Trends in management and related outcomes for occult primary breast cancer.

Purpose: Occult Primary Breast Cancer (OPBC) is a rare clinical condition in which breast cancer is located within the axillary lymph nodes, but no primary tumor is identified in the breast. We evaluated trends of neoadjuvant chemotherapy (NAC) use and subsequent axillary procedures in OPBC as well as outcomes for these patients.

Methods: The National Cancer Database was used to identify adult women with cT0N1-3M0 breast cancer between 2012 to 2021 that underwent axillary lymph node surgery. Kaplan-Meier curves were used to evaluate survival between groups.

Results: 2759 patients met inclusion criteria. 86.2% underwent ALND alone in 2012, and this decreased to 65.6% in 2021. 4.7% underwent SLNB alone in 2012 and this increased to 16.2% in 2021 (p < 0.001). For patients who had undergone NAC, 46.4% of ALND patients had nodal pathologic complete response (nPCR), compared to 42.7% of SLNB + ALND and 66.4% of SLNB only patients. For patients with nPCR, there was no difference in overall survival (OS) between ALND, SLNB + ALND, and SLNB alone groups (p = 0.9912).

Conclusion: Most OPBC patients were treated with ALND, with a modest increase towards SLNB use during the study period. There was no difference in OS with respect to axillary surgical procedure in our population for those with nPCR after NAC. This suggests that for carefully selected OPBC patients with an excellent clinical response to NAC and negative SLNB, omission of ALND may be considered.