Long-Term Outcomes of Immunohistochemically Defined Subtypes of Breast Cancer Less Than or Equal to 2 cm After Breast-Conserving Surgery

Abstract Background Molecular subtype predicts the prognosis of early-stage breast cancer patients. We assessed the long-term outcomes of breast cancer ≤2 cm treated with breast-conserving surgery (BCS) and stratified according to an immunohistochemically (IHC)-based subtype definition. Methods This retrospective study was conducted from a prospectively collected database. Included patients had pT1, any N, M0 breast cancer after BCS (without anti-HER2 therapy) and available information on estrogen receptor (ER), progesterone receptor (PR), HER2 status, Ki-67 index. Five IHC-defined subtypes were identified: luminal A-like (ER and/or PR-positive/HER2-negative/Ki-67  Results We analyzed 184 (65%) luminal A-like, 57 (20%) luminal B-like/HER2-negative, 17 (6%) luminal B-like/HER2-positive, 6 (2%) HER2-positive/nonluminal, and 18 (7%) triple-negative patients. Median follow-up was 112 (interquartile range 94-125) mo. The cumulative 5- and 10-y local recurrence (LR) rates were 1.5% and 4%, respectively. The cumulative 5- and 10-y distant recurrence (DR) rates were 3% and 8%, respectively. The Cox regression revealed that HER2-positive/nonluminal subtypes had the highest risk of LR ( P  = 0.0025). The luminal B-like/HER2-positive subtypes had the highest risk of DR ( P  = 0.0019). HER2 positivity carried a higher risk of DR in women with luminal breast cancer who completed 5 y of adjuvant hormonal therapy ( P  = 0.02). Conclusions The IHC-defined subtype impacts on the prognosis of breast cancer ≤2 cm after BCS, determining significant differences in LR and DR rates. In the pre–“anti-HER2 therapy” era, patients with HER2-positive/nonluminal or luminal B-like/HER2-positive subtype had worse long-term outcomes than those with luminal A-like subtype.