Phenotypic change of muscularis mucosae in early invasive colorectal adenocarcinoma

Background-Invasive colorectal adenocarcinomas have bundles of eosinophilic spindle cells, which are regarded as myofibroblasts, in their desmoplastic stroma, some of which are continuous with the muscularis mucosa. Aim-To investigate the relation between the eosinophilic spindle cells and the muscularis mucosa based on their cytoskeletal phenotypes in early invas ive colorectal adenocarcinoma. Methods-Formalin fixed, paraffin wax embedded tissues of 17 early invasive colorectal adenocarcinomas were immunostained for alpha -smooth muscle acti n (alpha -SMA), desmin, and vimentin. Results-The phenotype of the muscularis mucosa was alpha -SMA positive, des min positive, and vimentin weakly positive, whereas the eosinophilic spindl e cells showed a decreased degree of immunoreactivity for alpha -SMA and de smin in particular, and an increased degree of immunoreactivity for vimenti n. The degree of phenotypic difference between the muscularis mucosa and th e eosinophilic spindle cells was greater in the eosinophilic spindle cells in the centre of the invasive area that were not continuous with the muscul aris mucosa than ire the eosinophilic spindle cells continuous with the mus cularis mucosa. Conclusions-These findings suggest that the smooth muscle cells of the musc ularis mucosa change their phenotype to become eosinophilic spindle cells, namely myofibroblasts, in the early invasive area of colorectal adenocarcin oma.