Racial Disparities in Cancer Presentation and Outcomes: The Contribution of Overdiagnosis.

BACKGROUND: Racial disparities in cancer have been attributed to population differences in access to care. Differences in cancer overdiagnosis rates are another, less commonly considered cause of disparities. Here, we examine the contribution of overdiagnosis to observed racial disparities in papillary thyroid cancer and estrogen/progesterone receptor positive (ER/PR+) breast cancer. METHODS: We used Surveillance, Epidemiology, End-Results (SEER) 13 for analysis of white and black non-Hispanic persons with papillary thyroid cancer or ER/PR+ breast cancer (1992-2014). Analyses were performed using SeerStat (v8.3.5, March 2018). All statistical tests were two-sided. RESULTS: White persons had higher incidence of papillary thyroid cancer than black persons (14.3 vs 7.7 cases per 100 000 age-adjusted population) and ER/PR+ breast cancer (94.8 vs 70.9 cases per 100 000 age-adjusted population) (P < .001). In papillary thyroid cancer, the entire incidence difference was from more frequent diagnosis of 2-cm or less (10.0 vs 4.9 cases per 100 000 population) and localized or regional (13.8 vs 7.4 cases per 100 000 population) cancers in white persons (P < .001), without corresponding excess of metastatic disease, cancers greater than 4 cm, or incidence-based mortality in black persons. In women with ER/PR+ breast cancer, 95% of the incidence difference was from more 2-cm or less (61.2 vs 38.1 cases per 100 000 population) or 2.1- to 5-cm (25.4 vs 23.4 cases per 100 000 population), localized (65.1 vs 43.0 cases per 100 000 population) cancers diagnosed in white women (P < .001), with slightly higher incidence of tumors greater than 5 cm (10.1 vs 9.3 cases per 100 000 population, P < .001) and incidence-based mortality (8.1 vs 7.2 cases per 100 000 population, P < .001) among black women. Overall, 20-30 additional small or localized ER/PR+ breast cancers were diagnosed in white compared with black women for every large or advanced tumor avoided by early detection. Overdiagnosis was estimated 1.3-2.5 times (papillary thyroid cancer) and 1.7-5.7 times (ER/PR+ breast cancer) higher in white compared with black populations. CONCLUSIONS: Differences in low-risk cancer identification among populations lead to overestimation of racial disparities. Estimates of overdiagnosed cases should be considered to improve care and eliminate disparities while minimizing harms of overdiagnosis.