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

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. 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-). 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. Differences in subtype distribution between screen-detected and symptomatic cancer could partially explain differences in outcomes.