Basal cell carcinoma arising from an epidermoid cyst: A hist
Epidermoid or infundibular cysts are the most frequent type of cutaneous cysts. Though typically benign, malignant transformation in epidermoid cysts has been exceptionally reported.

A 42-year-old woman presented with an asymptomatic swelling on the right shoulder since 15 years. She noticed a gradual increase in the size of the lesion in the last one year.
Cutaneous examination revealed a skin-colored to erythematous, firm, nontender nodule of size 2 × 2 cm on the right shoulder.

The nodule was completely excised and sent for histopathological examination with a provisional diagnosis of an epidermoid cyst. The resected specimen showed a cyst in the deep dermis, lined by a 4–5 cell thick layer of epidermal cells with thin granular layer and the lumen-containing proteinaceous fluid. The cyst lining showed a gradual increase in the thickness, with transformation into nests of basaloid cells showing peripheral palisading and peritumoral clefting.

Many mitotic figures were also noted. Melanin pigment was present within the tumor cells and in the stroma. There was no extension of the tumor into the subcutaneous fat. The resected margins were free of malignant cells.

Based on the histopathological findings, a diagnosis of pigmented nodular basal cell carcinoma arising from the wall of an epidermoid cyst was made. There has been no recurrence of the cyst or tumor after 1.5 years of follow up.