Matsumoto S, Hamasaki M, Kinoshita Y, et al. - Through virtual microscopy former to immunocytochemistry (ICC) or fluorescence in situ hybridization (FISH), followed by analysis and quantification of their morphological features, malignant pleural mesothelioma (MPM) cells with either BRCA1-associated protein 1 (BAP1) loss identified by ICC or 9p21 homozygous deletion (HD) or discovered by FISH were recognized in order to examine whether MPM cells with BAP1 loss explicated the same morphological features distinguished in MPM cells with 9p21 HD. MPM cells with BAP1 loss or 9p21 HD vs reactive mesothelial cells showed considerably more prevalent cell-in-cell engulfment, multinucleation, and larger multicellular clusters comprised of > 10 cells. Therefore, MPM cells with BAP1 loss or 9p21 HD was observed to share comparable cytological characteristics, intimating that in order to identify MPM cells harboring such genetic aberrations, the same morphological criteria could be used.