Adjuvant Chemotherapy Use and Adverse Events Among Older Patients with Stage III Colon Cancer

Context: Randomized trials suggest adjuvant chemotherapy is effective for older patients with stage III colon cancer. However, older patients are less likely to receive this therapy than younger patients, perhaps because of concern about adverse effects. Objective: To evaluate adjuvant chemotherapy use and outcomes for older patients with stage III colon cancer from well-defined population-based settings and health care systems. Design: Observational study of adjuvant chemotherapy use and outcomes by age using Poisson regression to estimate the number of adverse events adjusted for demographic and clinical factors, including comorbid illness and specific elements of chemotherapy regimens documented with clinically detailed medical record reviews and patient and surrogate surveys. Setting: Five geographically defined regions (Alabama, Iowa, Los Angeles County, northern California, and North Carolina), 5 integrated health care delivery systems, and 15 Veterans Affairs hospitals. Patients: Six hundred seventy-five patients diagnosed with stage III colon cancer from 2003 through 2005 who underwent surgical resection and were followed up for as long as 15 months postdiagnosis. Main outcome measures: Chemotherapy regimen, dose, duration, and annualized mean number of adverse events stratified by age. Results: Of 202 patients aged 75 years and older, 101 (50%) received adjuvant chemotherapy compared with 87% of 473 younger patients (difference, 37%; 95% confidence interval [CI], 30%-45%). Among patients who received adjuvant chemotherapy, 14 patients (14%) aged 75 years and older and 178 younger patients (44%) received a regimen containing oxaliplatin (difference, 30%; 95% CI, 21%-38%). Older patients were less likely to continue treatment, such that by 150 days, 99 patients (40%) aged 65 years and older and 68 younger patients (25%) had discontinued chemotherapy (difference, 15%; 95% CI, 7%-23%). Overall, 162 patients (24%) had at least 1 adverse clinical event, with more events among patients treated with vs without adjuvant chemotherapy (mean, 0.39 vs 0.16; difference, 0.23; 95% CI, 0.11-0.36; P < .001). Among patients receiving adjuvant chemotherapy, adjusted rates of late clinical adverse events were lower for patients 75 years and older (mean, 0.28) vs for younger patients (0.35 for ages 18-54 years, 0.52 for ages 55-64 years, and 0.45 for ages 65-74 years; P = .008 for any age effect). Conclusion: Among patients with stage III colon cancer who underwent surgical resection and received adjuvant chemotherapy, older patients in the community received less-toxic and shorter chemotherapy regimens, and those treated had fewer adverse events than younger patients.