dermatologic disorders
Melanoma
Classification of Melanoma
There are 4 main types of melanoma and a few minor subtypes. This type accounts for 70% of melanomas. Typically asymptomatic, it occurs most commonly on women’s legs and men’s torsos. The lesion is usually a plaque with irregular, raised, indurated, and tan or brown areas, which often have red, white, black, and blue spots or small, sometimes protuberant blue-black nodules. Small notchlike indentations of the margins may be noted, along with enlargement or color change. Histologically, atypical melanocytes characteristically invade the dermis and epidermis. This type of melanoma most commonly has activating mutations in theBRAFgene at V600. This type accounts for 15 to 30% of melanomas. It may occur anywhere on the body as a dark, protuberant papule or a plaque that varies from pearl to gray to black. Occasionally, a lesion contains little if any pigment or may look like a vascular tumor. Unless it ulcerates, nodular melanoma is asymptomatic, but patients usually seek advice because the lesion enlarges rapidly. This type accounts for 5% of melanomas. It tends to occur in older adults. It arises from lentigo maligna (Hutchinson freckle or malignant melanoma in situ—a frecklelike tan or brown macule). Lentigo maligna usually occurs on the face or other areas of chronic sun exposure as an asymptomatic, flat, tan or brown, irregularly shaped macule or patch with darker brown or black spots scattered irregularly on its surface. In lentigo maligna, both normal and malignant melanocytes are confined to the epidermis. When malignant melanocytes invade the dermis, the lesion is called lentigo maligna melanoma, and the cancer may metastasize. This type of melanoma most commonly has mutations in theC-kitgene. This type accounts for only 2 to 10% of melanomas. Incidence is probably the same regardless of skin pigmentation, but because people with dark skin infrequently develop other forms of melanoma, acral-lentiginous melanoma is the most common type among them. Acral-lentiginous melanoma arises on palmar, plantar, and subungual skin and has a characteristic histologic picture similar to that of lentigo maligna melanoma. This type of melanoma often has mutations in theC-kitgene. Amelanotic melanoma is a type of melanoma that does not produce pigment. It can be any of the 4 main types and is most often grouped with the minor categories of melanoma such as spitzoid melanoma, desmoplastic melanoma, neurotropic melanoma, and others. Accounting for < 10% of melanomas, amelanotic melanomas may be pink, red, or slightly light brown and may have well-defined borders. Their appearance may suggest benign lesions, or a form of nonmelanoma skin cancer, and thereby lead to a late diagnosis and possibly a worse prognosis. 