IMMUNOHISTOCHEMICAL STUDY OF RETINOBLASTOMA GENE-EXPRESSION IN COLORECTAL CARCINOMAS

The expression of the retinoblastoma gene (Rb-1) in colorectal carcino mas was studied by Western blotting and immunohistochemistry. Western blot analysis using monoclonal antibodies raised against synthetic pep tides of the Rb-1 gene product (pRB) revealed that colorectal carcinom as overexpressed pRB with a molecular weight of around 110 kD when com pared to normal mucosa. Immunohistochemical staining of formalin-fixed , paraffin-embedded tissue sections from 48 colorectal carcinomas demo nstrated that pRB expression was exclusively localized to the nucleus. More than 50% of the carcinoma cells expressed nuclear pRB in 14 tumo rs (29.2%), while 10-50% of the carcinoma cells did so in 21 tumors (4 3.8%), and less than 10% of cells did so in 13 tumors (27.1%). Althoug h there was no clear correlation between pRB expression and clinico-pa thologic parameters such as tumor stage, tumor size, depth of invasion , and lymph node metastasis, a higher incidence of pRB expression was observed in well to moderately differentiated adenocarcinoma than in t he signet ring cell carcinoma. Thus the present study demonstrated for the first time that the oncosuppressor gene, Rb-1, is overexpressed a t the protein level in most colorectal carcinomas.