Advanced microtubular colorectal adenomas: a 10-year survey at a single hospital

Colorectal carcinoma, the third most commonly diagnosed type of cancer in Europe and the USA, usually originates from colorectal adenoma (CRA). Three main histological phenotypes of CRA are usually recognized: tubular, villous and traditional serrated (TA, VA and TSA, respectively). In 1997, we reported a novel histological phenotype, the microtubular adenoma (MTA), epitomized by dysplastic epithelium arranged in closed rings (microtubules), with sideways-elongated outgrowth.

The material includes 4,446 CRAs diagnosed at our Department during a 10-year period (2001-2010).

Out of 4,446 CRAs, 68 (1.5%) were MTA; of these, 38 (55.9%) exhibited low-grade dysplasia (LGD), 17 (25.0%), high-grade-dysplasia, two (2.9%) intraepithelial carcinoma and three (4.4%), intramucosal carcinoma. Out of the 68 MTA, 22 (32.3%) were advanced MTA. Submucosal carcinoma (SMC) was present in eight (11.8%) MTAs. Ninety-four per cent (64/68) of the MTAs were left-sided adenomas. In previous work, we found that cell proliferation occurred in the dysplastic microtubules in MTA, initially in the luminal dysplastic epithelium in TA and VA, and initially at the bottom of the serrated dysplastic crypts in TSA.

Due to these distinctive microscopic and cell proliferative attributes, a predominant left-sided location and the absence of serrated configurations, it is submitted that MTA is a specific CRA phenotype, at variance with TA, VA, and TSA. The high frequency of SMC strongly suggests that MTA is an important alternative pathway in colorectal carcinogenesis.