Assessing Disease Control in Mismatch Repair-Proficient Colorectal Cancer With Peritoneal Metastases Treated With Immune Checkpoint Blockade-Based Combination Therapies

PURPOSE Metastatic colorectal adenocarcinoma (mCRC) with proficient mismatch repair (pMMR) is associated with poor response to cytotoxic chemotherapy in the refractory setting. Immunotherapy regimens using a combination of immune checkpoint blockade (ICB)–based combination therapies have shown promise, although few studies include patients with peritoneal metastases (PMs). This study sought to examine the disease control rate (DCR) and overall survival (OS) of patients treated with PM who were treated with ICB-containing regimens. METHODS Patients with pMMR metastatic colorectal cancer treated with ICB-based combination regimens after progression on first- and second-line therapy at The University of Texas MD Anderson Cancer Center from 2015 to 2022 were identified. Disease response within each metastatic site was determined. OS and DCR were calculated. RESULTS A total of 30 patients with PM, with or without other metastases, had a median follow-up on an ICB containing regimen of 8.5 months and a median follow-up until death or censoring of 13.3 months. The median OS was 16.7 (10.0-Not reported) months, and 18-month survival was 47%. Among patients treated for ≥6 months, DCR at 6 months at each metastatic site was 20% (2/10) for liver, 68% for peritoneum (13/19, P = .02 v liver), 50% for lung (5/10, P = .35 v liver), and 0% for retroperitoneal adenopathy (0/2, P = 1.00 v liver). CONCLUSIONS Among patients with mCRC, ICB-based combination regimens can provide disease control in the peritoneum in the majority of patients, and median OS compares favorably to standard-of-care therapy in the refractory setting. Patients with peritoneal disease should be included in future ICB trials since treatment options are otherwise limited.