The nomenclature for sebaceous neoplasms is controversial. Sebaceous carcinomas most commonly occur in the eyelids, where they generally arise from the meibomian glands and the glands of Zeiss. They may also occur almost anywhere in the skin, including ear, foot, penis and labia. Clinically these lesions are often mistaken for chalazions, chronic blepharoconjunctivitis or carbuncles. Sebaceous carcinoma of the eyelid can also invade the orbit and frequently metastasize causing death.
Extraocular tumors can also metastasize but are less likely to cause death.
Keratoacanthoma usually starts as a red papule that rapidly grows to become a skin-colored, shiny nodule with telangiectases and a central horny plug covered by a crust. Frequent sites of involvement include the face and the dorsum of the hands, but they can occur anywhere. The tumors have a tendency to regress, ultimately leaving a scar. The most common visceral neoplasm in MTS is colorectal cancer, occurring in almost half of the patients. The tumors are usually located proximal to the splenic flexure.