Clinicopathological features of post-colonoscopy colorectal cancer in patients with Japanese Lynch syndrome: A multicentric retrospective observational study.

Abstract

79 Background: Due to the high incidence of heterochronic and concurrent colorectal cancer in Lynch syndrome (LS), colonoscopic surveillance is recommended in Japan every 1-2 years. Even with regular colonoscopic surveillance, post-colonoscopy colorectal cancer (PCCRC) often occurs in the intervals between surveillance, but there are currently no reports of the details of PCCRC in LS in Japan. Methods: Of 1756 colonoscopies performed between 2009 and 2018 in 316 patients with a diagnosis of LS confirmed by genetic testing who were enrolled in a nationwide, Japanese, multicentric study conducted by the Committee of Hereditary Colorectal Cancer of the Japanese Society for Cancer and Rectum, 1203 colonoscopies in 256 patients were assessed to determine the clinicopathological characteristics of PCCRC, after including cases of first-time surveillance, previously untreated lesions, and inadequate pretreatment. Then, the incidence of PCCRC was compared between patients with a median surveillance colonoscopy interval < 12 months (group A) and > 12 months (group B). Results: There were 49 cases of PCCRC with a total of 84 lesions. The number of lesions per tumor depth was 66, one, five, seven, four, and one for pTis, pT1, pT1a, pT1b, pT2, and pT3, respectively. Two (2.4%), 20 (23.8%), 21 (25%), four (4.8%), 18 (21.4%), and 19 (22.6%) lesions were localized in the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum, respectively. In pTis-pT1b, the macroscopic type was 0-IIa in 33 lesions (41.8%), 0-IIc in four lesions (5.1%), 0-IIa+IIc in five lesions (6.3%), 0-IIb in one lesion (1.3%), 0-Is in 15 lesions (19%), 0-Ip in one lesion (1.3%), 0-Isp in 16 lesions (20.3%), and unknown in four lesions. In pT1b-pT3, seven lesions (63.6%) were smaller than 20 mm. In terms of the median interval between surveillance colonoscopies, 130 patients had a median interval < 12 months (group A), and 126 patients had a median interval > 12 months (group B). In groups A and B, PCCRC, metachronous cases, simultaneous cases, and depths than pT1b were observed in 29 (22%) and 20 (16%) cases (p=0.21); 14 (11%) and two (1.6%) cases (p=0.006); six (4.6%) and one (0.8%) case (p=0.22), and six (4.6%) and four (3.2%) cases (p=1), respectively. Conclusions: In PCCRC in Lynch syndrome, invasive carcinomas < 2 cm should be noted. In addition, a surveillance interval of 12 months may be insufficient in patients with LS. Thus, further investigation is warranted.