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12039 Background: ICIs have changed the treatment paradigm in many cancer histologies. Population-level data regarding the impact of ICIs on the contemporary US cancer patients is scarce. In addition, elderly patients were underrepresented in the landmark trials. Methods: Metastatic cancers (melanoma, lung cancer, kidney cancer, head and neck cancer, Hodgkin’s lymphoma, and urothelial cancer) diagnosed between 2004-2018 were identified in the Surveillance, Epidemiology, and End Results (SEER) database. The year of the first FDA approved ICI in each cancer site was considered the commencement of the ICI era. The impact of metastatic cancers diagnosed in the ICI era was assessed in each age group (

e17053 Background: 18F-DCFPyL (piflufolastat F 18) is a PSMA-targeted agent FDA-approved for PET imaging in men with prostate cancer. Given the recent availability for clinical use, we sought to evaluate the impact and potential changes in management after the incorporation of 18F-DCFPyL (PyL) PET/CT at an academic medical center. Methods: We reviewed the first 100 PyL PET/CT scans performed at the Vanderbilt-Ingram Cancer Center for men with prostate adenocarcinoma. Patient demographics, treatment history, and prior imaging results were recorded, along with PyL PET results, most recent PSA, and clinical management plans. Management changes were designated as change in systemic therapy, radiation, or surgery and were determined by two independent reviewers with a third reviewer for any discordant cases. Results: There were 100 men included with PyL PET scans dating from 9/1/21 to 12/31/21. The median age was 69 years, 76% of patients were white and 13% were black. The median Gleason sum at diagnosis was 7 (4+3), 55% of men had prior prostatectomy, and 38% had prior radiation to the prostate/pelvis. The median PSA prior to PyL PET scan was 1.86 (IQR 0.53-9.95 ng/mL), 32% of men had previous ADT exposure, and 15% were on ADT at the time of PyL PET scan. The clinical setting prior to PyL PET scan was initial staging 22%, biochemical recurrence 59%, m1HSPC 14%, m0CRPC 2%, and m1CRPC 3%. There were 16 patients who had a prior 18F-fluciclovine within six months of PyL PET; of these 69% (11/16) had additional disease on PyL PET not previously identified. Activity in lymph nodes was observed in 48%, bone 37%, visceral sites 3%, prostate/prostate bed 46%, and 15% had no PSMA-avid disease. Clinical staging was altered after the PyL PET scan in 55% of patients, with the most common change being from BCR to m1HSPC (40/55). Clinical management was altered in 59% of cases: systemic therapy 38%, radiation planning 46%, and surgical planning 6% (Table). Conclusions: Clinical management was affected in 59% of cases after implementation of PyL PET in this retrospective, single center review. Given the rapid adoption of PSMA-targeted PET imaging agents, further studies are needed to evaluate the clinical impact of subsequent changes to management planning, as well as to develop multidisciplinary consensus statements and protocols to guide management.[Table: see text]

4541 Background: Immunotherapy (IO) has become the standard of care in patients with metastatic renal cell carcinoma (mRCC), yet clinical biomarkers of outcome remain elusive. Preclinical and clinical studies have demonstrated that a lower tumor volume burden is associated with better response to IO in melanoma and lung cancer. Methods: Retrospective chart review of mRCC patients treated with Immunotherapy/Immunotherapy or Immunotherapy/Tyrosine kinase inhibitors (TKI) combinations at Vanderbilt Ingram Cancer Center was conducted. Baseline target tumor lesions including primary kidney tumors and treatment response were assessed by RECIST 1.1 criteria. The association between baseline tumor burden and outcomes of interest [progression-free survival (PFS) and overall survival (OS)] were assessed with multivariable Cox regression model. Results: 79 patients with mRCC were included in the cohort. The median age was 64, 80% were male, 82% had clear cell histology, and 73% were IMDC intermediate/poor risk group. 53% received IO/IO and 39% received IO/TKI. 71% had prior nephrectomy and 14% had prior systemic therapy. The median baseline tumor burden was 87 mm (range: 16-363 mm). After adjusting for age, gender, histology, prior nephrectomy/systemic therapy and IMDC risk, baseline tumor burden was not associated with either PFS (p-value: 0.42) or OS (p-value: 0.99). At the initial follow-up scan (median time of 3.1 months from treatment initiation) 22 (28%) patients had an objective response and 41 (52%) patients had stable disease. Among patients with tumor shrinkage, every 10% decrease seen in the sum of the target lesions was associated with improved PFS (AHR: 0.77, 95%CI: 0.63-0.94, p-value:0.009) and OS (AHR: 0.62, 95%CI: 0.42-0.93, p-value:0.02). Conclusions: While baseline tumor burden volume was not associated with clinical outcome to immunotherapy-based therapy in patients with metastatic RCC; however, the degree of early tumor shrinkage was significantly associated with better outcomes. Large tumor burden does not preclude response and good outcome to immunotherapies.

4527 Background: Low baseline NER has been associated with improved response to immunotherapy in mRCC (PMID:34732251). The current study aimed to investigate the early decline of NER at week 6 after ipilimumab/nivolumab (ipi/nivo) initiation and treatment responses in mRCC. Methods: Retrospective chart review of ipi/nivo-treated mRCC patients at Vanderbilt-Ingram Cancer Center and Duke Cancer Institute was conducted. Landmark analysis at week 6 after ipi/nivo initiation was performed to assess the association between change in NER and clinical responses [progression-free survival (PFS)/overall survival (OS)]. Results: There were 150 mRCC patients included in the analysis: 78% had clear cell histology, 78% were IMDC intermediate/poor risk, and 74% were male. The median follow-up time was 11.9 months. After ipi/nivo initiation, the median NER decreased from 23.8 (interquartile range: 15.0-57.1) at baseline to 19.8 (10.6-40.8) at week 6; 102 (68%) patients had decreased NER. The NER at week 6 was grouped by percent change (≥ 50% decrease vs