LAUSR

Importance Treatment options for patients with young-onset colon cancer remain to be defined and their effects on prognosis are unclear. Objective To investigate receipt of adjuvant chemotherapy by age category (18-49, 50-64, and 65-75 years) and assess whether age differences in chemotherapy matched survival gains among patients diagnosed as having colon cancer in an equal-access health care system. Design, Setting, and Participants This cohort study was based on linked and consolidated data from the US Department of Defense’s Central Cancer Registry and Military Heath System medical claims databases. There were 3143 patients aged 18 to 75 years with histologically confirmed primary colon adenocarcinoma diagnosed between 1998 and 2007. This study was conducted from December 2015 to August 2016. Exposures Patients who underwent surgery and postoperative systemic chemotherapy. Main Outcomes and Measures The primary outcome measure of the study was overall survival of patients who only received surgery and those who received both surgery and postoperative systemic chemotherapy. Results Of the 3143 patients, 1841 were men (58.6%). Young (18-49 years) and middle-aged (50-64 years) patients were 2 to 8 times more likely to receive postoperative systemic chemotherapy compared with older patients (65-75 years) across all tumor stages. Middle-aged patients with stage I (odds ratio, 5.04; 95% CI, 2.30-11.05) and stage II (odds ratio, 2.42; 95% CI, 1.58-3.72) disease were more likely to receive postoperative chemotherapy compared with older patients. Both groups were more likely to receive multiagent chemotherapy than were older patients (patients aged 18-49 years: odds ratio, 2.48; 95% CI, 1.42-4.32 and patients aged 50-64 years: odds ratio, 2.66; 95% CI, 1.70-4.18). Among patients who received surgery and postoperative systemic chemotherapy, no significant differences were observed in survival among age groups (the 95% CIs of hazard ratios included 1 for young and middle-aged patients compared with older patients for all tumor stages). Conclusions and Relevance In an equal-access health care system, we found potential overuse of chemotherapy among young and middle-aged adults with colon cancer. The addition of postoperative systemic chemotherapy did not result in matched survival improvement.