Mixed hyperplastic - adenomatous polyps (serrated adenomas). An intermediate step in colorectal carcinogenesis?

We compared clinicopathological characteristics of colorectal polyps, in order to investigate the hypothesis of neoplastic transformation of hyperplastic polyps. Of 4723 colonoscopies performed in our department over four years, 22 patients with 23 mixed hyperplastic polyps (MHAP) were found. These were compared with 61 patients with 86 hyperplastic polyps, 40 with 58 tubular adenomas and 27 with 35 villous adenomas. The patients of comparison groups had exclusively one histological type of polyp. A total of 22 synchronous polypoid lesions were found in patients with MHAP; 14 hyperplastic polyps, 6 adenomas and 2 carcinomas. There was a remarkable similarity in the distribution of the four histological types in the colonic regions. The mean age of patients with hyperplastic polyps was 53.7 years, with MHAP 63.2 years (p=0.0093), with tubular adenomas 65.2 years and villous adenomas 69.5 years. Considering the size, 87.2% of hyperplastic polyps were less than 5 mm, while the same was true for 17.4% of MHAP, 50% of tubular and 2.9% of villous adenomas. Larger than 10 mm were 3.5%, 56.5%, 24.1% and 37.1% of the polyps respectively. There was a significant difference (p<0.0001) between MHAP and hyperplastic polyps in the size classifications. In conclusion, the findings of this study further confirm the hypothesis of a neoplastic transformation of hyperplastic polyps. However, the relationship between hyperplastic polyps and the subsequent development of adenomas and carcinomas remains controversial and further larger studies are warranted to evaluate the proposed hyperplastic polyp mixed hyperplastic adenomatous polyp adenoma sequence.