The accuracy of chemotherapy ascertainment among colorectal cancer patients in the surveillance, epidemiology, and end results registry program

Background: Surveillance, Epidemiology, and End Results (SEER) public research database does not include chemotherapy data due to concerns for incomplete ascertainment. To compensate for perceived lack of data quality many researchers use SEER-Medicare linked data, limiting studies to persons over age 65. We sought to determine current SEER ascertainment of chemotherapy receipt in two relatively large SEER registries compared to patient-reported receipt and to assess patterns of under-ascertainment. Methods: In 2011-14, we surveyed patients with Stage III colorectal cancer reported to the Georgia and Metropolitan Detroit SEER registries. 1301/1909 eligible patients responded (68% response rate). Survey responses regarding treatment and sociodemographic factors were merged with SEER data. We compared patient-reported chemotherapy receipt with SEER recorded chemotherapy receipt. We estimated multivariable regression models to assess associations of under-ascertainment in SEER. Results: Eighty-five percent of patients reported chemotherapy receipt. Among those, 10% (n = 104) were under-ascertained in SEER (coded as not receiving chemotherapy). In unadjusted analyses, under-ascertainment was more common for older patients (11.8% age 76+ vs. <9% for all other ages, p = 0.01) and varied with SEER registries (10.2% Detroit vs. 6.8% Georgia; p = 0.04). On multivariable analyses, chemotherapy under-ascertainment did not vary significantly by any patient attributes. Conclusion: We found a 10% rate of under-ascertainment of adjuvant chemotherapy for resected, stage III colorectal cancer in two SEER registries. Chemotherapy under-ascertainment did not disproportionately affect any patient subgroups. Use of SEER data from select registries is an important resource for researchers investigating contemporary chemotherapy receipt and outcomes.