Outcomes and treatment patterns for stage I human epidermal growth factor receptor 2-positive breast cancer in the Surveillance, Epidemiology, and End Results database, 2010-2019.

BACKGROUND

The risk of recurrence in patients with small, lymph node-negative, human epidermal growth factor receptor 2 (HER2)-positive breast cancers untreated with adjuvant chemotherapy/HER2-directed therapy is uncertain. To investigate this, the authors conducted a retrospective, population-based study of chemotherapy use and breast cancer-specific survival (BCSS) among patients with stage IA HER2-positive breast cancer.

METHODS

The authors analyzed Surveillance, Epidemiology, and End Results data from patients diagnosed with stage IA HER2-positive breast cancer from 2010 to 2019. They examined the frequency of chemotherapy use by tumor size and hormone receptor (HR) status and applied multivariate logistic regression to assess the factors associated with receipt of chemotherapy. BCSS was evaluated and performed multivariable Cox regression was performed to evaluate the association between chemotherapy receipt and BCSS.

RESULTS

Among 12,896 patients, 74.0% had HR-positive/HER2-positive breast cancer, and 26.0% had HR-negative/HER2-positive breast cancer. Adjuvant chemotherapy was received by to 58.9% of patients, with lower utilization for those who were older, Hispanic or Asian/Pacific Islander, separated/divorced/widowed, or had a lower median household income. The median follow-up was 46 months. Among the patients who had pathologic T1 (pT1) microscopic, pT1a, or pT1b tumors, the 5-year BCSS rate was 97.6%-99.6% in those who had no evidence of chemotherapy receipt in the medical record versus 98.4%-100.0% in those who did receive chemotherapy. Among patients who had pT1c tumors and had no evidence of chemotherapy receipt, the 5-year BCSS rate was 92.1% for those with HR-negative/HER2-positive breast cancer and 96.0% for those with HR-positive/HER2-positive breast cancer. Patients who had pT1c tumors and received chemotherapy had a 5-year BCSS rate of 96.7% in those with HR-negative/HER2-positive breast cancer and 98.7% in those with HR-positive/HER2-positive breast cancer.

CONCLUSIONS

In this large, population-based study of patients with stage IA HER2-positive breast cancer, patients who had tumors ≤1 cm had excellent outcomes with or without chemotherapy. Patients with pT1c tumors had a greater increase in BCSS with the receipt chemotherapy.