Skin cancers have increased yearly by 5%, and the culprit is thought to be the incresed exposure to ultraviolet sunrays. The bulk of skin cancers are the squamous cell and basal cell types and are distinguished from malignant melanoma and Merkel cell carcinoma by their morphology and cell type of origin. The clinical behavior of the squamous and basal cell skin cancers differ significantly from melanoma since they rarely metastasize. Malignant Melanoma comprise about 10-15% of all skin cancers and depending on the depth of skin invasion, it can travel to other tissues and organs such as the lymph nodes, lung, bones and others. Individuals with 30 or more nevi, family history of melanoma and past history of melanoma have higher risk of deloping the disease. The precursor lesion is often a mole or an atypical nevus. Diagnosis is made first by visual inspection and then by an incisional biopsy for suspected lesions. Size greater than a pencil eraser, dark coloration, irregular borders are a few clues to a transformed nevus. Early diagnosis is often reflected by the findings of thin depth, 1 mm or less, and these thin melanomas the cure rate is excellent.
Individuals with light skin and hair coloration undergoing prolonged exposure to sunrays and ultraviolet rays have increased risks of melanoma. Sunburn with blister formation, and repeated prolonged exposures over years, are contributing factors. Melanoma can also appear in non-sun exposed skin. Since heavy sun exposure often occurs during childhood, parents are advised to pay attention to their children's play habits and encourage reduction in heavy sun exposure. Simple rules are: 1. avoid sun exposure during the mid-day hours (angle of rays penetrate the filtering effect of the atmosphere in a more direct manner), 2. avoid continuous exposure of 2 hours or longer, best to rest under shade between exposures, 3. Keep sun exposures to short periods for few days until natural suntan develops on the child. 4. Always use sunscreen and protective clothing knowing that the protective effect is overcome by prolonged sun exposure.
Individuals with darker coloration are still at risk for melanoma and the primary sites are usually in the acral locations and presenting first as lentiginous type such as ungual (nailbed) melanoma, and melanocytic lesions on palms and soles.
HOW WIDE TO EXCISE A MELANOMA?
Up until a couple of decades ago, the standard treatment was a 5 cm margin resection closed with a skin graft. Acral lentiginous or ungual melanomas were treated with amputation. Today, 2 cm margin is sufficient for melanoma 1 to 4 mm in depth and 1 cm margin for thinner melanomas. Wide resection includes the subcutaneous fat down to the fascia and may include the fascia depending on location and morbidity. Skin graft for closure are rarely applied today.
SENTINEL LYMPH NODE MAPPING AND NODE DISSECTION
The sentinel lymph node mapping and biopsy technique has been popularized by Dr Morton in this disease and the method varies slightly from breast cancer. Both blue dye and radioactive dye are necessary since in most cases the location of sentinel node can vary. The location of the incision for the sentinel biopsy can be determined by the gamma probe which works as a more precise geiger counter. The sentinel nodes location can be determined more easily by visualizing the blue node once the nodal groups are reached below the skin. Lymphocyntigraphy, a picture of the radioactivity distribution, can determine the site for biopsy when multiple drainage groups are encountered. The sentinel can be one to three nodes. If permanent pathology indicate melanoma cells then a full node dissection should be done. Even in cases of micrometastases where few melanoma cells can only be found by special staining techniques, in melanoma in contrast to breast or colorectal cancer, a node dissection should be carried out. Dr Morton is currently conducting an international trial, MSLT III, where the need for node dissection in SLN positive melanoma patients are randomized to completion node dissection or not. The hypothesis is that a completion node dissection will not affect survival rates, however the morbidity of local recurrence may not be fully measured by this trial.