DNA ploidy analysis of pleural mesotheliomas: its usefulness for their distinction from lung adenocarcinomas

The distinction of malignant mesotheliomas from adenocarcinomas with pleural involvement is often difficult, even with electron microscopic and state-of-the-art histochemical and immunologic studies. We evaluated the DNA ploidy and cell cycle of 45 clinically, morphologically, and immunohistochemically well-characterized malignant mesotheliomas to establish their ploidy profile and compared it with that of 41 pulmonary adenocarcinomas. All the cases were mucin negative and had been immunophenotyped with the following monoclonal antibodies: anti-keratin, anti-CEA, anti-Vimentin, anti-HMFG2, Leu M1 (CD15) and B72.3. Single cell suspensions from the paraffin blocks were prepared following Hedley's technique and were analyzed with a Coulter EPICS V flow cytometer. The resulting histograms were interpreted with the Multicycle software program. Five cases were excluded due to their high coefficients of variation. DNA aneuploidy was defined by the presence of more than one G0/G1 peak on the histograms obtained exclusively from the tumor sample. With this criterion, there is a possibility of missing aneuploid cases with a single aneuploid cycling population; however, fixatives and time of fixation produce such a remarkable variation in the fluorochrome uptake that any control, other than normal tissue present in the sample, was rendered unreliable. Five (14%) cases were DNA aneuploid with DNA indexes ranging from 1.2 to 1.9 (mean = 1.5). Three cases had increased S + G2/M values. Of the aneuploid cases, four were epithelial and one sarcomatous. In comparison, aneuploidy was found in 31 (75%) of the lung adenocarcinomas studied (p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)