Management of small T1a/b breast cancer by tumor subtype

Background:

The influence of intrinsic tumor subtypes on outcome of patients with small (T1a/b) breast cancer remains still unclear.

Patients and methods:

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 in four different subtypes: luminal A, luminal B, human epidermal growth factor receptor 2 (HER2) enriched, and triple negative breast cancer (TNBC).

Results:

The median follow-up time was 6.5 years. From 919 eligible patients 408 (44.4%) were classified luminal A, 246 (26.8%) luminal B, 183 (19.9%) HER2 enriched, and 82 (8.9%) TNBC. A total of 305 (34.2%) patients were treated with systemic therapy. Patients receiving systemic therapy were significantly younger, had lymph nodes metastasis, higher tumor grade, negative HR and positive HER2 status. Patients with luminal A tumors demonstrated the best survival rate and it was improved by systemic therapy. In the opposite, the survival rate of patients with luminal B cancer, HER2 enriched tumors and TNBC was 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). 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.

Conclusion:

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