Axillary Downstaging in Occult Primary Breast Cancer After Neoadjuvant Chemotherapy

Neoadjuvant chemotherapy (NAC) is increasingly used for clinically node-positive (cN+) tumors with intact primary breast cancer (IPBC) to downstage the axilla, and those who convert to cN0 may be eligible for sentinel lymph node biopsy (SLNB). Rates of axillary downstaging in occult primary breast cancer (OPBC) are unknown.

The aim of this study was to determine the frequency of nodal pathologic complete response (pCR) following NAC in a cohort of patients with OPBC.

Twenty-eight patients with stage II/III OPBC treated between January 2008 and December 2019 were identified. Twenty patients had cN1-3 OPBC, pretreatment lymph node needle biopsy, and received NAC; these constituted the study population. Treatment factors and nodal pCR rates were summarized by tumor subtype.

Median age at diagnosis was 54 years. Most patients presented with cN1 disease (75%) and ductal histology (80%). Nodal pCR was seen in 16/20 (80%) patients. Eight (40%) patients were triple negative, 6 (30%) were estrogen receptor-positive/human epidermal growth factor receptor 2-negative (ER +/HER2 -), and 6 (30%) were HER2 positive, with pCR rates of 88%, 50%, and 100%, respectively. Among the 15 patients who presented as cN1, 14 (93%) converted to cN0 following NAC. Of these, nine underwent SLNB and all achieved nodal pCR (100%).

In this small series, 80% of OPBC patients achieved nodal pCR following NAC. pCR rates varied by receptor profile, being lowest in the ER positive/HER2 negative group and highest in the HER2 positive group (50-100%); however, these rates are excellent and numerically exceed those in the literature for IPBC. Given the pCR rate, SLNB may be an option in select OPBC patients who downstage following NAC.