Adenocarcinomas are a type of cancer that originates in the glandular cells of the epithelial tissue. These cells are responsible for secreting various substances such as mucus, digestive juices, and other fluids. Adenocarcinomas can occur in different parts of the body, including the lungs, colon, breast, pancreas, and prostate. They are among the most common forms of cancer and can be aggressive if not detected and treated early.