Carcinoma in situ was found in 16.0% of patients with histologically verified cases of solitary and multiple adenomatous polyps of the colon and rectum. In patients with adenomatous polyps only, the incidence was 6.1%. The incidence rose to 47.0% in the group of patients having adenomatous polyps associated with carcinoma in the same segment of the colon. This figure suggests that the diagnosis of carcinoma in situ in a polyp should be followed by careful search for frank adenocarcinoma in the proximity. Organ tissue cultures on the fibrin foam matrix demonstrated a morphological transition from cytologically benign adenomatous polyps into focal carcinoma in situ in more than two thirds of cultured cases. Moreover, a few of these polyps developed invasive features similar to those observed in cultures of colonic adenocarcinoma. The behavior of adenomatous polyps in tissue culture suggests a malignant potential of those lesions and their possible ability to become not only histologic, but also biologic cancers.

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