melanoma The most dangerous form of skin cancer, a malignancy of melanocytes, the cells that produce pigment in the skin. Melanoma is most common in people with fair skin, but it can occur in people with all skin colors. Most melanomas present as dark, mole-like spots that spread and, unlike moles, have irregular borders. The…
melanoma, acral-lentiginous A type of malignant melanoma that is uncommon in white people but the most common type in nonwhite people. Acral-lentiginous melanoma starts as an irregular enlarging black flat spot (macule), most often on the palm of the hand and the sole of the foot, less often on a mucosal surface, such as the…
melanoma, amelanotic A colorless melanoma that is detectable only on close examination of the skin.
melanoma, choroidal See melanoma, ocular.
melanoma, lentigo maligna One of the four clinical types of malignant melanoma and the slowest growing type. Lentigo maligna melanoma typically begins as a patch of mottled pigmentation that is dark brown, tan, or black on sun-exposed skin, such as on the face.
melanoma, nodular One of the four clinical types of malignant melanoma, which typically presents as a raised, distinct, bluish-black tumor that may be encircled by particularly pale skin, most often in middle-aged or older adults.
melanoma, ocular A rare type of malignant melanoma that arises from a structure within the eye. The most common sites for ocular melanoma are the choroid, the ciliary body, and the iris. The tumor may metastasize (spread), most often to the liver. Ocular melanoma tends to occur after age 40.
melanoma, superficial spreading One of the four clinical types of malignant melanoma, the most common type in white people, which typically presents as a raised, irregular, colored area that starts in a mole-like shape and spreads across the skin.
Melanosis coli is a benign, reversible condition characterized by brown-to-black discoloration of the large intestine’s mucosal lining due to lipofuscin pigment deposition in the lamina propria. Causes It arises primarily from long-term use of anthraquinone laxatives like senna or aloe, which damage colon cells, leading to apoptosis and macrophage uptake of lipofuscin (not true melanin,…
MELAS syndrome Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome, a rare form of dementia caused by mutations in the genetic material (DNA) in the mitochondria. Most DNA is in the chromosomes in the cell nucleus, but another important cell structure that carries DNA is the mitochondrion. Much of the DNA in the mitochondrion is…
melasma Pigmentation of the cheeks of the face (malar area). When it occurs during pregnancy it is referred to as chloasma or the mask of pregnancy. Melasma darkens with sun exposure.
melatonin A hormone that is produced by the pineal gland and is intimately involved in regulating the sleeping and waking cycles, among other processes. Some people who have chronic insomnia use melatonin supplements. However, melatonin is not recommended for all patients with sleep problems, so one should consult a physician before taking it.