Nivolumab in patients (pts) with advanced gastrointestinal (GI) cancers with high plasma tumor mutational burden (pTMB): Results from a SCRUM-Japan GOZILA phase II trial.

Abstract

98 Background: TMB is a biomarker for immune checkpoint inhibitors (ICIs). Analysis of circulating tumor DNA (ctDNA) has the potential to non-invasively identify pts likely to benefit from ICIs by assessing pTMB. We conducted a phase II basket trial as part of the SCRUM-Japan GOZILA umbrella/basket trial to evaluate the efficacy and safety of nivolumab monotherapy in pts with advanced GI cancers with high pTMB. Methods: Eligibility criteria included histologically confirmed unresectable or recurrent GI cancers; ECOG PS of 0 or 1; refractory or intolerant to the standard therapies; and high pTMB identified by Guardant360 CDx, a 74-gene ctDNA assay. Pts received intravenous nivolumab monotherapy of 360 mg every 3 weeks until progressive disease. The primary endpoint was objective response rate (ORR) per investigator assessment. The pTMB score was calculated by adjustment of mutation count by tumor fraction, and initial pTMB thresholds were determined based on previously reported ORR for ICI treatment for each GI cancer in the cohort. The cohort 2 proceeded only for esophageal cancer, and an ultra-high TMB cohort was created to include pts in the top 2% for pTMB scores. Results: Fifty-one pts with high pTMB in the cohort 1/2 (n=32) and the ultra-high TMB cohort (n=19) were enrolled. The median duration of follow-up was 7.5 months (range, 0.9–51.3). Deficient mismatch repair (dMMR) or high microsatellite instability (MSI-H) was observed in 1 pt in cohort 1/2 and 2 in ultra-high TMB cohort. The ORR was 12.5% and 21.1%, with median duration of response of 14.0 months and not reached, respectively. In an exploratory analysis of the overall population, pts with esophageal cancer had the highest ORR of 33.3% (4/12), followed by pancreatic (1/6, 16.7%) and colorectal cancer (3/27, 11.1%). Of 2 pts with proficient MMR/non-MSI-H colorectal cancer who had a response, 1 had a POLE mutation. Pts with response tended to have higher pTMB score (median, 26 vs. 8). dMMR/MSI-H (HR=0.16; 95% CI, 0.02–1.18), PD-L1 CPS ≥1 (HR=0.55; 95% CI, 0.29–1.01), and absence of liver metastasis (HR=0.36; 95% CI, 1.48–5.14) were significantly associated with longer progression-free survival. Treatment-related grade 3–4 adverse events occurred in 3 pts (9%) in the cohort 1/2 and 3 (16%) in the ultra-high TMB cohort, with no treatment death in either cohort. Conclusions: Nivolumab demonstrated antitumor activity in pretreated pts with advanced GI cancer and high pTMB. These results suggest that the use of pTMB potentially identify patients who may benefit from ICI treatment. Clinical trial information: UMIN000033182 .