Carcinoma occurs as an abnormal cell growth (cancer) develops in the epithelial tissue or cells. The epithelial tissue includes the tissue covering organs or forming the outer layer of these, for example, skin, secretory glands, and part of the tissue covering organs such as lungs or the heart. This implies skin and lungs are part of the epithelial tissue and therefore cancer in these tissues is classified as carcinoma, although there are many other carcinomas such as pancreas cancer or cancer in the mouth.
