Clinicopathologic characteristics of patients with early-onset colorectal cancer.

Abstract

74 Background: Although the incidence of colorectal cancer has been declining in the United States in recent years, the incidence of young patients under 50 years of age has been reported to be increasing by several percent per year. Various studies have been conducted to characterize early-onset colorectal cancer (EO-CRC); however, it has been unclear whether it is a different entity from late-onset colorectal cancer (LO-CRC). In this study, we evaluated the clinicopathologic characteristics of EO-CRC in Japan. Methods: This study included 1,336 patients who underwent surgical resection for colorectal cancer at Tokyo Metropolitan Komagome Hospital from January 2015 to December 2019. We performed genetic testing for patients with suspected Lynch syndrome after providing genetic counseling and obtaining informed consent. The study protocol was approved by the Institutional Review Board. Results: Of the 1,336 colorectal cancer patients, 117 (8.9%) had EO-CRC with a median age at the diagnosis of 44 (17–49) years. Tumors were located at right-sided colon in 23 patients and left-sided colorectum in 92 patients with EO-CRC, respectively. The clinical stage of the tumor was I in 19, II in 23, III in 50, and IV in 23 patients with EO-CRC, respectively. Histologically, differentiated type, undifferentiated type, and mucinous carcinoma were 106, 5, and 3 patients, respectively. KRAS mutation was detected in 25.0% and BRAF V600E was detected in 4.3% of patients with EO-CRC. In the microsatellite status, MSI-High was detected in 6 (5.1%) patients with EO-CRC, of whom 3 (2.6%) were diagnosed with Lynch syndrome by genetic testing. Causative genes were MLH1 in 2 patients and MSH2 in one patient. In hereditary tumors, 2 patients with familial adenomatous polyposis were included in addition to Lynch syndrome. On the other hand, 1,219 (91.2%) had LO-CRC with 34.5% of KRAS mutation and 6.4% of BRAFV600E. MSI-High was detected in 69(5.7%) patients with LO-CRC，of whom 5 (0.4%) were diagnosed with Lynch syndrome. Lynch syndrome was significantly more common in EO-CRC (p=0.026). Conclusions: The alterations of KRAS and BRAF tended to be more frequent in EO-CRC. The frequency of hereditary CRC was more frequent in EO-CRC than in LO-CRC.