We appreciate Berg et al. for their study to replicate the findings of our study published in Modern Pathology [1]. They studied MUC4 expression in 6 sarcomatoid meso- theliomas and 13 sarcomatoid carcinomas of the lung and prematurely concluded its low applicability in differentiat- ing sarcomatoid mesothelioma from sarcomatoid carcinoma of the lung. Their study also showed no MUC4 expression in all six cases of sarcomatoid mesothelioma, which is similar to our study. Regarding MUC4 expression in sar- comatoid carcinoma of the lung they found one case with diffuse expression, three cases showing focal expression, and nine cases with no expression. They have not given the detailed histology of their cases of sarcomatoid carcinoma. In our publication, we included and analyzed the MUC4 expression in 5 cases of spindle cell carcinoma, and 24 cases of pleomorphic carcinoma including the sarcomatoid (spindled cells) component. We found no expression of MUC4 in all five pure spindled cell types, but found most of the sarcomatoid component of pleomorphic carcinoma to have focal to diffuse expression. We agree with them to some extent about the staining of MUC4 in sarcomatoid carcinoma, provided if their cases were dominantly pure sarcomatoid type (spindle cell carcinoma). Further study of MUC4 expression in sarcomatoid carcinoma of the lung is needed with more cases of pleomorphic carcinoma with spindled cell components.
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