Apocrine adenocarcinoma in a patient with a partner and localizer of BRCA2 (PALB2) genetic mutation: A case report

Introduction: Apocrine adenocarcinoma is a rare malignant neoplasm involving apocrine sweat glands. Physical presentation is variable, as masses can be violaceous, erythematous, solid, cystic, nodular, or ulcerated. Due to its lack of distinctive physical features, immunohistochemical staining with clinical correlation is imperative to reach an accurate diagnosis. Case Report: A 72-year-old male presented with a painful, erythematous mass in the right axilla. A shave biopsy with immunohistochemical staining revealed estrogen receptor (ER) negative, progesterone receptor (PR) negative, human epidermal growth factor receptor 2 (HER2) negative results, suggesting ductal carcinoma of breast origin. However, follow-up imaging showed no breast abnormalities. A subsequent positron emission tomography (PET) scan showed hypermetabolic lymph nodes and cutaneous uptake in the right axilla. A right axillary lymph node biopsy showed ER negative, PR negative, HER2 positive, and α-methylacyl CoA racemase (AMACR), also known as p504s, positive results in immunohistochemistry, confirming the diagnosis of apocrine adenocarcinoma. Our patient underwent local excision of the primary tumor, neoadjuvant chemotherapy of a carboplatin paclitaxel regimen, a complete right axillary node dissection, and is undergoing maintenance chemotherapy with pembrolizumab. Conclusion: The diagnosis of apocrine adenocarcinoma is extremely rare, with less than 200 cases reported as of 2024. Our patient also has a partner and localizer of BRCA2 (PALB2) genetic mutation. To our knowledge, there are no reported cases of apocrine adenocarcinoma in a patient with a PALB2 genetic mutation. Standard treatment is wide local excision, with or without chemotherapy depending on lymph node involvement.