Invasive carcinomas may arise in colorectal adenomas with high-grade dysplasia and with carcinoma in situ.

Colorectal carcinomas (CRC) usually arise in colorectal adenomas (CRA) displaying high-grade dysplasia (HGD) or carcinoma in situ (CIS). The aim was to assess the frequency of adenomas displaying HGD or CIS in a cohort of consecutive CRA with submucosal invasive carcinoma. Ninety-two consecutive adenomas were investigated. Sub-mucosal invasion was present in the 39 adenomas with HGD (42%) and in 58% (53/92) of the adenomas with CIS (p<0.05). Sections from 49 adenomas were stained with the DNA-specific Feulgen reaction and for the proliferation marker Ki-67. Five consecutive high power fields (HPFs) were evaluated using a x40 objective. Marked Feulgen reaction was recorded in 91.8% or in 101 of the 110 HPFs studied in adenomas with HGD, but in none of the 135 HPFs studied in adenomas with CIS (p<0.05). Intense Ki-67 expression (>/=75%) was present in 98.2% or in 108 of the 110 HPFs studied in adenomas with HGD, but only in 1.4% or in 2 of the 135 HPFs in adenomas with CIS (p<0.05). Hence, HGD cells and CIS cells can be differentiated not only morphologically but also chemically by the semi-quantitative appreciation of their DNA content and immunohistochemically by the apparent difference in cell proliferation. Although submucosal invasion occurred significantly more frequently in adenomas with CIS than in those with HGD, as many as 42% of the adenomas with submucosal invasion displayed HGD at histology. Despite morphological, chemical and immunohistochemical dissimilarities, these 2 non-invasive neoplasias might have similar biological behaviour in terms of progression towards submucosal invasion.