S-100 protein in malignant mesotheliomas.

Recently, the presence of S-100 protein has been described in a few tissues that are not of neuro-ectodermal origin. Here we report the presence of S-100 protein in epithelial and biphasic malignant mesotheliomas and one of seven reactively proliferating mesothelial lesions. Sarcomatous malignant mesotheliomas, six of seven reactive mesothelial lesions and normal mesothelium were without S-100 protein. The presence of S-100 protein in mesothelial cells may indicate intense proliferation.