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Skin cancer is the most commonly diagnosed form of cancer in humans. [11] [12] [13] There are three main types of skin cancers: basal-cell skin cancer (BCC), squamous-cell skin cancer (SCC) and melanoma. [1] The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer (NMSC).
Cancer can be considered a very large and exceptionally heterogeneous family of malignant diseases, with squamous-cell carcinomas comprising one of the largest subsets. [ 19 ] [ 20 ] [ 21 ] All SCC lesions are thought to begin via the repeated, uncontrolled division of cancer stem cells of epithelial lineage or characteristics.
This way the radiation source can be applied to complex locations and minimize radiation to healthy tissue. [57] After removal of the cancer, closure of the skin for patients with a decreased amount of skin laxity involves a split-thickness skin graft. A donor site is chosen and enough skin is removed so that the donor site can heal on its own.
The enzyme telomerase is used to extend the cancer cell's life span. While the telomeres of most cells shorten after each division, eventually causing the cell to die, telomerase extends the cell's telomeres. This is a major reason that cancer cells can accumulate over time, creating tumors.
Prolonged exposure to ultraviolet radiation from the sun can lead to melanoma and other skin malignancies. [40] Clear evidence establishes ultraviolet radiation, especially the non-ionizing medium wave UVB, as the cause of most non-melanoma skin cancers, which are the most common forms of cancer in the world. [40]
In many developing countries cancer incidence, insofar as this can be measured, appears much lower, most likely because of the higher death rates due to infectious disease or injury. With the increased control over malaria and tuberculosis in some Third World countries, incidence of cancer is expected to rise.
The dispersed tumors are called metastatic tumors, while the original is called the primary tumor. Almost all cancers can metastasize. [39] Most cancer deaths are due to cancer that has metastasized. [40] Metastasis is common in the late stages of cancer and it can occur via the blood or the lymphatic system or both. The typical steps in ...
The central role of DNA damage and epigenetic defects in DNA repair genes in carcinogenesis. DNA damage is considered to be the primary cause of cancer. [17] More than 60,000 new naturally-occurring instances of DNA damage arise, on average, per human cell, per day, due to endogenous cellular processes (see article DNA damage (naturally occurring)).