Malignant melanoma may also form under the nails of the feet. The thumb and big toe are more commonly affected than the other nails. Often the adjacent skin to the nail is ulcerated.

A condition called Actinic Keratosis is another cancer-causing lesion that can occur on the feet. It is most commonly found in sun-exposed areas of the body such as the foot. On the foot they are frequently mistaken for plantar warts. Treatment consists of freezing the lesions with liquid nitrogen or sharp excision.

Karposi's Sarcoma is another cancerous lesion that can occur on the soles of the feet. They are irregular in shape and have a purplish, reddish or bluish black appearance. They tend to spread and form large plaques or become nodular. The nodular lesions have a firm rubbery appearance. The disease is usually associated with AIDS infection. It can occur without an AIDS infection, but this is very rare.