Review of numerous articles shows that the interpretation of identical histopathologic and cytopathologic findings varies and that there is a lack of unanimity in terminology. Schiller emphasized this problem in his article of 1947 in which he compared the malignant changes of colonic mucosa with those that occurred in cervical and endometrial mucosa and highlighted similarities in terms applied to different features of malignancy. He concluded that much of the difficulty in comparing statistics published by various authors lies in the fact that different authors use different criteria for diagnosis of malignancy: [41] "Changes which one investigator accepts as sufficient for classification of the case as full-fledged carcinoma are accepted by second pathologist only as evidence of a suspicious case, whereas a third voluntarily or involuntarily overlooks the changes and registers the case as negative."

Myers and Bacon also discussed the inconsistency in terminology and acknowledged that sometimes "colonic adenoma" must be considered a malignant tumor in spite the term adenoma indicating a benign tumor. [42] More confusingly, McElwee and Moore applied the term "malignant adenoma" for those adenomas that showed criteria of malignancy. But in the article published by them in 1951 they did not mention the criteria they used to diagnose "malignant adenoma." [43] It is clear that the use of the term "malignant adenoma" is oxymoron. Adenoma, by definition, is never malignant. It is a benign tumor of glandular cells. A "malignant adenoma" is a contradiction in terms, the correct diagnosis for such a lesion being adenocarcinoma.

Turell emphasized in many articles written by him [8,44–46] how much confusion was produced among pathologists by inconsistent terminology. What follows are some quotations verbatim made by Turell in different articles published by him: "The present chaos of names has clouded our ideas and thoughts. These matters are not only of academic but also of practical import. A complex classification is undesirable and unjustified. Considerable confusion is created by the use of such terms as "malignant adenoma," and "adenocarcinoma grade I" which at the same time are purported to connote a "benign" process. Infrequently, adenoma graded by some pathologists as adenocarcinoma Grade I or II have, upon reexamination of the slides, been regarded as benign by our pathologists.[44] Some authors have introduced new terms in an effort to better describe these new concepts in biologic potential. However such terms as "adenoma malignum, adenocarcinoma grade I- benign, and invasive adenoma," when interpreted in the light of their original word meanings, emerge simply as double talk. How can an adenoma, by definition benign, be malignant? The use of such terms only multiplied our confusion. [8] Much of the current confusion stems from the fact that a considerable part of our present knowledge is based on circumstantial or indirect evidence. The existing ignorance about biologic behavior pattern of the adenoma is of course unavoidable. However, this inevitable cause of confusion has been supplemented by the distinctly avoidable factor of inconsistent nomenclature . . . The opinions of ever our most eminent pathologists often vary concerning a given lesion, for not agree to the precise diagnostic criteria of any one of the three main categories [adenomatous, villous, carcinomatous]. [46]

Turell stated also that identical data could be interpreted very differently and could lead to entirely different conclusions. He believed that such errors in interpretation are extremely common and blamed them to be responsible for much of the confusion concerning the nature of adenomas: "Unfortunately, as already shown, interpretation of the available data is not that simple, and the opinions of our most eminent pathologists often vary . . . It is apparent that histologic interpretation at times depends on the philosophy of the pathologist."[49]

Andreassen, in a very comprehensive study of polyps of colon and rectum, acknowledged that distinction morphologic between carcinoma and adenoma is almost impossible. He stressed as Turell that terminology is inconsistent, confusing and dissimilar, and are not used by all pathologists and are not interpreted in a same manner by surgeons: "The transition between nonmalignant polyps and carcinoma generally is quite abrupt and only rarely is it possible to demonstrate a gradual transition between polyp and carcinoma. However, it is not only histologic criteria of malignancy, that are not uniform, also the nomenclature is confusing, and different authors talk about precancrose, epithelial atypism, malignant adenoma, benign adenoma, precarcinomatous polyps, carcinomatous polyps, focal atypism, focal carcinoma, preinvasive carcinoma, adenocarcinoma grade I, etc." [48]

Atypical changes or "atypia" has been used also in other organs such as cervix, lung, and skin by many pathologists. In the colon the term, without being defined clearly, has been applied to some "strange morphologic changes" that are not seen in "typical adenoma" or that are not consonant with the morphologic character of an adenoma. In 1962, Castleman and Krickstien [49] suggested using the term "adenoma with focal atypicality" for adenomas undergoing malignant changes, but no attempt was made by them to define the term exactly. However, Turell equated this term with "adenoma malignum" [47] which was suggested by McElwee and Moore as carcinoma in situ.

Kjeldsberg and Altshuler reported on women with a large mass in her transverse colon. By conventional microscopy, the mass was a moderately differentiated adenocarcinoma extending to the muscularis propria. Inspection of the entire mucosa of the colon revealed three other plaque-like lesions. Microscopic examination of these showed frankly malignant anaplastic epithelium as a full-thickness change, but restricted to the mucosa. The authors named these changes as "carcinoma in situ" of the colon, nonpolypoid type. [50] They defined carcinoma in situ with these words: "The term carcinoma in situ defines a pathologic entity with well recognized criteria; the cellular changes are confined to the epithelium; they are sharply delineated from adjacent normal epithelium; the cellular changes, as a rule, involve atypicality of all cell layers in the epithelium, and must conform to those of anaplasia. By definition, carcinoma in situ is synonymous with intraepithelial carcinoma."

Although Kjeldsberg and Altshuler named these three plaque-like lesions as "carcinoma in situ nonpolypoid type," they did not make any reference to other types of carcinoma in situ, e.g., "carcinoma in situ polypoid type." It is not clear whether they thought about carcinoma in situ polypoid type or not, but all criteria used by them for describing carcinoma in situ nonpolypoid type were also seen in adenomatous polyps. The very same lesions which were first reported by Kjeldsberg and Altshuler as carcinoma in situ nonpolypoid type now are named "flat adenoma" by some and "severe flat dysplasia" or "de novo adenocarcinoma in situ" by others.