Carcinoma is a category of types of cancer that develop from epithelial cells. Specifically, a carcinoma is cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that arises from cells originating in the endodermal, mesodermal or ectodermal germ layer during embryogenesis. Carcinomas occur when the DNA of a cell is damaged or altered and the cell begins to grow uncontrollably and become malignant. It is from the Greek: καρκίνωμα, Romanized: karkinoma, lit. 'Sore, ulcer, cancer' (itself derived from Karakinos meaning crab). Basal cell carcinoma is the most common type of skin cancer. Cancerous cells develop in the basal cell layer of the skin or the lowest part of the epidermis. Basal cell cancers usually grow slowly, and they rarely spread, or metastasize, to nearby lymph nodes or more distant parts of the body.