Carcinoma is the most common type of cancer. It begins in the epithelial tissue of the skin, or in the tissue that lines internal organs, such as the liver or kidneys. Carcinomas may spread to other parts of the body, or be confined to the primary location. The disease has various forms, including:Carcinoma in situ: This early-stage cancer is confined to the layer of tissue from which it started, and has not spread to surrounding tissue or other parts of the body. Invasive carcinoma: This is cancer that has spread beyond the primary tissue layer to surrounding tissue. Metastatic carcinoma: This is cancer that has spread throughout the body to other tissues and organs.