FHIT protein is expressed in benign mesothelium and has no clinical value in detecting carcinoma in body cavity effusions.

The fragile histidine triad (FHIT) protein is a suspected tumor-suppressor gene frequently expressed in adenocarcinomas of the lung and other organs. Its expression in benign mesothelium has not been reported. This study examined the expression of FHIT in mesothelium from benign body cavity effusions. FHIT expression was also examined in a diversity of malignant effusions to evaluate any value of the FHIT protein to discriminate carcinomas from benign mesothelium. Fifty-eight cases of benign and malignant effusions were immunostained using cell block material and two different antigen retrieval methods with the ABC method. Benign and malignant cases were scored for percentage of cells with strong immunoreactivity. Benign mesothelium exhibited strong immunoreactivity for the FHIT protein in 32 of 32 (100%) cases, with 26 of 32 (81%) cases having expression in at least 50% of cells. Seventeen of 21 (81%) cases of adenocarcinomas also exhibited the FHIT protein in at least 50% of tumor cells. FHIT expression was also noted in small numbers of other malignancies. The FHIT protein is expressed consistently in benign mesothelium as well as many types of adenocarcinomas. Immunostaining for this protein has no value in discriminating adenocarcinomas from reactive mesothelium.