Metastatic Cutaneous Apocrine Carcinoma: Diagnostic and Therapeutic Challenges in a Rare Malignancy.

Cutaneous apocrine carcinoma is a rare adnexal malignancy with limited evidence guiding treatment in the metastatic setting. We present the case of a 50-year-old man with hormone receptor-positive metastatic cutaneous apocrine carcinoma of the right axilla initially treated with surgical excision, nodal resection, and adjuvant radiation therapy. He later developed metastatic recurrence involving the spine and lungs, requiring surgical stabilization. Molecular profiling demonstrated a KMT2C mutation, microsatellite-stable disease, low tumor mutational burden, and overexpression of ERBB2 (Erb-B2 receptor tyrosine kinase 2/HER2), ERBB3 (Erb-B3 receptor tyrosine kinase 3/HER3), NFKB1 (nuclear factor kappa B subunit 1), CCND1 (cyclin D1), RET (RET proto-oncogene receptor tyrosine kinase), and AR (androgen receptor) pathways, while immunohistochemistry showed strong estrogen receptor positivity, androgen receptor expression, and HER2 negativity (unusual given the ERBB2 positivity). The patient later received sequential therapy with tamoxifen, pembrolizumab, androgen deprivation therapy, and, most recently, palliative radiation, followed by carboplatin/paclitaxel for progressive disease complicated by spinal cord compression. His clinical course was further complicated by severe neutropenia, radiation esophagitis, and chemotherapy-induced peripheral neuropathy. This case highlights the therapeutic complexity of metastatic cutaneous apocrine carcinoma and demonstrates the potential for meaningful disease control with endocrine and immune-based therapies despite progression through multiple lines of treatment. Given the absence of a standard treatment paradigm, more investigation in larger cohorts is needed to validate the role of these treatment approaches in improving outcomes in metastatic apocrine carcinoma.