Most skin cancers ride ultraviolet light into DNA
Among cancers that doctors identify in people, skin tumours top the list worldwide, and more than 90 percent of cases link to ultraviolet radiation from the sun or tanning devices. Three main types—basal-cell, squamous-cell, and melanoma—behave very differently once they take hold.
Skin cancers arise when abnormal skin cells invade or spread. Globally they account for at least 40 percent of cancer cases. Nonmelanoma skin cancer alone is estimated at 2–3 million people yearly, though statistics are incomplete; roughly 80 percent of those are basal-cell and 20 percent squamous-cell. Basal-cell tumors grow slowly, often as shiny raised areas with fine vessels or ulcers, damage nearby tissue, yet rarely metastasize or kill. Squamous-cell cancers more often spread and usually look like hard, scaly lumps or ulcers. Melanomas are least common among the three but most aggressive; warning signs include moles changing size, shape, or color, irregular borders, multiple colors, itch, or bleeding.
Ultraviolet exposure raises risk for all three types and has climbed since the industrial revolution, partly with ozone loss. Childhood exposure especially harms melanoma and basal-cell risk; total lifetime dose matters more for squamous-cell disease. Between 20 and 30 percent of melanomas arise from moles. Lighter skin and impaired immunity (medications or HIV/AIDS) increase vulnerability. Tanning beds are another UV source; the World Health Organization places users in its highest skin-cancer risk category. BCC and SCC often carry UVB-signature mutations from direct DNA damage, while melanoma is linked mainly to UVA via free-radical indirect damage. Cells can repair much UV injury by nucleotide excision repair, yet heavy exposure can overwhelm that shield.
Cutting UV exposure and using sunscreen appear to help prevent melanoma and squamous-cell cancer; sunscreen's effect on basal-cell risk is unclear. Nonmelanoma disease is usually curable, typically by surgery, sometimes radiation or topical agents such as fluorouracil. Melanoma care may combine surgery, chemotherapy, radiation, and targeted therapy; when spread is distant, palliative care may focus on quality of life. Melanoma five-year survival exceeds about 86 percent in the UK and 90 percent in the United States. The ABCDE mnemonic—asymmetry, border irregularity, color variegation, diameter over 6 millimeters, evolving—flags melanoma concern. Diagnosis is by biopsy; dermatoscopy can aid basal-cell recognition.
Source: Skin cancer
