Unusual case of primary cutaneous signet-ring cell (histocytoid) carcinoma

Abstract Signet-ring cell (histocytoid) carcinoma is a rare and aggressive skin neoplasm that most commonly affects elderly men. It typically originates from the upper or lower eyelid, with bilateral involvement only in rare cases, and results in a diffuse and infiltrative appearance clinically, radiologically, and histologically (the “monocle” sign). It is essential to carry out a full investigation to rule out metastasis from an internal origin.