Pilomatrical carcinoma is the rare malignant counterpart to benign pilomatricomas, which arise from the base of the hair follicle. It is seen almost exclusively in adults and is more common in males. Both pilomatrical carcinoma and pilomatricoma are associated with CTNNB1 (beta-catenin) mutations and disturbances in the Wnt-signaling pathway.

This section is a shave biopsy of sun-damaged skin containing nodular dermal tumour comprised of islands of poorly-differentiated basaloid cells with prominent areas showing pilomatrical type keratinization with sheets of “ghost cells” as well as atypical single cell keratinization. The tumour shows significant malignant features such as cellular crowding, cytologic atypia, and prominent mitotic activity. Focally there are some squamoid areas but there is no glandular or sebaceous differentiation. The epidermis shows Bowenoid actinic keratosis.

The additional molecular changes responsible for the malignant transformation in pilomatrical carcinoma are unclear. Treatment with wide local excision is typically sufficient for this tumour as it has low metastatic potential, however due to its infiltrating growth pattern, local recurrences are common.