Distribution of estrogen receptor subtypes,expression of their variant forms,and clinicopathological characteristics of human colorectal cancer

We examined the expression of estrogen receptor (ER) messenger RNAs (ER-, ER-, and ER- isoforms) in colorectal tumor samples and corresponding normal mucosa, paying particular attention exons 3 and 5 of both ER mRNA subtypes that likely suffer deletions, and may encode proteins that have lost either DNA- or ligand-binding moieties. Then we correlated these findings with the clinicopathological properties of the tumors. Our results demonstrated that in all patients the two ER subtype mRNAs were coexpressed in wild-type form. In 10% of the patients the ER- mRNA was also present as an exon-5-deleted form that encoded any aberrant protein. Immunohistochemical analysis revealed that the ER- protein was present in tumor stroma, but not in infiltrating lymphocytes. ER-1 and ER-2, isoforms of ER-, were up-regulated in malignant tissues, whereas the ER-5 isoform, was found to be equally expressed, at very low levels, in the two tissue compartments. No correlations between ER levels and clinicopathological parameters were found. This suggests that the ER- mRNA levels are independent of the tumor characteristics.