CALRETININ - A NOVEL IMMUNOCYTOCHEMICAL MARKER FOR MESOTHELIOMA

Immunohistochemistry is a powerful diagnostic adjunct in the different ial diagnosis between malignant mesothelioma (especially of the epithe lial type) and adenocarcinoma metastatic to the serous membranes. Most of the immunological probes commonly used, however, recognize antigen s expressed by the epithelial malignancies and absent from mesothelial cells and mesotheliomas. Probes suitable for the positive identificat ion of mesotheliomas are comparatively scarce and much less commonly u sed because of their reduced sensitivity and specificity, their unsuit ability for staining routinely fixed and embedded tissues, or their la ck of commercial availability. We now document that two different poly clonal antisera to calretinin consistently immunostain mesothelial cel ls and malignant mesotheliomas both in routinely fixed and embedded ti ssue sections and in cytological preparations of serous effusions. The diagnostic sensitivity of this novel immunocytochemical approach reac hed 100%, allowing immunostaining of all 44 mesotheliomas investigated , which included five biphasic and three sarcomatoid types. The specif icity of calretinin immunoreactivity was checked against 294 adenocarc inomas of different origin (19 serosal metastases and 275 primary tumo rs potentially able to metastatize to serosal membranes) relevant for the discussion of the differential diagnosis with malignant mesothelio ma: only 28 cases showed focal immunoreactivity for calretinin. We con clude that calretinin is a most useful marker for the positive identif ication of malignant mesotheliomas.