Zhao L, Westerhoff M, Hornick JL, et al. - Researchers intended to validate the decreased expression of MFAP5 in colonic tumor stroma using immunohistochemistry and to investigate the utility of MFAP5 as a marker to facilitate diagnosing an invasive component vs pseudoinvasion in colon polyps. While there was intact MFAP5 immunoreactivity in the uninvolved normal connective tissue, there was marked decline of MFAP5 immunoreactivity in the desmoplastic stroma surrounding the invasive component in ll 19 colon cancer resection cases assessed. The variation in MFAP5 expression levels was most marked within the tumor, while a more heterogeneous expression pattern was noted at the tumor invasive front. In the stroma around mucin pools, decrease of MFAP5 staining was also noticed in six out of nine sections from mucinous adenocarcinomas and in areas with high-grade dysplasia. Intact expression of MFAP5 was observed in the stroma surrounding the displaced adenomatous glands in nine out of 12 polyps with pseudoinvasion for the polypectomy cases. In eight of ten malignant polyps, in the stroma surrounding small foci of invasive adenocarcinoma, loss of expression of MFAP5 was observed. In conclusion, MFAP5 is a beneficial marker that may help differentiate normal connective tissue from stroma within invasive colonic adenocarcinoma. Moreover, in colonic adenomatous polyps with a sensitivity of 80% and a specificity of 75%, MFAP5 may facilitate the differentiation between pseudoinvasion and true invasive cancer in this small cohort.