Cock's peculiar tumour
Cock's peculiar tumour is a sebaceous cyst linked growth. One form of sebaceous cyst is the trichilemmal cyst; these are thought to arise from the hair follicle epithelium and are most commonly found on the scalp. Usually they are multiple but occasionally there can be a proliferating trichilemmal cyst which grows to a large size and ulcerates. These can resemble a squamous cell carcinoma (both clinically and histologically) and these ulcerating solitary cysts are called Cock's peculiar tumour.
Chronic inflammation causes the cyst to take the form of a granuloma. This granuloma mimics a squamous cell tumour. Hence it is a misnomer. It is not a tumour but looks like a tumour. The most common sites are the ones where one can find hairs. these are, scalp and scrotum.