cock's peculiar tumour cock's peculiar tumour cock's peculiar tumour is a sebaceous cyst linked growth that can resemble a squamous cell carcinoma. the name is given after a 19th-century english surgeon edward cock. the proliferating cyst is usually solitary, but it often arises from a simple trichilemmal cysts in the hair follicle epithelium and these are multiple in 70% of cases. they are most commonly found on the scalp where the proliferating trichilemmal cyst will grow to a large size and ulcerate. chronic inflammation can cause the cyst to take the form of a granuloma. this granuloma mimics a squamous-cell carcinoma (both clinically and histologically) and these ulcerating solitary cysts are called cock's peculiar tumour. cock's peculiar tumourspecialtyoncology chronic inflammation causes the cyst to take the form of a granuloma. this granuloma mimics a squamous cell tumour. the most common sites are the ones where one can find hairs. these are, scalp and scrotum.