In previous Parts I and II of this series, we showed, via historical as well as contemporary literature review, that there has been long-standing controversy and confusion among investigators regarding the nature of so-called colonic adenoma. [1,2] In Part III, based on morphologic criteria and histopathologic reassessment, we came to the conclusion that what was long called colonic adenoma or adenomatous polyp is not adenoma, namely, a benign tumor of glandular origin, but carcinoma in situ (CIS), a malignant neoplasm of epithelium that remains confined to that epithelium.[3] Part IV, the last part of the series, via histopathologic comparison between colonic adenoma in one hand and CIS of the skin and of the breast in the other, further reinforces the notion that the so-called colonic adenoma is not adenoma, but is CIS.

In sum and in short, with this series of articles, we emphasize the importance of establishing a correct, precise, and understandable nomenclature that accurately reflects the true nature of lesions. In the colon a lesion that is traditionally and currently named colonic adenoma is not a benign or premalignant one, rather, it is a malignant neoplasm from the outset that is still confined to the mucosa and it should be called CIS. In addition, it is evident that CIS is a unifying concept which can be applied to any epithelium.