Melanoma Metastasis to a Pituitary Neuroendocrine Tumor: A Case Report and Literature Review

We report a 44-year-old man with a non-functioning pituitary macroadenoma diagnosed approximately 10 years before the current presentation.He subsequently developed metastatic amelanotic melanoma originating from a cutaneous lesion of the right auricle, with jejunal metastases.After disease progression despite immunotherapy and chemotherapy, he presented with visual disturbances and panhypopituitarism.Magnetic resonance imaging demonstrated a 28 × 22 × 30 mm endo-suprasellar mass compressing the optic chiasm.The patient underwent endoscopic transnasal transsphenoidal resection.Histopathological and immunohistochemical examination identified two tumors of distinct histogenesis within the same specimen: a pituitary adenoma and metastatic melanoma.The melanoma component was positive for Melan-A, HMB-45, SOX10, and S-100, confirming melanoma metastasis to the pituitary adenoma and establishing tumor-to-tumor metastasis.Postoperatively, the patient's visual function improved, and he was discharged on postoperative Day 5.This case demonstrates the diagnostic value of thorough histopathological and immunohistochemical evaluation when the clinical behavior of a previously diagnosed sellar lesion changes in a patient with systemic malignancy.Surgical decompression improved visual function and provided a definitive tissue diagnosis, supporting coordinated multidisciplinary management.