Introduction and Definition:
Malignant melanoma accounts for 4% of all skin cancers, but it causes 79% of skin cancer deaths. Since 1973 the rate of new diagnosis of malignant melanoma has doubled from six per 100,000 to 12 per 100,000. It is estimated that approximately 50,000 patients will be diagnosed with melanoma this year, and approximately 8000 people will die of the disease. Cancers that metastasize to bone are secondary, meaning that they started elsewhere in the body. Most come from cancers that started in the breast, the prostate, the lung, the kidneys, or the thyroid, and a few from the GI tract such as the stomach and pancreas. Malignant melanoma is not a common cause of cancer metastasis to the skeleton. However, when melanoma does metastasize, one of the most common sites is the skeleton. In the literature, there are very few reports of bone metastasis and bone fracture from malignant melanoma, but they do clearly occur. As of the date of this review, the author has never encountered a case of documented metastasis of malignant melanoma to bone, and has never been called to fix a fracture caused by malignant melanoma.
When skeletal metastasis from malignant melanoma occurs, it is a sign of a very serious stage of the disease. Melanoma is given four stages by the American Joint Committee on Cancer, stage I is Breslow depth of less than 2.01 mm and no ulceration, stage II is Breslow depth of greater than 2.0 mm or lesions at 1.01 - 2.0 mm in depth with ulceration, stage III is regional lymph node metastasis, and stage
IV is distant metastasis, including metastasis to bone.
In patients who die of disseminated malignant melanoma and undergo autopsy, 25 to 50% have metastasis to bone. However, it is the author's opinion that a much smaller number of patients will are alive with metastatice melanoma develop skeletal metastasis that require treatment, such as for pain or for pathologic fracture. It has been found that 80% of bony lesions from malignant melanoma are located in the axial skeleton, the spine, ribs, pelvis, and skull. In summary, the most frequent location of skeletal metastasis on malignant melanoma appears to be the spinal column and the ribs.
Malignant melanoma is one of the most common malignancies of the foot, and it has been reported to metastasize to the adjacent bones in the foot, perhaps by contiguous spread rather then true metastasis. In a similar fashion, subungual (under the fingernail or toenail) melanoma in the hand or the foot has been reported to spread to the adjacent bones of the finger or toe.