Abstract 510P
Background
Patients with localized dMMR GI cancer occasionally receive immunotherapy (IO) as primary treatment due to various clinical considerations. This study assesses the efficacy and safety of IO in this patient cohort.
Methods
The DREAM-GI national database was initiated to evaluate outcomes of patients with localized dMMR GI cancer patients who were surgically unfit or unresectable and received IO in a real-world setting. Retrospective data collection was conducted through March 31, 2024.
Results
Thirty-six patients (median age: 68 years, range 39-90) were included, with localized dMMR colorectal (53%), pancreaticobiliaryduodenal (36%), and gastroesophageal (11%) cancers; 13 (36 %) were female, 8 (22%) were Black, and the remaining were White. IO regimens included pembrolizumab (81%), ipilimumab plus nivolumab (11%), and chemoimmunotherapy (8%). Most patients (70%) were treatment-naive. The median duration of IO was 4.5 (1.5-24) months; time to best response was 3 months. Among 35 evaluable patients, 5 (14%) eventually underwent surgery following tumor shrinkage, with 4 (80%) achieving pathologic complete response (CR). Overall response rate (ORR) was 77% (n=27), including radiologic and/or endoscopic CR of 46% (n=16), pathologic CR of 12% (n=4), and partial response (PR) of 20% (n=7). Stable and progressive diseases were observed in 11% (n=4) each. The median progression-free and overall survival, calculated from the date of the first IO dose to the date of the last follow-up or death, did not reach after a median follow-up of 13 months (range: 2-102). ORR was 90% in colorectal and 62% in pancreaticobiliaryduodenal cancer. Among 16 patients achieving radiologic and or endoscopic CR, all remained progression-free after a median follow-up of 19 (4-102) months. Among the patients achieving PR, 2 had subsequent disease progression. Among deceased patients, causes included pneumonitis (n=1), disease progression (n=5), and comorbidities (n=4).
Conclusions
Majority of surgically unfit patients with localized dMMR GI cancer achieve deep and durable responses with IO alone. Colorectal cancer patients appear to exhibit a higher response rate.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.