E72: Assessment of Axillary De-escalation Following Neoadjuvant Chemotherapy in Occult Primary Breast Cancer

Introduction: Occult Primary Breast Cancer (OPBC) is a distinct form of breast malignancy characterized by axillary metastatic carcinoma without a detectable primary breast lesion. It accounts for less than 1% of newly diagnosed cases. Traditionally, axillary lymph node dissection (ALND) had been considered standard of care for patients with OPBC. This study aims to evaluate the potential for less invasive axillary treatments by identifying factors associated with an axillary pathologic complete response (pCR) to neoadjuvant chemotherapy (NCT) in the setting of OPBC.

Methods: A retrospective analysis of the National Cancer Data Base (NCDB) was performed to evaluate women diagnosed with clinically node-positive OPBC between 2012 and 2020. All patients underwent NCT followed by ALND. Axillary pCR was defined according to the AJCC criteria. Descriptive statistics were used to analyze clinical practice trends, Chi-square tests were used to assess categorical variables, and logistic regression analyses were used to identify associations with ypN0 disease.

Results: This retrospective cohort study consisted of 150 women who underwent NCT followed by ALND for OPBC. Among these patients, 15 (10%) achieved axillary pCR. An increase in axillary pCR rate was observed with triple negative breast cancer and HER2-positive receptor status (13.3% and 28.2% respectively, p< 0.001). No other factors were significantly associated with axillary pCR.

Conclusions: The findings indicate that certain patients with OPBC who undergo NCT can achieve an axillary pCR, potentially qualifying them for less invasive surgical options. Variability in axillary pCR was predominantly influenced by receptor status, suggesting that alternative surgical approaches such as targeted axillary dissection may be a feasible option for select patients with OPBC who show a favorable response to NCT.