Correlation of Tumour Subtype With Long-term Outcome in Small Breast Carcinomas: A Swedish Population-based Retrospective Cohort Study

Abstract Purpose: To investigate if molecular subtype is associated with outcome in stage 1 breast cancer (BC).Method: Tissue samples from 445 women with node-negative BC £15 mm, treated in 1986-2004, were classified into surrogate molecular subtypes (Luminal A-like, Luminal B-like, Her2-positive, and triple negative breast cancer (TNBC)). Information on treatment, recurrences and survival were gathered from medical records. Results: Tumour subtype was not associated with overall survival (OS). Luminal B-like and TNBC were associated with higher incidence of distant metastasis at 20 years. Luminal B-like and TNBC patients also had worse breast cancer specific survival (BCSS), although not statistically significant. Her2-positive BC was not associated with poor outcome despite no patient receiving Her2-targeted therapy.Conclusions: Stage 1 TNBC or Luminal B-like tumours behave more aggressively. Women with Her2+/ER+ tumours do not have an increased risk of distant metastasis or death, absent targeted treatment.