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

• Published in: World journal of surgical oncology 2019-01, Vol.17 (1), p.19-19, Article 19
• Main Authors: Karakuchi, Nozomi, Shimomura, Manabu, Toyota, Kazuhiro, Hinoi, Takao, Yamamoto, Hideki, Sadamoto, Seiji, Mandai, Koichi, Egi, Hiroyuki, Ohdan, Hideki, Takahashi, Tadateru
• Format: Article
• Language: English
• Subjects: Adenocarcinoma; Antigens; Biopsy; Cancer; Cancer regression; Care and treatment; Case Report; Case reports; Colon; Colon cancer; Colonoscopy; Colorectal cancer; Colorectal carcinoma; Development and progression; Endoscopy; Frequency stability; Genetic aspects; Health aspects; Immune checkpoint inhibitors; Immunology; Literature reviews; Lymphocytes; Microsatellite instability; Mismatch repair; PD-1 protein; Proteins; Regression analysis; Spontaneous regression; Stroma; Surgery; Tumors; Ulcers
• ISSN: 1477-7819; 1477-7819
• DOI: 10.1186/s12957-018-1552-x

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. 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). 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.