Long-Term Survival Outcomes of Patients with Small (≤ 1 Centimetre) Node-Negative HER2-Positive Breast Cancer Not Treated with Adjuvant Anti-HER2-Targeted Therapy: A 10-Year Follow-Up Study

Introduction Human epidermal growth factor receptor 2 (HER2) expression is considered an unfavourable prognostic factor in early breast cancer when the patients are not treated with HER2-targeted therapy. However, the long-term prognostic importance of HER2-expression in small (≤1 cm, stage pT1a-b), node-negative HER2+ breast cancer is still incompletely known. Methods A retrospective analysis was performed based on a prospectively collected database including patients with pT1 breast cancer operated at the Helsinki University Hospital, Finland, between March 2000 and April 2006. In this database, 44 patients with pT1a-bN0M0, HER2+ cancer, not treated with adjuvant anti-HER2-targeted therapy (the HER2+ group) and 291 pT1a-bN0M0, hormone receptor positive, HER2- negative cancers (the ER+/HER2- group) were identified and included in the study. Survival outcomes were analysed using the Kaplan-Meier method. Results The median follow-up time was 9.7 years after primary breast surgery. Ten-year distant disease-free survival (DDFS) was 84.0% in the HER2+ group and 98.2% in the ER+/HER2- group (p < 0.001). Ten-year overall survival was only 78.5% in the HER2+ group, but 91.7% in the ER+/HER2- group (p = 0.09). Conclusions Cancer HER2-status is strongly associated with unfavourable DDFS during the first decade of follow-up in patients with small (pT1a-bN0M0) breast cancer when adjuvant anti-HER2-targeted treatment is not administered.