Epithelioma cuniculatum pedis, a variant of squamous cell carcinoma.

The rare lesion of epithelioma cuniculatum pedis may be recognized by the gross appearance of a slow-growing, bulky, "squashy," non-healing, exophytic mass of long duration on the sole, exuding foul-smelling purulent keratin debris from numerous sinuses, and biopsies showing extensive infiltrating plaques of keratinizing, well-formed, squamous epithelium forming walls for numerous sinuses filled with purulent material. The rarity of the lesion, the slow growth, and biopsies showing relatively benign-appearing well-differentiated squamous epithelium caused considerable diagnostic difficulty to clinicians and pathologists. The tumor failed to heal, extensively penetrated the soft tissues, ultimately destroyed the metatarsal bones, and invaded the skin of the dorsum of the fott. The lesion should be treated as a slow-growing, well-differentiated squamous cell carcinoma by wide local excision or by amputation when extensive growth causes deformity of the foot or penetration of the metatarsal bones.