Doctor's Notes on Melanoma
Melanoma is primarily a type of skin cancer that affects melanocytes, the cells that produce the pigment melanin. Melanocytes can also be found in the mucous membranes, eyes, adrenal glands, and the brain. Melanoma frequently spreads to distant sites (metastasize) and it is the single most common cause of death from any skin disease.
Symptoms of melanoma include changes in pigmented skin lesions that can be remembered by the ABCDE’s: Asymmetry, Border irregularity, Color multiplicity, Diameter greater than ¼ inch, and Evolution (change) in the size and/or shape. Other symptoms of melanoma may include local bleeding, itching, or burning sensation. When melanoma spreads (metastasizes) to the brain it may cause headaches and seizures. Melanoma that has spread to the lungs can cause shortness of breath and feeling unwell (malaise). Melanoma that spreads to the bones causes bone pain and fractures.
Melanomas most often arise on normal skin, but they may also occasionally occur in conjunction with a benign nevus (beauty mark or birthmark). The identification of potentially malignant pigmented lesions is best remembered by using the first five letters of the alphabet as follows:
- A for asymmetry
- B for border irregularity
- C for color multiplicity
- D for diameter greater than ¼ inch
- E for evolution (change) in the size and/or shape
Melanomas may ulcerate and bleed and occasionally cause these lesions to itch or burn. In summary, melanomas are most often pigmented, asymmetric with respect to color and shape, and tend to enlarge or change over time. The presence or absence of hair follicles is of no significance. The appearance of these cancers has resulted in a number of terms that are somewhat confusing and have limited clinical significance. They include superficial spreading melanoma, nodular melanoma, melanoma in situ, acro-lentiginous melanoma, and lentigo maligna melanoma.
Metastatic melanoma produces effects depending on the affected organ. In the brain, it can cause headaches and seizures. In the lungs, it causes shortness of breath and malaise. In the bones, it causes bone pain and fractures. It can affect any area of the body. Although rare, melanomas can arise in tissue other than skin at any site that contains melanocytes. This includes the eye (uveal melanomas), mucosa (genital or oral tissues), and in the brain.
Like most cancers, the cause of melanoma involves interplay between genetic and environmental factors. It is generally agreed that ultraviolet-light-induced mutations in melanocytes is the single most important environmental factor in the induction of cutaneous melanomas. The fact that these cancers are difficult to produce experimentally as well as their appearance in areas of the body in which no light exposure occurs has fueled some controversy as to causation. Melanomas tend to occur on sun-exposed skin in fair-skinned individuals. On the other hand, there is a correlation between exposure to sunlight as defined by the earth's latitude and the incidence of melanoma. For example, melanoma is much more common in sunny areas, such as Arizona, than in Seattle. About 20% of melanomas are produced by heritable genetic mutations. Some of these genes have been identified. The remainder seem to be due to ultraviolet light-induced changes in genes (mutational events).
Sunlight contains ultraviolet light that is harmful to human skin cells. These energetic light waves can produce mutations in the DNA of skin cells, which in turn can lead to skin cancer. In areas close to the equator, the incidence of cutaneous cancers is dramatically higher due to the increase in sun exposure.
The most obvious skin cancer warning sign is the development of a persistent bump or spot in an area of sun-damaged skin. These spots are likely to bleed with minimal trauma and produce a superficial erosion.
Ultraviolet Light and Skin Cancer
Ultraviolet rays are classified by three types: UVA, UVB, and UVC. UVC is very dangerous, but it does not reach the earth’s surface due to the ozone layer. Exposure to both UVA and UVB radiation poses potential skin cancer risks.
UVA light is the most abundant source of solar radiation. Scientists think it can penetrate the top layer of skin, potentially damaging connective tissue and causing skin cancer. An estimated 50% of UVA exposure occurs in the shade. Light skin is far more vulnerable to UVA radiation: while dark skin allows only 17.5% of UVA to penetrate, light skin allows 55% of UVA light to pass through.
Sunburns are mostly caused by UVB radiation. Because of the ozone layer, UVB light accounts for only about 5% of the light that reaches the earth’s surface. UVB light can be filtered out by glass windows and does not penetrate as far into the skin as UVA, but it can still cause some forms of skin cancer. UVB is absorbed directly by DNA. Dark skin is twice as effective as light skin at protecting against UVB penetration.
How Skin Cancer Develops
UV light causes skin cancer by damaging the skin’s cellular DNA. That damage is caused by free radicals, which are hyperactive molecules found in UV light. Free radicals cause damage to the DNA double helix, changing the way cells replicate and naturally die, which is how cancer develops. In addition to sun exposure, free radicals are also found in environmental pollutants, cigarette smoke, alcohol, and other toxins.
Melanoma (Skin Cancer) : Symptoms & Signs QuizQuestion
Self-examination is important in the detection of skin cancer.See Answer
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.