Spontaneous regression of transverse colon cancer with high-frequency microsatellite instability: a case report and literature review

• Main Authors: Nozomi Karakuchi, Manabu Shimomura, Kazuhiro Toyota, Takao Hinoi, Hideki Yamamoto, Seiji Sadamoto, Koichi Mandai, Hiroyuki Egi, Hideki Ohdan, Tadateru Takahashi
• Format: Article
• Language: English
• Published: BMC 2019-01-01
• Series: World Journal of Surgical Oncology
• Subjects: Colorectal cancer; Spontaneous regression; Microsatellite instability
• Online Access: http://link.springer.com/article/10.1186/s12957-018-1552-x

Abstract Background Spontaneous regression (SR) of colorectal cancer (CRC) is extremely rare, and only few cases have been reported. Although it is not yet clarified, a plausible mechanism for SR of CRC is an immunological event. Case presentation In this report, we present the case of SR of primary CRC in a 78-year-old man. Preoperative colonoscopy was performed, and a type 2 tumor measuring 30 mm in diameter in the transverse colon was detected. The biopsy revealed a poorly differentiated adenocarcinoma. Colectomy was performed 2 months after initial colonoscopy. During the surgery, only a 10-mm ulcer harboring a polypoid lesion measuring 8.5 mm was detected in the resected tissue; no other masses or carcinoma cells were seen on histological examination. Afterwards, the biopsy specimens were reanalyzed, and immunohistological analysis verified this as adenocarcinoma with stroma-infiltrating lymphocytes. Further analysis revealed a loss of two mismatch repair proteins, suggesting sporadic high-frequency microsatellite instability (MSI-H). Conclusion According to previous literature, a common site of SR in CRC is the proximal colon, which is a feature of MSI-H CRC. However, our report showed a rare case of SR of CRC, which was in the transverse colon, with MSI-H present. This report indicates a relationship between immunological features of MSI-H and the occurrence of SR of CRC. A better understanding of this phenomenon and the mechanisms involved will have significant preventive and therapeutic implications for CRC, including anti-PD-1 immune checkpoint inhibitor therapy.