I. Observations on the adenoma as precursor to ordinary large bowel 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, are true neoplasms. 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. Although microscopic examination has been performed on many thousands of minute mucosal lesions (e.g., 5 mm or less), "early" cancer, defined cancer, defined as intramucosal carcinoma with or without microinvasion, does not seem to occur unassociated with adenoma. The apparent nonexistence of small foci of intramucosal carcinoma, with or without microinvasion, in normal mucosa, and their frequency in adenomas, are two fundamental pathologic facts. They seem to disprove the proposition that cancer calls 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.