Prognostic analysis according to adjuvant chemotherapy and anti-HER2 therapy following surgery in T1a/b HER2-positive breast cancer

Background/Aims: The optimal adjuvant chemotherapy and anti-human epidermal growth factor receptor 2 (HER2) therapy regimen following surgery for T1a/b HER2-positive breast cancer remains debatable.Methods: In this single-center retrospective analysis, we examined the postoperative treatment strategies for patients diagnosed with T1a/b node-negative HER2-positive breast cancer. Invasive breast cancer-free survival (IBCFS), invasive disease-free survival, and overall survival (OS) were compared between patients who received chemotherapy only, chemotherapy plus anti-HER2 therapy, and neither adjuvant treatment.Results: The analysis included 165 patients, with a median follow-up duration of 98.4 (25.8–238.5) months. Patients who did not receive any adjuvant therapy had a 15-year IBCFS rate of 86.9%, and those who received only chemotherapy exhibited a rate of 77.6%. Conversely, those who received both trastuzumab and chemotherapy had the highest 15-year IBCFS rate of 97.4%, although the difference between the treatment groups was not statistically significant (<i>p</i> = 0.492). Among patients with T1a tumors, chemotherapy plus anti-HER2 therapy showed the most favorable long-term IBCFS, with a 15-year rate of 100%, compared with 57.5% in the chemotherapy-only group and 79.8% in the no-treatment group (<i>p</i> = 0.363). The 15-year OS rate was 100% in both chemotherapy-containing treatment groups, compared with 90.4% in the no-treatment group (<i>p</i> = 0.068).Conclusions: In this retrospective cohort of patients with HER2-positive T1a/bN0 breast cancer, anti-HER2-containing adjuvant treatment was associated with numerically favorable long-term outcomes, particularly among those with T1a tumors. Given the retrospective study design and limited number of events, these findings should be interpreted cautiously.