Management of small T1a/b breast cancer by tumor subtype

The treatment of patients with small (T1a/b) breast cancer is based on retrospective analysis. The influence of intrinsic tumor subtypes on patients' outcome and treatment decision remains unclear.

This is a prospective cohort register study including 1008 patients with small T1a/b breast cancer treated between 2003 and 2011. Tumors were grouped by biological characteristics into four different subtypes: luminal A, luminal B, human epidermal growth factor receptor 2 (HER2)-enriched, and triple-negative breast cancer (TNBC).

The median follow-up time was 6.5 years. From 919 eligible patients, 408 (44.4%) were classified as luminal A, 246 (26.8%) as luminal B, 183 (19.9%) as HER2 enriched, and 82 (8.9%) as TNBC. A total of 305 (34.2%) patients were treated with systemic therapy. Patients receiving systemic therapy were significantly younger and had lymph node metastasis, higher tumor grade, negative HR, and positive HER2 status. Patients with luminal A tumors demonstrated the best survival rate which improved with systemic therapy. The survival rate of patients with luminal B cancer, HER2-enriched tumors, and TNBC improved by addition of systemic treatment. The effect of systemic treatment was significant in luminal B (p = 0.040) and HER2 overexpressing tumors (p = 0.016). The treatment effect of systemic therapy in HER2-enriched tumors remained significant even after adjustment of other prognostic factors (HR 0.43, CI 0.19-0.98; p = 0.047). Notably, tumor size was not associated with patients' survival and treatment decision.

The treatment decision of small breast cancer should be made by biological subtype and not by tumor size or lymph node status.