GROWING PATTERNS OF COLONIC CANCERS:
ADENOMA CARCINOMA SEQUENCE AND "THE NOVO"

Shigehiro Katakura

Katakura Clinic (Tokyo)

There are difficulties to discuss about the real genesis of colonic cancers: since the genesis of colonic cancers is a problem of cell level, the discussion must be developed on a figure of cells and oncogenetic mutations.

However, as a practical problem, we could not obtain an instrument to distinguish cancers from adenomas. At the moment, it is still important to consider the genesis of colonic cancers by histopathological finding of colonic tumors.
Roughly speaking, two theories of the genesis are proposed. One is adenoma carcinoma sequence, and the other is de novo genesis. Adenoma carcinoma sequence is the theory universally accepted. This theory, originally, means that colon cancers develop in benign adenomas growing over 10mm in size, the cancer grown, occupies and replaces adenoma components. And the cancer invades into submucosal and muscular propria layers. Most of them show polypoid shape. De novo genesis is explained as cancer which can develop without the stage of adenoma. It means that a normal colonic mucosal cell will have genetic mutation and transform into a cancer cell directly. Although, it is fair to say, de novo genesis has not been certified, since no one could find a cancerized single gland in pathological section. Very suspicious lesions have existed, which we can speculate are from the genesis. Though they posses s no adenoma component but only definit cancer in a tumor, they are quite small, below 5mm in size. These lesions showed, mainly, non polypoid figures as superficial depressed types.

It should not be underestimated that adenoma carcinoma sequence is the main route to invaded advanced colon cancers. Under endoscope 85% of polypectomied colon cancers(n=676) possess some of adenoma components. The study which limits the tumor size within a 10mm shows that 80% of cancers also have adenoma components .This means that adenoma carcinoma sequence could occur indipendently of size.

The cancers speculated as de novo genesis, which possess no adenoma components and their size is below 5mm, were recognized as non polypoid figures, especially as the superficial depressed type. Some of them invaded the submucosal layer, though they were rather smaller sizes. It is obvious that they are a minority as original lesions of colon cancers. But one must insist that their invading potential is strong and rapid. We could recognize some polypoid cancers, which have invaded the submucosal layer, and maintain a lower mucosa than a surrounding normal mucosa. These lesions show a possibility that polypoid growth occured with the sub mucosal invasion of cancers, though they were superficial depressed tumors.

The lesions, speculated as de novo genesis and having a growing pattern of size independent of the adenoma carcinoma sequence, could not be a main cause of colon cancers. But they are clinically important and must not be ignored.