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

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.

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.

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).

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.