Frequency and outcomes of molecularly guided off-label targeted agent prescriptions in the VA National Precision Oncology Program (NPOP).

e18676 Background: The increasing availability of comprehensive genomic profiling (CGP) and a growing number of targeted agents (TAs) has led to substantial improvements in outcomes among cancer pts with actionable mutations. CGP has led to identification of both on-label (level 1) variants, for which TAs have known efficacy, and off-label variants with lesser strength of supporting data. We sought to evaluate real-world prescription patterns and outcomes of off-label TA prescriptions among pts who underwent CGP. Methods: The NPOP database and VA Corporate Data Warehouse were queried to identify pts who had underwent CGP between February 2019 and December 2021 and were prescribed at least 1 of 73 TAs before January 2022. TAs prescribed for FDA-approved indications not relying on CGP as a companion diagnostic were excluded. OncoKB was used to annotate gene variants and evaluated against prescriptions to select pts who received off-label TAs. The frequency of off-label TA use, and for those treated > 4 weeks, rate of pts treated for 6 months or longer, median treatment duration and overall survival (OS) were computed. Results: Of the 18686 patients who underwent CGP, 2107 (11%) were prescribed any TA, and 191 (1%) were prescribed off-label TAs, with 31 receiving multiple concurrent or sequential off-label TAs. Mean age was 65.5 years, and 88% were male. TAs were most often prescribed for cancers of unknown primary (CUP, 29), NSCLC (24), and colorectal cancer (22). Frequency of off-label prescriptions was highest for pts who completed CGP for thyroid cancer (9%), breast cancer (8%), and CUP (2%). Most common variants involved BRAF (21%), ERBB2 (18%), BRCA1/BRCA2/ATM (9%), and PIK3CA (6%). Among all 164 pts treated > 4 weeks, 40% received TAs for 6 months or longer, including 50%, 47%, and 46% of pts bearing BRAF-, ERBB2-, and PIK3CA-mutant disease, respectively. Median therapy duration and OS was 141 [78.5 – 317, IQR] days and 181 [96.5 – 304.5, IQR] days, respectively. Conclusions: Though overall use of off-label TAs following CGP is low, nearly 10% of advanced thyroid and breast cancer patients are prescribed TAs for off-label indications. Forty percent of all pts receiving off-label TAs continue for at least 6 months, with higher rates for pts bearing BRAF-, ERBB2-, and PIK3CA-mutant disease. CGP-guided off-label treatment approaches offer unique options for advanced stage cancer with amenable molecular profiles.