The role of adenoma for colorectal cancer development: differences in the distribution of adenoma with low-grade dysplasia, high-grade dysplasia, and cancer that invades the submucosa.

Background: The purpose of this study was to elucidate the role of adenoma in the early stage of colorectal cancer development, we focused on the clinicopathologic relationship between adenoma with low-grade dysplasia (ALGD), adenoma with high-grade dysplasia (AHGD), and cancer that invades the submucosa in the colorectum.

Methods: We clinicopathologically examined a total of 553 adenomas and 58 cancers that invaded the submucosa. The tissues were excised from 479 patients who underwent total colonoscopy.

Results: The percentage of ALGD was 79.9% in the proximal colon, 70.5% in the distal colon, and 48.3% in the rectum, respectively. The percentages of AHGD and cancer were 14.5% and 5.6% in the proximal colon, 21.3% and 8.2% in the distal colon, and 35.4% and 16.3% in the rectum, respectively. In contrast with the distribution of ALGD, the distribution of both AHGD and cancer shifted from the proximal to the distal site, with a statistical significance (P <.01). When the distribution of adenoma was compared according to tumor size, both large- and small-sized AHGD showed a similar cancer distribution, however, both large- and small-sized ALGD showed different distributions.

Conclusion: An important role of AHGD for cancer development in the colorectum may relate to the similar distribution between AHGD and cancer; however, the different distributions observed between ALGD, AHGD, and cancer suggested that ALGD has only a slight association with the development of cancer.