Melanoma (cancer of pigmented tissue such as moles and one of the most serious forms with respect to fatal outcome) is the least common form of skin cancer. The cancer is usually detected on the skin, about 70% of the time on normal skin and about 30% of the time arising from an existing mole with a sudden change in its colour or size or associated with itching, bleeding, crusting over or swelling. One mole in 200,000 becomes cancerous. Not all melanomas grow quickly, and some may take many years or even decades, hence their greater appearance in older people.
The usual treatment is surgical excision, and the survival rate is 95% if diagnosis is early. The prognosis is worse for those with large lesions, since the disease is more easily able to spread to other organs.
There are four kinds of melanoma: (a) superficial spreading melanoma, a small lesion with irregular borders and red, white, blue or blue-black spots on the trunk or the limbs, occurring in about 70% of cases irrespective of age; (b) nodular melanoma, typically a shiny, firm pearl to black bump or lesion anywhere on the skin and comprising roughly 15% of cases, usually in people between the ages of 20 and 60; (c) acral lentinginous melanoma, being a dark lesion on the palms, soles, tips of fingers and toes or mucous membranes, occurring in about 10% of cases and more common in old age; (d) lentigo maligna melanoma, which is a large brownish spot with darkish speckles, especially on skin overexposed to sun and occurring in about 5% of case, frequently in the elderly. Melanomas can also be found on eye tissue.
There is some circumstantial evidence that UV light "causes" melanoma, but there is little understanding of the precise mechanisms of initiation, promotion, biologically effective dose, or what happens in the period between exposure and development of melanoma. Both UVA and UVB cause sunburn, but UVB initiates the production of Vitamin D3, which is protective of skin and may inhibit the development of skin lesions.
There does not appear to be much mutation-related evidence in the incidence of the disease (unlike other skin cancers). In particular, exposure to ultra-violet light is not transparently related to melanoma; melanomas rarely occur on face and hands, which skin is most exposed to the sun; they occur in ocular tissue that the sun cannot reach; and farmers are not especially prone to melanomas.
This stands in stark contrast to the well-established findings tying sun exposure to the less deadly skin cancers, the basal and squamous cell carcinomas. The risk to fair-skinned people is not necessarily above average, although those who tan easily are at a lower-than-average risk. A recent American study found no protection afforded by sunscreens against melanoma. The scientists warn that the use of sunscreens could actually increase the incidence of melanoma by encouraging prolonged exposure to UV radiation.
Melanoma is the fifth most prevalent cancer. Rates of melanoma have been rising since the 1990s, surprisingly more among indoor workers. One person dies from malignant melanoma every hour and a person's lifetime risk of developing melanoma is one in 75.
The oldest tumour registry in the USA traces the increase back to 1934 and shows a doubling of the rate every 10 to 12 years. This may be as much due to early detection as incidence. The incidence of melanoma in American blacks has remained fairly stable and below 1 per 100,000. In white people in the USA, there has been a steady increase from 6 cases per 100,000 in 1973 to around 12 per 100,000 between 1986 and 1990 -- an annual growth rate pf 4% growth each year. In 2001, the growth rate was estimated at 4.3%, amounting to approximately 32,000 new cases of melanoma each year. The death rate from melanomas increased by 40% in women and by about 110% in men since 1960 in the USA.
Australia has the highest incidence of melanoma in the world: 35 to 40 new cases annually for every 100,000 people. Among Asians, the incidence is low: 0.4 per 100,000 people in Japan. Two out of five Australians will develop skin cancer during their lives. Melanoma is the fifth most common cancer in South Australia and worldwide has been increasing over recent decades by 3 to 7% per year. Between 1980 and 1986, there was a 50% rise in malignant melanomas in the UK (1,827 cases in 1980 and 2,635 in 1986). The more common, though seldom fatal, forms of skin cancer increased from 19,000 to 25,000 over the same period.
Skin cancer is the most common cause of cancer in women between twenty-five and twenty nine.
5 to 10% of melanoma patients have a close family member with the disease. People who have had a melanoma have an increased risk of twofold to tenfold of getting another one. People with large numbers of moles, more than 100, are at increased risk as well.