The anatomical precursor of colorectal carcinoma

The very common hyperplastic polyp is not a neoplasm and is unrelated to either adenoma or carcinoma. Adenomas, which are only one‐tenth as common, may occur grossly as adenomatous polyps or papillary adenomas. Be they large or small, pedunculated, sessile, or flat, they are true neoplasms—non‐invasive and thought of as benign. Depending on size, and probably related to a sessile mode of growth, in adenomas one may readily observe intramucosal carcinoma and/or „early”︁ invasive cancer. On the other hand, although microscopic examination has been performed on many thousands of minute mucosal lesions (e.g. 5 mm or less), „early”︁ cancer, defined as intramucosal carcinoma with or without microinvasion, does not seem to occur unassociated with adenoma. Since colorectal carcinoma is so common, one should easily find many examples of „early”︁ cancer as defined above if the majority of ordinary adenocarcinomas arose directly from normal crypts of Lieberkühn. (Of course the unusual anaplastic undifferentiated colonic cancers or carcinomas arising in ulcerative colitis remain in an area of unknown morphogenesis). The apparent non‐existence of small foci of intramucosal carcinoma, with or without micro‐invasion, in normal mucosa, and their frequency in adenomas, are two fundamental pathologic facts. They seem to disprove the proposition that cancer cells ordinarily arise de novo from the normal cells of the crypt of Lieberkühn without the interposition of a stage in the neoplastic process that we recognize as adenoma.