SNP Browser for Human [Homo sapiens] Genetic Disorders

DiseaseID	HGD53
Genetic Disorder	Skin Cancer
Gene Name	melanocortin 1 receptor (alpha melanocyte stimulating hormone receptor)
Description	Skin cancer is the most common type of cancer in the United States. An estimated 40 to 50 percent of Americans who live to age 65 will have skin cancer at least once. The most common skin cancer is basal cell carcinoma, which accounts for more than 90 percent of all skin cancers in the United States. The most virulent form of skin cancer is melanoma. In some parts of the world, especially in Western countries, the number of people who develop melanoma is increasing faster than any other cancer. In the United States, for example, the number of new cases of melanoma has more than doubled in the past 20 years. Forms of skin Cancer:- Three types of skin cancer are the most common: Basal cell carcinoma is a slow-growing cancer that seldom spreads to other parts of the body. Basal cells, which are round, form the layer just underneath the epidermis, or outer layer of the skin. Squamous cell carcinoma spreads more often than basal cell carcinoma, but still is considered rare. Squamous cells, which are flat, make up most of the epidermis. Melanoma is the most serious type of skin cancer. It occurs when melanocytes, the pigment cells in the lower part of the epidermis, become malignant, meaning that they start dividing uncontrollably. If melanoma spreads to the lymph nodes it may also reach other parts of the body, such as the liver, lungs or brain. In such cases, the disease is called metastatic melanoma.
Symptoms	The most commonly noticed symptom of skin cancer is a change on the skin, especially a new growth or a sore that doesn't heal. Both basal and squamous cell cancers are found mainly on areas of the skin that are exposed to the sun - the head, face, neck, hands and arms. However, skin cancer can occur anywhere. For melanoma, the first sign often is a change in the size, shape, color or feel of an existing mole. Melanomas can vary greatly in the way they look, but generally show one or more of the "ABCD" features: Their shape may be Asymmetrical. Their Borders may be ragged or otherwise irregular. Their Color may be uneven, with shades of black and brown. Their Diameter may change in size
Causes	Skin cancer begins in your skin's top layer — the epidermis. The epidermis is as thin as a pencil line, and it provides a protective layer of skin cells that your body continually sheds. The epidermis contains three types of cells: Squamous cells lie just below the outer surface. Basal cells, which produce new skin cells, sit beneath the squamous cells. Melanocytes, which produce melanin — the pigment that gives skin its normal color, are located in the lower part of your epidermis. Melanocytes produce more melanin when you're in the sun to help protect the deeper layers of your skin. Extra melanin produces the darker color of tanned skin. Normally, skin cells within the epidermis develop in a controlled and orderly way. In general, healthy new cells push older cells toward the skin's surface, where they die and eventually are sloughed off. This process is controlled by DNA — the genetic material that contains the instructions for every chemical process in your body. Skin cancer occurs when this process malfunctions. When DNA is damaged, changes occur in the instructions, which can cause new cells to grow out of control and form a mass of cancer cells. The role of UV light Much of the damage to DNA in skin cells results from ultraviolet (UV) radiation found in sunlight and in commercial tanning lamps and tanning beds. UV light is divided into three wavelength bands — ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). Only UVA and UVB rays reach the earth. UVC radiation is completely absorbed by atmospheric ozone. At one time scientists believed that only UVB rays played a role in the formation of skin cancer. And UVB light does cause harmful changes in skin cell DNA, including the development of oncogenes — a type of gene that can turn a normal cell into a malignant one. UVB rays are responsible for sunburn and for many basal cell and squamous cell cancers. But UVA also contributes to skin cancer. It penetrates the skin more deeply than UVB does, weakens the skin's immune system and increases the risk of cancer, especially melanoma. Tanning beds deliver high doses of UVA, which makes them especially dangerous. Other factors that may contribute to skin cancer Sun exposure doesn't explain melanomas or other skin cancers that develop on skin not ordinarily exposed to sunlight. Heredity may play a role. Skin cancer can also develop from exposure to toxic chemicals or as a result of radiation treatments
Diagnosis	A person’s ability to recognize the signs of skin cancer and perform regular self-examinations are key to early detection. Any time skin cancer is suspected, the lesion should be examined by a dermatologist. Dermatologists detect skin cancer through a visual examination of the skin and mucous membranes. If malignancy (cancer) is suspected, a biopsy will be performed. This involves numbing the area and removing the lesion, or part of it, for microscopic examination. A biopsy is the only way to definitely tell if skin cancer is present. Since a skin biopsy is generally a quick and simple procedure, it is usually performed in a dermatologist’s office or outpatient setting. The type of biopsy performed depends on the type of skin cancer suspected, where on the body the tumor lies, and the tumor’s size. The different types of biopsy procedures used include: Excisional biopsy – The entire tumor along with a margin of tissue that is not a visible part of the tumor is removed. An excisional biopsy is the preferred method for removing lesions suspected to be melanoma. Incisional biopsy – A portion of the lesion is removed during an incisional biopsy, which is usually performed when the lesion is large. A scalpel; a hollow, circular scalpel-like instrument called a “punch” (punch biopsy); or a razor (shave biopsy) is used to remove the sample. The removed sample is examined under a microscope to determine if cancer cells are present and if so which kind. If an excisional biopsy was performed, the physician examining the sample also should be able to determine how deeply the cancer has penetrated the skin. Frequently, the removed sample is sent to a laboratory to be examined by a dermatopathologist, a medical doctor trained in both dermatology and pathology, who uses this expertise to microscopically examine tissue in order to diagnose skin conditions. Dermatopathologists provide expertise in diagnosing difficult cases. In addition to removing the tumor or part of it, the dermatologist also will ask the patient some questions, which usually include when the lesion first appeared, symptoms, and the patient’s history of sun exposure
Treatment	Melanoma can be cured if it is diagnosed and treated when the tumor has not deeply invaded the skin. However, if a melanoma is not removed in its early stages, cancer cells may grow downward from the skin surface. When a melanoma becomes thick and deep, the disease often spreads to other parts of the body and is difficult to control. Surgery is the standard treatment for melanoma, as well as other skin cancers. However, if the cancer has spread to other parts of the body, doctors may use other treatments, such as chemotherapy, immunotherapy, radiation therapy or a combination of these methods.