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How does melanoma spread and how is the treatment when it spreads?



Dear Anthony,

Melanoma is a cancer that begins in the melanocytes.

Melanoma arises from melanocytes, which are cells located in the upper layer of the skin that are responsible for producing pigment (skin color). Most melanomas are dark in color (black/brown) because they contain pigment; however, some melanomas do not contain pigment (amelanotic malignant melanoma) and are difficult to diagnose.

Melanoma can almost always be cured in its early stages. But it is likely to spread to other parts of the body if it is not caught early. Melanoma is much less common than basal cell and squamous cell skin cancers, but it is far more serious.

The thicker a melanoma is, the more likely it is to have spread to lymph nodes at the time of diagnosis when melanoma spreads, it spreads to lymph nodes in the region of the tumor first.

Lymph nodes are small, bean-shaped structures that are part of the immune system. They are found throughout the body and are interconnected by lymph channels.

Melanoma tends to spread through lymph channels that drain into lymph nodes in the local area of the primary skin melanoma. Once a pathologist has determined the thickness of the tumor, the next step in pathological staging may involve surgical removal and examination of the local lymph nodes to determine if apparently normal lymph nodes contain melanoma cells.

There is evidence that surgical removal of involved lymph nodes may improve survival.

Melanoma can spread by local extension (through the lymph system, as described above) and/or by the blood to distant sites. Satellite lesions can also occur in the skin adjacent but separate from the primary melanoma.

These are sometimes called in-transit metastases, implying that secondary melanomas have grown in the skin on their way to spreading to local lymph nodes. Any organ can be involved by metastases from malignant melanoma, but the lungs and liver are the most common sites

The majority of patients with spread of melanoma to local lymph nodes cannot be cured with current therapies.

The average survival of patients with melanoma that has spread outside the local area is only 7.5 months, with only 5-10% of patients surviving beyond 5 years.

Melanoma is one of the few cancers that has shown regression without treatment. Spontaneous partial regression can be common, but complete and permanent regression is rare, with only 33 cases being documented in the world's literature. It has been suggested that spontaneous regressions occur because the patient's immune system rejects the cancer. This observation has caused physicians to try treatments with interferons, interleukins, vaccines and other treatments that stimulate the immune system to react against the malignant melanoma.

Prognosis of the disease: When the disease is confined to the site of origin, the greater the thickness or depth of local invasion of the melanoma, the higher the chance of lymph node metastases and the worse the prognosis.

Following surgery, the highest risk of recurrence is within the first two years, but late relapses are not uncommon.

Cure rates are so high with melanoma in situ that there are essentially no outstanding treatment issues.

The standard treatment of stage I melanoma is surgical removal with pathologically confirmed negative margins.

Stage II melanoma has spread to the lower part of the inner layer of skin (dermis), but not into the tissue below the dermis or into nearby lymph nodes.

The surgical treatment of stage II melanoma typically involves a single procedure in which a local excision of the cancer is performed as well as a SLN biopsy.

Stage III melanoma includes cancers of any thickness with tumor spread to regional lymph nodes. The extent or amount of tumor in the lymph nodes is the most important prognostic factor for patients with stage III melanoma.

Standard surgical treatment for patients with stage III melanoma is removal of the primary cancer with up to 2-centimeter (over an inch) margins of the adjacent skin, depending on the thickness of the primary tumor, and removal of all of the regional lymph nodes.

In the stage IV, or metastatic, melanoma patients have cancer that has spread from its site of origin to distant lymph nodes and/or distant sites.

Additional prognostic factors for stage IV melanoma include site of distant metastases and elevated blood enzyme LDH levels. Distant lymph node metastases and lung metastases have a better prognosis than other distant metastases, such as the brain or liver.

DTIC (dacarbazine) is the standard chemotherapy agent for the treatment of metastatic melanoma, with an overall response rate of approximately 15-20%.

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