Cutaneous Adnexal Carcinoma with Apocrine Differentiation: A Challenging Diagnosis and Personalized Treatment with mTOR Inhibitor in a Very Rare Disease

Cutaneous adnexal carcinoma with apocrine differentiation is a rare neoplasm arising from cutaneous adnexa, especially of the head and neck and trunk region. Because of its rarity, the diagnosis is challenging and often impossible to distinguish from metastatic cutaneous adenocarcinoma of the breast. The standard of care remains surgery for resectable disease. To date, univocal guidelines for metastatic disease are lacking, particularly regarding systemic therapy. We report a clinical case of a patient diagnosed with cutaneous adnexal adenocarcinoma with apocrine differentiation of the left axilla with lymph node and bone metastasis. We started with carboplatin and paclitaxel chemotherapy regimen, with good response. After progression, we performed a next-generation sequencing analysis (by the Foundation One CDx test) to identify genomic alteration in cancer-related genes. We found PIK3CA and KRAS mutations. Due to this result, the patient started a second-line treatment with a personalized therapy including an mTOR inhibitor, everolimus, and, to date, he is still under treatment. To our knowledge, this is the first case of a patient responding both to chemotherapy and to a personalized treatment with an mTOR inhibitor. It is important to support the value of genomic screening in this rare neoplasm.