Prognosis and chemotherapy efficacy in small-tumor breast cancer with different immune subtypes: a SEER-based study.

Background: In the case of lymph node metastasis, small-tumor breast cancer patients show distinct survival rates. Current studies have not conducted in-depth analyses of small-tumor patients with different immune subtypes and different lymph node metastases. This study aimed to examine the survival outcomes and chemotherapy efficacy of patients with different immune subtypes. Methods: Retrospective clinical data of small-tumor breast cancer patients were obtained from the Surveillance, Epidemiology, and End Results (SEER) database. A multivariate Cox proportional hazards model was used to analyze prognostic factors. Survival analysis was stratified based on stage T, stage N and immune subtypes. Results: Patients with T1cN2+ stage had the highest risk of death. However, in T1N1 stage cancers, compared with patients of other subtypes in T1mi/a-bN1 stage, the overall survival (OS) and breast cancer-specific survival (BCSS) of patients with T1mi/a-bN1 hormone receptor negative human epidermal growth factor receptor 2 positive (HR-HER2+) were significantly worse. HR+HER2- subtype patients showed a similar trend. Additionally, postoperative adjuvant chemotherapy (AC) was a favorable prognostic factor for OS in small-tumor breast cancer patients [hazard ratio (HR) =0.78, P<0.001] but had no significant effect on BCSS (HR =1.1, P=0.11). In the pT1mi/a-bN0-1 HR+HER2- subtype and pT1mi/a-bN0 HR-HER2-/HR+HER2+ subtype patients, AC did not significantly improve survival (P>0.05). Conclusions: In addition to T1cN2+ stage or HR-HER2- subtype, this study identified T1mi/a-bN1 HR-HER2+ subgroup as a high-risk type in small-tumor breast cancer. And small-tumor breast cancer patients do not usually benefit from AC. AC may not be recommended for certain subgroups, such as patients with pT1mi/a-bN0-1 HR+HER2- or pT1mi/a-bN0 HR-HER2-/HR+HER2+ can be exempted from chemotherapy.