Abstract
Background: Microsatellite instability (MSI) testing is not only an indicator of immune checkpoint inhibitor (ICI) use but also offers an important test regarding the use of adjuvant chemotherapy. However, the percentage of MSI-high (MSI-H) among colorectal cancer patients is low, so few reports have examined actual treatment strategies and prognosis after detecting MSIH. The purpose of this report is to investigate the background characteristics, clinical significance, and prognosis of patients with MSI-H using a Japanese real-world multicenter database. Case presentation: Seventeen patients diagnosed with MSI-H were examined. Ten patients had metastatic or recurrent colorectal cancer, including 3 had metastatic disease (to the peritoneum, brain, and paraaortic lymph nodes), 7 had recurrent disease after curative resection (4 local recurrences, 2 in lymph nodes, and 1 in the peritoneum). CEA was elevated in 6 patients (60%) and CA19-9 was elevated in 3 patients (30%). Two patients (20%) showed KRAS mutations, and 5 patients (50%) were BRAF-positive. ICIs were administered to 9 patients (90%). Among these, 4 patients (44%) achieved complete response, 3 patients (33%) achieved partial response, and 2 patients (22%) showed stable disease. One patient treated with pembrolizumab developed interstitial pneumonia. All patients who received ICIs achieved progression-free survival. Seven patients were after curative colorectal cancer surgery. MSI was measured in 4 cases to investigate the likely utility of adjuvant therapy and in 3 cases to rule out familial colorectal cancer due to a family history of colorectal cancer. One patient with stage III received AC, but no other stage II patients received AC. All patients remain alive without recurrent disease as of the end of the study period.
Conclusion: For patients with metastatic or recurrent colorectal cancer or after curative resection requiring adjuvant chemotherapy, it is important to ensure that MSI status is measured.
