KRT5 and malignant epithelioid mesothelioma: A separate analysis of thoracic tumors (mesothelioma vs. squamous cell carcinoma of the lung vs. adenocarcinoma of the lung) revealed that the combined use of both CK5 and CK6 immunostaining hindered the discrimination of these tumors because the positivity rate of lung adenocarcinomas increased from 12.8% (CK5 alone) to 23.7% (CK5 and/or CK6 positive) while both squamous cell carcinomas and epithelioid mesotheliomas were positive in 100% irrespective of whether CK5 alone or CK5 and CK6 were jointly applied (Fig. 3).