Would 1.0 cm be a more suitable cutoff to subdivide pT1 tumors in hormone receptor-negative and HER2-positive breast cancer?

Background HER2+ and hormone receptor (HoR)-negative breast cancer usually associated with poor outcome. However, it remained elusive for the prognosis of small (T1a-T1c) HER2+/HoR- breast cancer. The present study retrospectively analyzed the Surveillance, Epidemiology, and End Results (SEER) database to explore the clinicopathological characteristics and prognosis of T1a-T1c HER2+/HoR- breast cancer. Material and Methods Data for patients diagnosed with either HER2-/HoR+or HER2+/HoR- T1a-T1c breast cancer between 2010 and 2012 were obtained from SEER program. Survival analyses were conducted by Kaplan-Meier method and Cox proportion hazard regression. Results Totally, 2648 HER2+/HoR- and 56387 HER2-/HoR+T1a-T1c breast cancer patients were enrolled. There was a clear trend that tumor size had a positive correlation with advanced AJCC stage (P < 0.001) and N-stage (P < 0.001). T1a and T1b HER2+/HoR- breast cancer had great homogeneity in that these two subgroups had comparable survival and both showed no significant survival difference with its counterpart of HER2-/HoR+subtype. Conversely, T1c HER2+/HoR- breast cancers revealed worse prognosis than T1a/T1b HER2+/HoR- and T1c HER2-/HoR+tumors (BCSS HR 3.847, P < 0.001; OS HR 2.055, P < 0.001). Conclusion T1a and T1b HER2+/HoR- breast cancer had favorable prognosis and great homogeneity, indicating 1.0 cm may be a suitable cutoff for subclassification of T1 cancer. Future randomized clinical trials were warranted to verify this hypothesis and elucidate the biological behavior of small T1 tumor to facilitate precise medicine.