Skin cancers are malignant tumors, histologically varied, that develop mostly in the cells of the epidermis, the top layer of the skin (please see below). Skin cancer is a common medical condition throughout the world. According to World Health Organization (WHO), between 2 and 3 million non-melanoma and 132,000 melanoma skin cancer cases are diagnosed globally each year. In the US, it estimated that one in five Americans will have a form of skin cancer in their lifetime according to the American Academy of Dermatology (AAD). For additional information please see skin cancer statistics.
The skin is not just an organ of the human body; it is the largest. It constitutes about sixteen (16%) of our total weight. It is composed of several layers of tissue which work as a protective barrier of the organism against external and environmental aggressions. This is an important organ which also provides other vital functions such as thermal regulation, endocrine function, and sensation.
From a chemical point of view, an average healthy skin comprises of 70% water, 27.5% protein, 2% fat, 0.5% mineral salts and trace elements. In term of cellular structure, the skin consists of three layers of tissue: the epidermis, an epithelial tissue of semipermeable coating which is the outermost layer; the dermis, intermediate layer formed of a connective tissue that supports the epidermis, protects the vascular network and nerve fibers; and hypodermis, the deepest layer made of adipose tissue under the dermis, which crossed by vessels and nerves, coming into the dermis. Cancer usually develops in cells of the epidermis.
Skin cancer is divided into 2 main categories: non-melanoma and melanoma.
Non-melanoma skin cancer is most often diagnosed in Caucasians. It is a tumor of good prognosis; it rarely causes death. Basal cell carcinoma and squamous cell carcinoma are the two most common forms of non-melanomas, accounting for almost all skin cancers. They usually occur in people over 50 years.
Basal cell carcinomas alone are account for about 90% of skin malignant tumors. They are formed in the deepest layer of the epidermis. There are several types of basal cell carcinoma. The most common usually affect the face by causing a lesion of a few millimeters in diameter, flesh-colored or pink, that does not heal. For additional information, please see skin cancer signs and symptoms.
Squamous cell carcinoma is more serious than basal cell but less fetal than melanoma; the tumor has the ability to generate metastases, but this rarely occurs, less than 1% of cases. One of the reasons it can be the fact that most squamous cell skin cancers are detected and treated at an early stage, when the tumor can be easily removed with local treatment methods such as excision or curettage and electrodesiccation. For additional information please see skin cancer treatment.
Melanoma is another form of skin cancer that forms in the melanocytes, the cells that produce melanin (a pigment) and, which are found particularly in the skin and eyes. This tumor tends to progress rapidly and generate metastases. This is the most fetal form of skin cancer, responsible for about 75% of deaths from the disease. Early diagnosis and treatment is required to prevent fetal complications. Once advanced, the tumor will required more drastic therapies. Please see skin cancer treatment options for more information.
Melanoma skin cancer is more than 20 times more common in whites than in African Americans according to the American Cancer Society (ACS). About 73,870 new cases (about 42,670 in men and 31,200 in women) will be diagnosed in the United States in 2015. In Canada, melanoma is the seventh most frequently diagnosed malignant tumor.
Note. Scientists once believed that there could be benign melanomas, well-defined tumors that are not likely to invade the body; and malignant melanomas, please see description above. It is now conventionally known and accepted that all forms of melanoma skin cancer are malignant
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