Two instances of basal cell epitheliomas and pigmented nevus occurring simultaneously in the same lesion are reported. No explanation other than that of coincidence is offered. However, it is apparent that ulceration or enlargement of a pigmented nevus may be caused by a coexisting basal cell epithelioma. Conversely, the occurrence of pigmentation in basal cell epitheliomas may be due to a coexisting pigmented nevus rather than to symbiotic melanocytes.
Sigal C, Saunders TS. Basal Cell Epithelioma and Nevus PigmentosusTheir Simultaneous Occurrence. Arch Dermatol. 1967;96(5):520-523. doi:10.1001/archderm.1967.01610050042004