Pseudoprogression in patients treated with immune checkpoint inhibitors for microsatellite instability-high/mismatch repair-deficient metastatic colorectal cancer.

Background: The efficacy of immune checkpoint inhibitors (ICIs) in microsatellite instability-high/DNA mismatch repair (MSI/dMMR) metastatic colorectal cancer (mCRC) is well established. ICIs are responsible for pseudoprogression (PSPD) that complicates clinical decisions. We evaluated the PSPD frequency in patients with MSI/dMMR mCRC treated with ICIs.