The most common type of cancer in humans is carcinoma. Carcinoma is a cancer that begins in tissue that lines the inner or outer surfaces of the body. Generally, carcinoma arises from cells originating in the endodermal or ectodermal germ layer during embryogenesis. Specifically, carcinoma is tumor tissue derived from putative epithelial cells whose genome has become altered or damaged, causing the cells to transform and show abnormal malignant properties.
Malignant tumors made up of transformed cells whose origin or developmental lineage is unknown but have specific molecular, cellular and histological characteristics typical of epithelial cells are also characterized as carcinoma.