Adjuvant chemotherapy for breast cancer patients with axillary lymph node micrometastases

Background The axillary lymph node status is one of the most important prognostic factors in patients with early breast cancer. However, the impact of axillary lymph node micrometastases on survival remains unclear. There are no consistent recommendations for adjuvant chemotherapy (CHT). In this context, we aimed to investigate the impact of micrometastases on the clinical outcome of breast cancer patients according to the adjuvant CHT performed. Patients and methods We conducted a retrospective population-based registry study of 26,465 patients aged between 24 and 97 years with primary breast cancer diagnosed between 2003 and 2017. Of these patients, 8856 with early breast cancer were eligible for analysis: 8316 (93.9%) were node negative and 540 (6.1%) had lymph node micrometastases. Results The median follow-up was 7.2 years, with a confidence interval (CI) of 7.1–7.3 years. Patients with lymph node micrometastases (pN1mi) without adjuvant CHT have reduced 10-year overall survival (OS) and recurrence-free survival (RFS) compared to patients who had axillary lymph node micrometastases and received an adjuvant CHT. However, this effect disappeared after adjustment for age, tumor size and tumor grading. Furthermore, in the group of patients with lymph node micrometastases, the administration of adjuvant CHT did not improve OS or RFS, compared to patients with lymph node micrometastases without adjuvant CHT: hazard ratio for treated patients was 1.51 (95% CI 0.80–2.85, p = 0.208) for OS and 1.12 (95% CI 0.63–1.97, p = 0.705) for RFS. Conclusion Patients with axillary lymph node micrometastases showed a comparable outcome to node negative patients and their outcome was not significantly improved with CHT. Thus, axillary lymph node micrometastases should not be considered in the treatment decision.