Onycholemmal carcinoma.

Onycholemmal carcinoma is believed to be of trichilemmal origin, and shows differentiation similar to that found in the trichilemmal portion of the hair follicle. Less then 3 cases are currently in the English literature. All reported cases presented in elderly patients and were without recurrence after amputation. Clinical presentation has been varied and can be very subtle. As with most nail tumors, pain is not a common feature. The diagnosis is based on the histology showing an infiltrative growth of atypical keratinocytes, one or more foci of abrupt keratinization, and usually also keratinous cysts devoid of a granular layer. When a cystic component and clear cells predominate, the subtype description of malignant proliferating onycholemmal cyst has been applied. No standard treatment option or follow up has been established.