Patterns of Progression and Survival in Patients with dMMR/MSI-H Metastatic Colorectal Cancer Treated with Immunotherapy.

Immunotherapy has shown to be efficacious in patients with deficient mismatch repair (dMMR)/microsatellite instability-high (MSI-H) colorectal cancer (CRC). Unfortunately, there is still a population of patients who either do not respond or progress after prior response. Understanding the progression dynamics and outcomes based on the nature of disease progression (PD) is critical in this patient population. We performed a retrospective analysis of 166 patients with advanced dMMR/MSI-H CRC who received immunotherapy.

PD patterns were classified as intrinsic (progression at first restaging scan) or adaptive (progression after initial stable/responding disease) and as single organ or systemic. Progression was seen in 64 patients (38.6%) with single organ progression in 31 (48.4%) and systemic progression in 33 (51.5%). Intrinsic progression was seen in 32 patients (50%) and adaptive progression in 32 (50%). Patients with single organ progression had a longer median TTP (mTTP) and median OS (mOS) compared to patients with systemic progression (mTTP: 8.8 vs 4.0 months, p = 0.005; mOS: 65.9 vs 18.7 months, p = 0.023).

Patients with adaptive PD had a longer mTTP and mOS compared to patients with intrinsic PD (mTTP: 11.6 vs 1.9 months, p =