Differences in subtype distribution between screen-detected and symptomatic invasive breast cancer and their impact on survival

Purpose: Stage shift is considered a major reason for more favorable outcomes in patients with screen-detected breast cancer. However, even after adjusting for clinical stage, unresolved issues concerning the reasons for a survival benefit associated with screening programs remain. This study aims to evaluate differences in subtype distribution and outcomes among patients with screen-detected and symptomatic invasive breast cancer and assess whether variations in subtype distribution could explain differences in prognosis. Methods: Survival analysis was performed to estimate the likelihood of distant recurrence and death in 1132 patients. Subtypes were defined as luminal A [estrogen receptor (ER)+ and/or progesterone receptor (PR)+, human epidermal growth factor receptor 2 (HER2)−, and Ki67 low], luminal B (HER2−) (ER+ and/or PR+, HER2−, and Ki67 high), luminal B (HER2+) (ER+ and/or PR+ and HER2+), HER2 overexpressing (ER−, PR−, and HER2+), and triple negative (ER−, PR−, and HER2−). Results: Screen-detected cancers had favorable clinicopathological characteristics, such as smaller tumor size and a lower frequency of lymph node involvement. Women with screen-detected cancers had a survival advantage. Subtype distribution differed significantly among women with screen-detected and symptomatic cancer. Screen-detected cancers were more likely to be luminal A and less likely to be HER2 overexpressing or triple negative cancer compared with symptomatic cancers (luminal A 61.3 vs. 44.2%, HER2 overexpressing 4.0 vs. 8.0%, triple negative 8.0 vs. 15.9%). Node status, mode of detection, and subtype were independent prognostic factors in the multivariate analysis. Conclusions: Differences in subtype distribution between screen-detected and symptomatic cancer could partially explain differences in outcomes.