Superficial spreading melanoma (SSM) is one of two major cancers [SSM and nodular melanoma (NM)] that arise in melanocytes of persons with white skin. It arises most frequently on the upper back and occurs as a moderately slow-growing lesion over a period of years. SSM has a distinctive morphology: a uniformly elevated, flattened lesion (plaque). The pigment variegation of SSM is similar to but often less striking than the variety of color present in most lentigo maligna melanomas. The color display is a mixture of brown, dark brown, blue, black, and red, with slate-gray or gray regions in areas of tumor regression.
In the early stages of growth there is an intraepidermal or "radial growth" phase, during which tumorigenic pigment cells are confined to the epidermis and thus cannot metastasize (called melanoma in situ) or "thin" SSM, in which the tumor cells are confined to the epidermis and upper dermis. This "grace period" of the radial growth phase, with potential for cure, is followed by the invasive "vertical growth" phase, in which malignant cells consist of a tumorigenic nodule that invades the dermis with potential for metastasis.
The pathophysiology of SSM is not yet understood. Certainly, in some considerable number of SSM, sunlight exposure is a factor, and both SSM and NM are related to occasional bursts of recreational sun exposure during a susceptible period (<14 years). About 10% of the 47,000 new melanomas each year occur in highrisk families. The rest of the cases may occur sporadically among persons without a specific genetic risk. Persons at high risk inherit the gene in a mutated form of a normal gene that controls melanocytic proliferation.
Melanoma usually appears first as a flat or slightly raised growth that displays a variety of colors, such as black and brown, or gray, pink, blue, and white. Its edges are poorly outlined and may blur into the surrounding skin. Its shape is often asymmetrical, so that if one could fold it in half, the edges would not meet. The growth may not exhibit any symptoms, or it may bleed, itch, ooze, or feel sore. The sites where growths commonly occur include the trunk, especially the upper back; the lower legs; the head; and the neck.
Melanoma typically originates in the upper layer of the skin but can rapidly penetrate into deeper layers and then spread through the bloodstream or lymphatic system to distant sites in the body. Common areas of metastasis are the lungs, liver, brain, and bone.
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