All melanomas are associated with an initial tumor, but sometimes the location is difficult to ascertain. Melanoma is mostly found on (and derived from) the skin, but occasionally it can develop in other organ systems, including the eyes, gastrointestinal tract, genitourinary tract, other mucosal sites and the leptomeninges (the membranes surrounding the brain and spinal cord), where some melanocytes (pigment-producing cells) are also present.
There is also a phenomenon called regression, where the body’s immune system gets rid of the melanoma cells at the primary tumor site, so it is no longer easily detectable clinically. This might explain cases of metastatic melanoma with unknown primary tumor, meaning the patient’s melanoma has spread to other parts of the body, even though the original tumor can no longer be detected.
About the Expert:
Stephen Ho, MD, is a board-certified dermatologist practicing in Greenwood Village, Colorado. He is a Fellow of the American Academy of Dermatology and a member of the American Society for Dermatologic Surgery, The Skin Cancer Foundation and the American Society for Laser Medicine & Surgery.