Pembrolizumab (P) in patients (Pts) with colorectal cancer (CRC) with high tumor mutational burden (HTMB): Results from the Targeted Agent and Profiling Utilization Registry (TAPUR) Study.

133 Background: TAPUR is a phase II basket study evaluating anti-tumor activity of commercially available targeted agents in pts with advanced cancers with genomic alterations. Results in a cohort of CRC pts with HTMB treated with P are reported. Methods: Eligible pts had advanced CRC, no standard treatment (tx) options, measurable disease, ECOG PS 0-1, and adequate organ function. Genomic testing was performed in CLIA-certified, CAP-accredited site selected labs. Pts had HTMB, defined as ≥9 mutations/megabase (Muts/Mb) by a FoundationOne test (n=26) or other tests (n=2) approved by the Molecular Tumor Board. Pts with MSI-H tumors were ineligible. Dosing of P was 2 mg/kg (n=8) or 200 mg (n=20) IV over 30 mins, every 3 wks. Simon two-stage design was used to test a null rate of 15% vs. 35% (power = 0.85; α = 0.10). If ≥2 of 10 pts in stage 1 have disease control (DC) (objective response (OR) or stable disease at 16+ wks according to RECIST (SD16+)), 18 more pts enrolled. If ≥7 of 28 pts have DC, the tx is worthy of further study. Secondary endpoints are progression-free survival (PFS), overall survival (OS) and safety. Results: Twenty-eight pts enrolled from June 2017 to November 2018; 1 pt was ineligible and excluded. HTMB ranged from 9 to 54 Muts/Mb. Table (N=27) summarizes demographics and outcomes. Tumor MS status was reported stable for 25 pts, ambiguous for 1 pt, and not available for 1 pt. One PR (MS stable and 10 Muts/Mb) and 7 SD16+ were observed for DC and OR rates of 28% (90% CI, 16% to 45%) and 4% (95% CI, 0% to 19%), respectively. 2 pts each had grade 3 AEs at least possibly related to P including abdominal infection, anorexia, colitis, diarrhea, fatigue, nausea, and vomiting; 1 also had SAE of acute kidney injury. Conclusions: Monotherapy with P showed anti-tumor activity in heavily pre-treated CRC pts with HTMB . Additional study is warranted to confirm the efficacy of P in this population. Clinical trial information: NCT02693535. [Table: see text]