Basal cell carcinoma arising in a congenital melanocytic naevus in an adult.

Congenital melanocytic naevi (CMN) are common skin lesions. They harbour a risk of malignant transformation, and various lesions have been described as developing within them. A basal cell cancer occurring within a CMN has never previously been described. A case is described of a woman aged 52 years presenting with a slow-growing, symptomatic 3 cm lesion in the centre of a 10×5 cm CMN on her right upper back. Diagnostic core biopsy revealed an ulcerated, infiltrative basal cell carcinoma which was then further excised. The scar has healed with no evidence of local recurrence at 1-year follow-up.