Objective:To investigate the clinicopathological characteristics of early-onset colorectal cancer.Methods:The retrospective and descriptive study was conducted. The clincopatholo-gical data of 59 206 patients with colorectal cancer in the Surveillance, Epidemiology, and End Results Program of the United States of America From January 1,2010 to December 31,2019 were collected. There were 33 213 males, 25 993 males, aged (50±7)years. Observation indicators: (1) demographic and oncological characteristics of colorectal cancer patients; (2) comparison of clinico-pathological characteristics between early-onset and late-onset colorectal cancer. Measurement data with normal distribution were represented as Mean± SD, and comparison between groups was conducted using the t test. Measurement data with skewed distribution were represented as M( Q1, Q3), and comparison among groups was conducted using the Kruskal-Wallis H test. Count data were described as absolute numbers, and comparison among groups was conducted using the chi-square test. Comparison of ordinal data was conducted using the non-parameter H test. Patients with early-onset colorectal cancer were segmented by age, and missing data for categorical variables is set as unknown. Results:(1) Demographic and oncological characteristics of colorectal cancer patients. Of 59 206 patients, there were 23 104 cases with early-onset colorectal cancer and 36 102 cases with late-onset colorectal cancer, and cases aged 13-29 years, cases aged 30-34 years, cases aged 35-39 years, cases aged 40-44 years, cases aged 45-49 years, cases aged 55-59 years were 1 041, 1 740, 3 288, 6 050, 10 985, 15 303,20 799, respectively. (2) Comparison of clinicopathological charac-teristics between early-onset and late-onset colorectal cancer. ① There were significant differences in gender, tumor location, degree of tumor differentiation, tumor histological type, tumor TNM staging, tumor T staging, tumor N staging, tumor M staging, preoperative carcinoembryonic antigen (CEA), perineural invasion, cancer nodule, tumor diameter between patients with early-onset and late-onset colorectal cancer ( P<0.01). Results of further analysis showed that cases with tumor located in ileocecal region, ascending colon, colon liver region, transverse colon were 2 329, 2 139, 579, 1 303 in the 6 350 patients with early-onset right colon cancer. The above indicators were 4 563, 3 945, 902, 1 951 in the 11 361 patients with late-onset right colon cancer. There was a significant difference in the above indicators between the two groups of patients ( χ2=114.27, P<0.01). Cases with tumor located in splenic region of the colon, descending colon, sigmoid colon, rectum sigmoid junction were 553, 1 354, 6 404, 2 431 in the 10 742 patients with early-onset left colon cancer. The above indicators were 865, 1 798, 9 668, 3 610 in the 15 941 patients with late-onset left colon cancer. There was a significant difference in the above indicators between the two groups of patients ( χ2=35.60, P<0.01). ②Of 23 104 patients with early-onset colorectal cancer, cases aged 13-29 years, cases aged 30-34 years, cases aged 35-39 years, cases aged 40-44 years, cases aged 45-49 years were 1 041, 1 740, 3 288, 6 050, 10 985, respectively. There were significant differences in gender, degree of tumor differentiation, tumor histological type, tumor TNM staging, tumor T staging, tumor N staging, pre-operative CEA, perineural invasion, cancer nodule, tumor diameter among patients of different age groups ( P<0.01). Results of further analysis showed that cases with tumor located in ileocecal region, ascending colon, colon liver region, and transverse colon were 91, 117, 45, 69 in the 6 350 early-onset right colorectal cancer patients aged 13-29 years. The above indicators were 165, 136, 47, 115, 304, 313, 93,201, 614, 535, 151, 330, 1 155, 1 038, 243, 588 in early-onset right colorectal cancer patients aged 30-34, 35-39, 40-44, 45-49 years, respectively. There was a significant difference in the above indicators among the five groups of patients ( H=36.63, P<0.01). Cases with tumor located in splenic region of the colon, descending colon, sigmoid colon, rectum sigmoid junction were 32, 83, 260, 95 in the 10 742 early-onset left colorectal cancer patients aged 13-29 years. The above indica-tors were 53, 112, 452, 171, 95, 230, 867, 342, 149, 337, 1 702, 665, 224, 592, 3 123, 1 158 in the 10 742 early-onset left colorectal cancer patients aged 30-34, 35-39, 40-44, 45-49 years, respectively. There was a significant difference in the above indicators among the five groups of patients ( H=47.84, P<0.01). Conclusions:Compared with late-onset colorectal cancer, early-onset colorectal cancer are more likely to occur in the left colon and rectum, with poorly differentiated and undifferentiated tumors, histological type of mucinous adenocarcinoma, TNM staging of stage Ⅲ and Ⅳ, higher proportion of nerve infiltration and cancer nodules, and larger tumor diameter. There are significant differences in clinicopathological characteristics of tumors among patients with early-onset colorectal cancer of different age groups.