Cancer

There are many kinds of cancers of the foot. Some of the more common are:

Malignant melanoma
Although this makes up only 1% of skin cancers, it for over 60% of skin cancer deaths. However, it is curable if caught early. Approximately 30% of melanomas occur in the lower limbs, and 3% percent occur in the feet. 

Neoplastic disorders
Usually called tumours, these are the result of abnormal growth of tissue. Both benign or malignant tumours occur in the foot.

Osteochondromas
Osteochondromas are benign bone tumours under the toenail. Unless they cause irritation to the surrounding tissue, they are generally not very painful. Sometimes, they can deform the toenail and cause an ingrown toenail. Treatment varies, though in rare cases, they need to be removed surgically.

Plantar fibromas
These are a benign tissue tumour or growth on the bottom surface of the foot. Unlike warts, which grow on the skin, these grow deep inside on a thick fibrous band called the plantar fascia. There are a number of nonsurgical measures for treating plantar fibromas, such as orthotics. When these measures fail to provide adequate relief of symptoms, a surgical approach may be necessary.

Giant cell tumours
Benign tumours generally found on the toes, top of the foot, or sides of the foot. They can also occur deep inside the foot. They are firm, irregular masses that are typically painful.