Metastatic Merkel Cell Carcinoma Within a Cortisol-producing Adrenal Adenoma.

A 54-year-old man with hypertension, type 2 diabetes mellitus, and a history of Merkel cell carcinoma (MCC) of the right thigh presented to the emergency department with a 4-day history of right lower-quadrant abdominal pain associated with constipation and decreased appetite. Workup showed a heterogenous 6-cm right adrenal mass with macroscopic fat. Imaging was suggestive of benign pathology. Hormonal workup for the adrenal nodule led to the diagnosis of Cushing syndrome. The patient underwent a right adrenalectomy for Cushing syndrome with pathology revealing a 6.5-cm adrenocortical adenoma harboring a 2-cm, well-circumscribed neuroendocrine tumor consistent with metastatic MCC. Adrenal collision tumors are exceedingly rare. This case describes a collision tumor that has not previously been identified-a cortisol-producing adrenal adenoma and metastatic MCC.