Breast skin merkel cell carcinoma: a case report.

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin malignancy characterized by high recurrence and metastasis rates. Here, we present a case of primary breast skin MCC in a 65-year-old female patient who initially presented with a peanut-sized lump on her right breast, which rapidly developed into a cauliflower-like mass accompanied by intermittent pain. The patient underwent radical surgery (right mastectomy and right axillary lymph node dissection), followed by postoperative chemotherapy. Immunohistochemical examination revealed positive staining for Cytokeratin 20 (CK20), Synaptophysin (Syn), Cluster of Differentiation 56 (CD56), and Chromogranin A (CgA), confirming the diagnosis of MCC. A subsequent Positron Emission Tomography - Computed Tomography (PET-CT) scan revealed secondary liver metastasis. Despite an initial effective response to chemotherapy, the patient developed severe bone marrow suppression, necessitating a switch to maintenance therapy with capecitabine.