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e16564 Background: Positron emission tomography with (18F)-fluorodeoxyglucose (FDG-PET) is not considered a standard of care (SOC) in renal cell carcinoma (RCC) because of its variability in metabolic activity. We investigated the rate of PET-positivity in our institutional cohort and tested whether PET-positivity had prognostic value in metastatic (m)RCC. Methods: Patients with FDG-PET imaging at any time during the course of disease were identified from medical records. PET-positivity was defined according to PERCIST criteria and a five-point rating scale analogue to Deauville Scoring was used to stratify PET-avidity. Tracer uptake of the hottest lesion was measured as SUVmax. Clinical parameters and PET-positivitywere correlated with overall survival (OS). Kaplan-Meier plots, log-rank analyses, kendall rank correlation, univariate and multivariable cox regression models were employed, where appropriate. Results: A totalof 90 patients was analyzed. The median age was 64.0 (34.0-83.0) and 56 (62.2%) patients had clear cell RCC. Metastatic disease was present in 64 (71.1%) and 22 (24.4%) patients received ongoing medical treatment. 72 (80.0%) patients had prior nephrectomy. PET-positivity occurred in 57 (63.3%) patients, with similar rates among metastatic (41/64; 64%) and non-metastatic patients (16/26; 62%). PET-positive patients had shorter median OS compared to PET-negative patients (38.5 months (CI95:24.5-NR) vs. not reached (CI95: 69.6-NR), P= 0.0013). A weak correlation was found between PET-Uptake and histologic grade (Kendall’s tau 0.22; P= 0.03). Prior nephrectomy, presence of primary lesions, presence of distant metastases, histologic grade and PET-positivity were significant predictors of OS in univariate regression. In multivariable analysis, only PET-positivity remained significant (HR 4.1 (CI95: 1.1-15.4), P= 0.04). Conclusions: RCC is a metabolically active cancer, which in the majority of patients is suitable for FDG-PET diagnostic procedures. PET-positivity was an independent prognostic factor for OS in RCC, indicating its putative clinical use. Further studies to define the role of FDG-PET imaging in RCC are ongoing.

217 Background: Neuroendocrine small cell prostate cancer (NEPC) is a lethal variant of prostate cancer (PCa) unresponsive to hormone therapy and associated with poor prognosis. Cisplatin induces short-lived responses and therefore alternative novel therapeutic options are urgently needed. Methods: Prostate specimens from radical prostatectomy or transurethral resection (benign prostate specimens n = 4, primary untreated or neoadjuvant hormone-treated adenocarcinoma n = 30, castrate-resistant prostate cancer-CRPC n = 38 and NEPC n = 16) were evaluated for PD-L1 (SpringBio, M4420), AR, chromogranin A, synaptophysin, NSE and CD56 expression by immunohistochemistry (IHC). Archival tissue from liver, lymph nodes and prostate from 30 additional patients with de novo and treatment emergent NEPC were analyzed for PD-L1 expression by IHC. The intensity was assessed as percentage of positive cells / mm2 of tissue. Targeted and whole exome sequencing of the high-density tumor areas were performed and correlated to the PD-L1 status (PD-L1+ve: > 1% of positive cells). OS was calculated from the date of diagnosis of NEPC to death. We set out to define PD-L1 expression and immunogenomic characteristics of NEPC. Results: PD-L1 was expressed in 0%, 5%, 10% and 41% of benign, adenocarcinoma, CRPC and NEPC specimens, respectively. The PD-L1 expression intensity was significantly higher in patients with NEPC (mean: 40%, range: 5-100%) compared to benign, adenocarcinoma and CRPC samples (mean: 0%, 2% and 8%, respectively, P < 0.0001). There was a higher prevalence of biallelic DNA Repair Defects (DRD) in the PD-L1+ve vs PD-L1-ve patients (65% vs 0%, P = 0.005). The median OS of the NEPC patients was 8.5 months vs 10.5 months in PD-L1+ve vs PD-L1-ve tumors (HR 1.24, 95% CI: 0.59-2.75, p = 0.55). Conclusions: NEPC have greater PD-L1 expression than adenoCa and CRPC. Biallelic DRD was exclusively observed in PD-L1+ve patients. Since PD-L1 expression and DRD have been associated to response to PARP and PD1/PD-L1 inhibitors in prostate and other cancers, further studies evaluating the activity of those agents in NEPC patients are warranted.