Cancer Institute (DFCI) and Memorial Sloan Kettering Cancer Center (MSKCC), with a minimum follow-up of 3 years were included. Comprehensive tumor genomic profiling and multiplexed immunofluorescence (mIF) were performed to examine genomic and immunophenotypic correlates of very high PD-L1 expression on separate cohorts of NSCLC at the DFCI. Results: Among 396 pts, median age was 69, 53.3% were women, 90.1% had a history of tobacco use, 83.6% had a ECOG performance status of 0-1, and 28.8% had a KRAS mutation. At a median follow-up of 42.6 months, median progression-free (mPFS) and overall survival (mOS) in the entire cohort were 5.1 months, and 19.0 months, respectively. When compared to pts with a PD-L1 TPS of 50-89% (N = 252), those with PD-L1 TPS ≥90% (N = 144) had a significantly longer mPFS (6.0 vs 4.5 months, HR 0.67, p < 0.001), and longer mOS (30.2 vs 16.9 months, HR 0.66, p < 0.01). Kaplan-Meier estimates of the 3-year PFS and OS were 24.9% and 47.0% in the PD-L1 TPS ≥90% groups, and 9.4% and 27.7% in the PD-L1 TPS 50-89% group, respectively. A PD-L1 TPS ≥90% was confirmed to be an independent predictor of improved PFS (HR 0.68, p < 0.01) and OS (HR 0.67, p < 0.01) in multivariable analysis. Tumor genomic profiling from a separate cohort of 500 NSCLC samples revealed that mutations in STK11, KEAP1, FBXW7, and CTNNB1 were significantly more frequent in tumors with a PD-L1 TPS of 50-89% compared to those with a PD-L1 TPS ≥90% (q < 0.05). mIF on 91 NSCLCs identified significantly higher CD8+PD1+ T cells and PD-L1+ immune cells in tumors with PD-L1 TPS ≥90% vs 50-89% (p < 0.05). Conclusions: Pembrolizumab monotherapy continues to demonstrate a meaningful long-term survival benefit in pts with advanced NSCLC and a PD-L1 TPS ≥90%. NSCLCs with very high PD-L1 TPS may have a more favorable genomic and immunophenotypic profile. These findings have implications for treatment selection and clinical trial interpretation and design.

9124 Background: In non-small cell lung cancer (NSCLC), MET exon 14 skipping (METex14) mutations and MET amplification can be targeted with MET inhibitors. Here, we describe a novel, actionable molecular subtype of NSCLC characterized by activating MET-tyrosine kinase domain (MET-TKD) mutations in the absence of METex14 mutations. Methods: Clinicopathologic and genomic data were abstracted from NSCLC cases included in a multi-institutional cohort of tumors that underwent genomic profiling in the GENIE v10, China PanCancer, and the International Cancer Genome Consortium/ The Cancer Genome Atlas (ICGC/TCGA) datasets. External validation of the prevalence of MET-TKD mutations was performed on an independent cohort of NSCLC tissue and liquid samples from the Foundation Medicine genomic database. Results: Among 14,099 NSCLC samples in the multi-institutional cohort, 71 (0.5%) harbored MET-TKD mutations without concurrent METex14 mutations: 55 of these had uncertain pathogenic significance and 16 had known oncogenic potential, including MET H1094Y/R, D1228H/N/V, N1100S, H1106D, V1188I, and M1250T, in order of decreasing prevalence. In a separate cohort of 91,515 NSCLC samples from the Foundation Medicine database, MET-TKD mutations lacking concurrent METex14 mutations were identified in 799 (0.9%) samples, including H1094Y, L1195V, D1228H/N, M1250T and others. Among 60 NSCLC samples harboring MET-TKD mutations without concurrent METex14 mutations with complete genomic data in the multi-institutional cohort, 36 (60%) had concurrent driver alterations in KRAS, EGFR, ROS1, BRAF, HER2, or RET, while 24 (40%) had no concurrent oncogenic drivers. Among patients with available demographic data in the multi-institutional cohort, those with MET-TKD-mutant NSCLC (N = 70) were significantly younger than patients with METex14-mutant NSCLC (N = 353) (median age 63 [range 30-86] vs 73 [range 44-88], p < 0.0001), and there was no significant difference in sex or self-reported race. Confirmed partial responses to the MET tyrosine kinase inhibitor elzovantinib (TPX-0022) were observed in two patients with MET-TKD-mutant NSCLC and no other detectable driver mutations: a 64-year-old man with MET H1094Y-mutant NSCLC, and an 80-year-old man with MET F1200I-mutant NSCLC. Conclusions: Potentially actionable MET-TKD mutations lacking concurrent METex14 mutations represent a novel genomic subtype in 0.5-0.9% of NSCLC, and occur in the absence of other known drivers in a subset of cases.

e20515 Background: Large cell neuroendocrine carcinoma of the lung (LCNEC) is a rare tumor, with clinical and molecular features between non-small cell and small-cell lung cancer (NSCLC and SCLC, respectively). To date, little is known about factors able to predict clinical outcome of these patients. We sought to identify prognostic factors in LCNEC. Methods: We retrospectively collected pathologically-confirmed LCNEC patients treated at the S. Orsola Malpighi Hospital of Bologna between 01/01/2009 and 31/12/2020. LCNEC was defined as tumor with neuroendocrine morphology, expression of ≥2 neuroendocrine markers (including chromogranin A, synaptophysin, or CD56) at immunohistochemistry and high tumor grade (defined as necrosis and high Ki67 ≥ 50% or high mitotic rate, ≥ 10 mitoses per 2 mm2). Clinical features, pathological features, and blood test values (including neuron-specific enolase [NSE], carcinoembryonic antigen [CEA], cytokeratin 19 fragment [cyfra 21-1]) were correlated with progression-free survival to first-line chemotherapy (PFS) and overall survival from the diagnosis of extensive disease (OS). Results: Eighty-one LCNEC patients (median age 69 years, range 63-76) were identified. Twenty-seven (33.3%) had limited-stage disease and 52 patients (67.5%) had Eastern cooperative oncology group performance status (ECOG PS) ≥ 1 at diagnosis. When extensive disease was found (ED-LCNEC, N = 67), 23 patients (34.3%) had liver metastases, 10 (14.9%) had brain metastases and 24 (35.8%) had bone metastases. Treatment in ED-LCNEC was platinum plus etoposide in 45 patients (81.9%) and platinum plus paclitaxel in 10 patients (18.1%). Among 55 patients treated with platinum-based chemotherapy, 5 patients (9.1%) received cisplatin, while 50 (90.9%) received carboplatin. Overall, OS was 9.17 months (95% confidence interval [95%CI]7.17-13.87), PFS was 4.87 months (95%CI 4.21-6.02) and ORR was 38.2% (95%CI 25.4-42.3, N = 21/56). At univariate analysis, ECOG PS ≥ 1 (P = 0.049), presence of liver (P = 0.004) and bone metastases (P = 0.009), ≥ 2 non-nodal metastatic sites (P < 0.001), elevated NSE (P = 0.009) and CEA level at diagnosis (P = 0.011) were associated with increased risk of death. At multivariate analysis, ECOG PS ≥ 1 (P = 0.020), ≥ 2 metastatic sites (P = 0.002), and elevated NSE level at diagnosis (P = 0.009) were independently associated with the risk of death. At univariate analysis brain metastases (P = 0.017), ≥2 metastatic sites (P = 0.006) and elevated value of CEA at baseline (P = 0.026) were associated with increased risk of progression. At multivariate analysis, only the presence of brain metastases (P = 0.043) retained its association with the risk of progression. Conclusions: In ED-LCNEC of the lung, ECOG PS, number of non-nodal sites of metastases and NSE at baseline are associated with worse survival, while the presence of brain metastases is associated with shorter PFS.

9119 Background: Cancer aneuploidy, an unbalanced number of chromosomes, is associated with somatic mutation rate, expression of proliferative genes, and altered immune signaling. Whether aneuploidy correlates to a distinct immunophenotype or impacts clinical outcomes to immune checkpoint inhibitors (ICIs) in NSCLC is unclear. Methods: In NSCLCs which underwent targeted next-generation sequencing, we retrospectively analyzed the aneuploidy score (AS), defined as the sum of the number of altered chromosome arms. An unbiased recursive partitioning (URP) algorithm was used to investigate an AS cutoff to discriminate responders from non-responders to ICIs. Multiplexed immunofluorescence to quantify CD8+, Foxp3+, PD-1+, and PD-L1 expression was performed to determine differences in tumor immune cells subsets according to AS cutoff. Results: Among 436 NSCLCs identified, stage I tumors (median AS 1) had significantly lower median AS (mAS) than stage IV cancers (mAS 7, P < 0.001), stage III (mAS 4, P = 0.03), and numerically lower compared to stage II cancers (mAS 3, P = 0.18). We found no difference in the mAS across tumors with a PD-L1 tumor proportion score of ≥50%, 1-49%, or < 1% (mAS 5 vs 7 vs 6, respectively, P = 0.26), nor was there any correlation between aneuploidy and TMB when taken as continuous variables (Spearman R: 0.074, P = 0.12). A total of 279 advanced NSCLCs with available aneuploidy scores were treated with ICIs. An URP analysis identified an AS of 2 as the strongest discriminator of objective response to ICI. Compared to pts with an AS > 2 (N = 207, 74.2%), pts with AS ≤2 (N = 72, 25.8%) had a significantly higher objective response rate (ORR 43.0% vs 19.8%, P < 0.001), a significantly longer median progression-free survival (mPFS 6.2 vs 2.9 months, HR: 0.70 [95% CI: 0.52-0.94], P = 0.02), and a significantly longer median overall survival (mOS 19.8 vs 13.8 months, HR: 0.66 [95% CI: 0.47-0.94], P = 0.02) to treatment with ICIs. After adjusting for other variables such as performance status, presence of oncogenic driver mutation, PD-L1, TMB, and line of treatment, AS was significantly associated with improved mPFS (HR: 0.72 [95% CI: 0.52-0.99], P = 0.04) and mOS (HR: 0.64 [95% CI: 0.44-0.94], P = 0.02). By contrast, among pts who received first-line platinum doublet chemotherapy without ICI, an AS ≤2 (N = 29), when compared to an AS > 2 (N = 56), did not correlate with improved ORR (55.2% vs 44.6%, P = 0.4) or PFS (5.3 vs 4.8 months, HR 0.83 [95% CI: 0.5-1.3], P = 0.43). Among 179 NSCLCs profiled by multiplex immunofluorescence, compared to cancers with an AS > 2, those with low aneuploidy had significantly higher numbers of CD8+, Foxp3+, PD-1+ immune cells, and PD-1+ CD8+ T cell, both intratumorally and when looking at the total numbers of cells within the tumor and at the tumor-stroma interface. Conclusions: NSCLCs with low aneuploidy have a distinct immune microenvironment and more favorable outcomes to ICIs.

e16203 Background: Goblet cell carcinoma (GCC) is a rare mixed endocrine-neuroendocrine tumor arising almost exclusively in the appendix. The optimal management of these patients is still unclear, given GCC rarity and the difficulty in proper pathology diagnosis. We sought to explore the efficacy of adjuvant chemotherapy (ACT) in GCC extracted from the Surveillance, Epidemiology and End Result (SEER) US registry. Methods: Patients with pathology diagnosis of GCC were identified in the SEER registry by the 8243 ICD-09 code. Data about sex, age, tumor stage at diagnosis, number of analyzed and positive lymph-nodes, chemotherapy and survival were collected. Lymph node ratio (LNR) was calculated as the ratio between the number of metastatic lymph-nodes and removed lymph nodes. The best cutoff to predict survival state at 5-year from diagnosis was calculated. The primary endpoint was overall survival (OS). Results: Overall, 1055 GCC patients (51.7% male, median age 57 years) were identified. The median tumor diameter was 20 mm. According to the American Joint Committee on Cancer staging manual 7th edition, 128 patients (12.1%) had nodal involvement (N+): 95 were N1 and 33 were N2, while 66 (6.3%) had distant metastasis (M+). Prognostic LNR cutoff was 0.16. Using this cutoff, LNR was ≤0.16 in 674 patients (63.9%), and > 0.16 in 125 patients (11.8%). The median OS was 232 months (95% confidence interval [95%CI]: 153.4-310.5). Overall, 5-year survival rate (OS-5) was 73.4% (N = 453). At univariate analysis age, tumor diameter, M+, N+, number of lymph nodes removed, number of metastatic lymph nodes and LNR were significantly associated with the risk of death. At multivariate analysis, age, M+, N+, number of removed lymph nodes, and number of metastatic lymph nodes retained their association. After excluding M+ and N+ patients, 897 localized GCC patients (52.8% male) were analyzed. Fifty-five patients (6.1%) received ACT and OS-5 was 83.8% (N = 425). CT was administered more often in tumors with higher histological grade, higher T stage and greater tumor diameter. At the multivariate analysis, only age and number of removed lymph nodes were independently associated with the risk of death. Notably, ACT was not associated with increased survival. Ninety-two patients (57.6% male) had nodal involvement without distant metastases: 73 were N1 and 19 were N2. In 56 patients (60.9%) LNR was ≤0.16, while it was > 0.16 in 35 (38.0%). Thirty-five patients (38%) received ACT, without significant imbalances. OS-5 was 45.2% (N = 28). At univariate analysis, age, N2, number of metastatic lymph nodes and LNR were significantly associated with the risk of death. At multivariate analysis, only the number of metastatic lymph nodes retained its association. Of note, ACT was not associated with increased survival. Conclusions: In GCC, ACT was not associated with increased survival in our population-based analysis, irrespective of nodal involvement.

e16709 Background: The 2019 World Health Organization (WHO) classification of neuroendocrine neoplasia (NEN) introduced the new category of well-differentiated NEN with Ki67 proliferation index ≥20% (NET G3). Fluoropyrimidine-based regimens with oxaliplatin (FOLFOX/XELOX) were a treatment option in neuroendocrine carcinomas with low Ki67. However, FOLFOX/XELOX efficacy in this newly defined NET G3 category is unknown. Objective of this study was to describe FOLFOX/XELOX efficacy in NET G3 and identify factors associated with outcome. Methods: We retrospectively collected all metastatic gastro-entero-pancreatic NET G3 patients who received a fluoropyrimidine-based regimen with oxaliplatin (FOLFOX/XELOX) as first-line treatment at 4 NEN-dedicated Italian Centers. Concomitant somatostatin analog (SSA) treatment was allowed and recorded. Objective response rate (ORR) was defined according to RECIST criteria v1.1. Factors associated with progression-free survival (PFS), overall survival (OS), and ORR were analyzed. Results: Twenty-nine NET G3 patients (median age 57 years, range 18-79) matching inclusion criteria were identified. Twenty patients (69%) were of pancreatic origin, while 9 (31%) had gastrointestinal primary. Median Ki67 was 30% (range 21-50). Treatment was FOLFOX in 14 (48%) and XELOX in 15 patients (52%), while 12 (44%) received also concomitant SSA. After a median follow-up of 44.1 months, median PFS was 7.9 months (95%CI 6.2 -11.4) and median OS was 44.8 months (95%CI 37.1 - NA). The 12 patients whose tumor responded to treatment (44% [95%CI 26-65]) had longer PFS (26.5 vs 5.0 months; p = 0.004) and OS (194.0 vs 38.0 months; p = 0.04) compared to those who did not respond. Progressive disease was the best disease response in 7 patients (24%). Objective response was associated with a reduced risk for progression (HR: 0.22 [95%CI: 0.07-0.62]; p = 0.007) while higher Ki67 was associated with an increased risk for progression (HR: 1.11 [95%CI: 1.04-1.19]; p = 0.002) and for death (HR: 1.09 [95%CI: 1.01-1.17]; p = 0.017). After correcting for confounding factor, ORR (HR: 0.26 [95%CI: 0.08-0.83]; p = 0.023) and Ki67 (HR: 1.09 [95%CI: 1.02-1.16]; p = 0.009) retained their association with the risk for progression, but not with the risk for death. Conclusions: Fluoropyrimidine-based regimens with oxaliplatin (FOLFOX/XELOX) may be active and effective in NET G3 of gastroenteropancreatic origin.

2037 Background: Medulloblastoma is extremely rare in adults and, therefore, it is difficult to accrual patients in clinical trials. Radical surgery and radiotherapy (RT) provide a significant control of disease. Nevertheless, about 25% of average-risk patients have a relapse and die because of disease progression. The role of chemotherapy (CT) after standard RT for average-risk adult patients remains controversial. Methods: We analyzed 48 average-risk patients according to Chang classification diagnosed from 1988 to 2016. Median age was 29 years (range 16-61), M/F ratio was 26 (54.2%)/22 (45.8%). Fifteen patients had classic medulloblastoma (31.3%), 15 patients had desmoplastic medulloblastoma (31.3%), 5 patients had extensive nodularity (10.4%) and 2 patients had large cells/anaplastic histology (4.2%). The patients were homogeneously distributed in the two groups: 24 (50%) received adjuvant RT alone and 24 (50%) received RT + CT that consisted in a platinum-etoposide based combination. Results: After a median follow-up of 12.5 years, CT increases progression-free survival rate at 15 years (PFS-15 82.3 ± 8.0% in RT-CT group vs. 38.5% ± 13.0% in RT group p = 0.05) and overall survival rate at 15 years (OS-15 89.3% 7.2% vs. 52.0% 13.1%, p = 0.02). Among patients receiving CT, the reported grade ≥ 3 adverse events were: 9 cases of neutropenia; 6 cases of G3 neutropenia (25%) and 3 cases of G4 neutropenia (13%), 1 case of G3 thrombocytopenia (4%) and 2 cases of G3 nausea (8%). Conclusions: Our study with a long follow up period suggests that adding adjuvant chemotherapy to RT might improve PFS and OS in average-risk adult medulloblastoma patients.

2036 Background: The 2016 WHO classification dramatically changed the diagnosis of gliomas. Diffuse gliomas are classified according to the presence of IDH-mutation (IDH-mut) and the deletion of both 1p and 19q chromosome arms (1p/19q codel). Now debate is whether grade still has an independent prognostic value. The aim of this study was to find out if grade is a prognostic factor independently of molecular status. Methods: We analyzed our institutional data warehouse for all consecutive patients (pts) with newly diagnosed, histologically proven Grade II or Grade III IDH-mut gliomas. IDH 1/2 assessment by polymerase chain reaction (PCR)or immunohistochemistry (IHC) was accepted. Next Generation Sequencing (NGS) for IDH1(exon 4) and IDH2(exon 4) was performed on all specimens wild-type for the IDH. Results: The analysis included all the 399 pts who had a grade II (n = 250, 62.7%) or grade III (n = 149, 37.3%). Median follow-up time was 105.3 months. After surgery, 72 pts (18.0%) received RT alone, 44 (11.0%) received CT alone, 135 (33.8%) received both RT and CT, and 142 (35.6%) follow-up without any treatment. Median survival was 148.1 months. In multivariate analysis Grade (HR = 0.342, 95%CI: 0.221 – 0.531; P < 0.001) and 1p/19q codeletion (HR = 0.440, 95%CI: 0.290 – 0.668; P < 0.001) were independently associated with a lower risk for death. The difference in survival remained when adjusted for histological subtype. Residual disease after surgery or biopsy negatively affected survival (HR 2.151, 95%CI 1.375 – 3.367, P = 0.001). Post-surgical treatment with RT + adjuvant CT improves survival in respect to follow-up and other treatments (HR: 0.316, 95%CI 0.156 – 0.641, P = 0.001). Conclusions: Grade still affects survival in IDH mutant Grade II and III gliomas. This effect was independent onmolecular features, surgical extension and post-surgical treatments. Clinical management of gliomas should continue to take into account grade as well as molecular characteristics.

e14057Background: About 21-62% of GBM patients (pts) access to 3rd line therapy. In this setting, there is no defined standard. In this study we evaluated the outcome of pts who received 3rd line t...