MALIGNANT MESOTHELIOMA OF THE PLEURA - THE REPRODUCIBILITY OF THE IMMUNOHISTOLOGICAL DIAGNOSIS

The reproducibility of the histopathological diagnosis of pleural mali gnant mesothelioma (MM), after supple menting routine H&E stain by imm unohistochemistry (IH) in 77 cases of original diagnoses of MM, was as sessed by examining interobserver variation between five pathologists. A battery of commercial antibodies (cytokeratins, vimentin, HMFG-2, a nti Leu-M1 [CD15], BerEP4, B72.3 [TAG-72], carcinoembyonic antigen), c onsidered to be useful in enhancing diagnostic accuracy, was used. The number of definitively classified tumors (accepted MM plus rejected M M) increased from 57 on H&E stain to 60 after IH, with 59 (76.6%) case s being accepted as true MM. Based on IH, the chance-adjusted interobs erver agreement was poor (kappa w = 0.29) and lower than that observed on previous H&E alone. The intraobserver agreement for four of the fi ve pathologists was rather good (kappa w = 0.54-0.56). The inter-and i ntraobserver concordance was higher in accepting than excluding the ca ses as MM. A larger number of cases were classified by all reviewers a s mixed or sarcomatous variants after IH. In the interpretation of eac h immunostain, kappa values ranged from 0.19 for B72.3 to 0.62 for HMF G-2, which were respectively the least and the most consistently inter preted immunostains. The information additionally contributed by IH di d not seem to change the pathologists' diagnoses very much in comparis on with those made by routine H&E stain. Until highly specific and sen sitive probes for the positive identification of MM become available, a careful scrutiny of routinely stained preparations still remains the most rewarding component of the diagnostic pathway.