Immune checkpoint inhibitors (ICI) have shown great promise in treating advanced or metastatic colorectal cancer (mCRC), especially for CRC patients with deficient mismatch repair (dMMR) and high microsatellite instability (MSI-H). For the remainder of CRC patients presenting with proficient mismatch repair (pMMR) and microsatellite stable (MSS) or low microsatellite instability (MSI-L), ICI showed a low-level response. This study describes a 57-year-old Chinese man diagnosed with pMMR MSS IVb CRC with liver metastasis. Primarily, the patient was administered two consecutive treatments, one composed of an anti-EGFR and modified FOLFOX6 and the other composed of an anti-VEGF and FOLFOXIRI. Due to severe chemotherapy side effects, the patient discontinued treatment and decided to take a third investigational treatment, where an anti-PD-1 and an anti-VEGF were given in combination with fecal microbiota transplantation (FMT) capsules. The patient achieved a partial response (PR), and the tumor size decreased to the extent amenable to surgical resection. After surgery, the patient achieved a pathological complete response (pCR). Patients with pMMR MSS or MSI-L hardly benefit from anti-PD-1 immunotherapy. This study indicated that, to a limited extent, FMT might improve the response to ICI for pMMR MSS CRC patients.
Keywords: gut microbiota transplantation; immune checkpoint inhibitor; metastatic colorectal cancer; pmmr mss crc; tumor microenvrionment.
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