Contributor: Gordon K. Klintworth
Adenocarcinomas  are classified according to the pattern formed by the cells or the product of the cells. Thus there is papillary adenocarcinoma [adenocarcinoma - papillary], alveolar adenocarcinoma [adenocarcinoma - alveolar], follicular adenocarcinoma [adenocarcinoma - follicular] and mucinous adenocarcinoma [adenocarcinoma - mucinous]. Adenocarcinoma can arise from many tissues including the lung [adenocarcinoma - lung], breast [adenocarcinoma - breast],  thyroid gland [adenocarcinoma - thyroid], stomach [adenocarcinoma - stomach],  colon [adenocarcinoma - colon],  rectum [adenocarcinoma - rectum] and prostate gland [adenocarcinoma - prostate gland]. Adenocarcinoma can arise from several structures in the eye and its adnexa, but when present most represent a metastatic carcinoma and the morphologic type of adenocarcinoma helps in the identification of the primary tumor. Adenocarcinoma can arise on rare occasions from the lacrimal gland [adenocarcinoma - lacrimal gland] and ciliary body [adenocarcinoma - ciliary body]. An extremely useful antibody in distinguishing pulmonary adenocarcinoma from other adenocarcinomas is an antibody to thyroid transcription factor-1, because the expression of  TTF1 is limited to two types of  adenocarcinoma (thyroid adenocarcinoma [adenocarcinoma - thyroid] and lung adenocarcinoma [adenocarcinoma - lung]).