EXPRESSION OF MUSCLE ACTINS IN DIFFUSE MESOTHELIOMAS

Ultrastructural examinations have shown myofibroblastoid differentiati on in sarcomatoid/desmoplastic mesotheliomas, but immunohistochemical expression of muscle actins seldom has been documented, We examined 10 sarcomatoid, 12 epithelial, and five biphasic mesotheliomas immunohis tochemically for the expression of muscle-specific actin (MSA) and smo oth muscle actin (SMA) and compared it with that in 12 specimens of lu ng cancer, Ah of the sarcomatoid mesotheliomas were found to be positi ve for both MSA and SMA. The epithelial cells in nine epithelial and t wo biphasic mesotheliomas were positive for MSA, but SMA was only posi tive in one epithelial mesothelioma. Conversely, the lung cancers were negative for both MSA and SMA in the epithelial cells, except for one specimen that was weakly positive for MSA. The stromal cells in both the epithelial mesotheliomas and lung cancers were negative for cytoke ratin but were positive for MSA and SMA, whereas the sarcomatoid and b iphasic mesothelioma spindle cells were positive for all three antibod ies. We concluded that sarcomatoid mesothelioma was positive for MSA a nd SMA, which is in support of its myofibroblastic differentiation, an d that positivity for MSA in some epithelial mesotheliomas might be of diagnostic value in differentiation from lung cancers. Copyright (C) 1995 by W.B, Saunders Company