Data extraction
tumor, CRC, Tumors, tumors, Cancer
DISEASES, TUMOR, TUMORS, TUMORS, RECTAL TUMORS, COLON TUMORS, CANCER
The CRC were coded as defined by the International Classification of Cancer Diseases (ICD-O-3). Codes C18.0 to C18.9 refer to colon tumors, C19.9 to rectosigmoid tumors and C20.9 to rectal tumors. All tumors were divided into 3 groups; right colon, left colon, and rectum. Tumors located between the cecum to the transverse colon were classified as right colon, while those located between the splenic flexure and the sigmoid colon were classified as left colon. Tumors encompassing the rectosigmoid junction and the rectum were classified as rectum. Patients were divided into 3 groups in accordance to the positional relationship of the multiple tumor lesions: unilateral group, bilateral group, and rectum-colon synchronous group. The unilateral group included patients with synchronous tumors located on one side (right-right colon, rectum-rectum, left-left colon), the bilateral group included patients with synchronous tumors on both sides (right-left colon, left–right colon), and the rectum-colon synchronous group included patients with synchronous tumors affecting the colon and the rectum (rectum-right colon; rectum-left colon). The lesion with the most advanced stage or size among the multiple lesions was used as the index tumor for analysis.