Eccrine Carcinoma With an Unknown Primary: Managing Occult Cancer Through Multidisciplinary Tumor Board Collaboration.

Eccrine carcinomas are rare cutaneous cancers that tend to be locally aggressive. Here we report a rare case of a mucinous eccrine carcinoma presenting in axillary lymph nodes without an identifiable primary lesion. This is a 69-year-old male with a past medical history of benign prostatic hyperplasia, melanoma, basal cell carcinoma, hypercholesterolemia, hypertension, and arthritis who was found to have an elevated prostate-specific antigen. Transrectal prostate biopsies confirmed adenocarcinoma of the prostate. A chest CT scan performed for further staging of prostate cancer identified new left axillary lymphadenopathy and positron emission tomography (PET)-CT imaging showed moderate fluorodeoxyglucose (FDG) uptake in the lymph nodes of the left axilla and left subpectoral regions. Lymph node tissue obtained by core needle biopsy demonstrated high-grade carcinoma with a nonspecific immunohistochemical profile. Complete left axillary lymphadenectomy was performed, revealing mucinous eccrine carcinoma. He was started on hormonal therapy for prostate cancer and radiation therapy for axillary eccrine carcinoma at the same time. Based on our literature review, this appears to be the first case of eccrine carcinoma in axillary lymph nodes with an unknown primary. This case is further complicated by synchronous primary prostate cancer. After a multidisciplinary tumor board review, it was decided that his axillary disease should be treated as a primary mucinous carcinoma with complete lymphadenectomy followed by localized radiation. The patient had stable disease at the six-month follow-up. Cancers with unknown primary lesions pose unique challenges in disease management. Without established recommendations or guidelines, multidisciplinary discussions and a collaborative approach are needed.