Eccrine Carcinoma Mimicking Breast Cancer: Diagnostic Challenges and Hormone Therapy as an Emerging Treatment.

Eccrine carcinoma is an exceedingly rare malignancy originating from the eccrine sweat glands, representing less than 0.01% of all cutaneous malignancies. The diagnosis of eccrine carcinoma is challenging due to its rarity. Its morphological similarities with other common tumors, especially breast cancer, further complicate assessment. It is crucial to differentiate eccrine carcinoma from metastatic breast cancer. In addition, the standard treatment is also not well established. We present the case of a 66-year-old female with a lesion on her left lip. Initially identified in 2017, the lesion recurred in 2020 and 2023. Surgeries in 2017 and 2020 achieved R0 resections, while the 2023 recurrence was an R2 resection with lymph node metastasis. Pathology suggested a possible primary breast ductal carcinoma. Immunostains were positive for estrogen receptor (ER) and progesterone receptor (PR). However, positron emission tomography/computed tomography (PET/CT) did not reveal any primary breast lesion, and there was no accessory breast tissue involvement, leading to a diagnosis of primary eccrine carcinoma. The patient declined chemotherapy and radiation therapy, opting instead for treatment with letrozole and ribociclib. Six-month follow-up imaging showed reduced lymph node size, suggesting a favorable response to therapy. This case highlights the diagnostic challenges of eccrine carcinoma, given that it mimics malignancies like breast cancer. Hormone therapy may be a potential option for hormone receptor-positive cases. Further research is essential to develop clearer diagnostic tools and standardized treatment protocols for this rare malignancy.