Thymic carcinoma and
thymoma are primary
neoplasms of the anterior mediastinum that can involve the lung and pleura in advanced stages or, in rare instances, occur as primary pleural
tumors. Thus these
tumors may be encountered in thoracic and pleural biopsy specimens. Recognizing the immunohistochemical patterns of
calretinin and other
mesothelioma-related markers in
thymic carcinoma and
thymoma may be helpful in avoiding
confusion with
malignant mesothelioma and pulmonary
carcinoma, both of which are major differential diagnoses in this location. Accordingly, in the present study we examined the expression of
calretinin,
mesothelin,
cytokeratin (CK) 5/6,
thrombomodulin, HBME-1, Wilms' tumor-1 (WT-1), Ber-EP4, MOC-31, BG-8,
B72.3,
carcinoembryonic antigen (CEA), CD15, thyroid transcription factor-1 (TTF-1), p63, and CD5 in 22
thymic carcinomas and 35
thymomas, and compared the results with those of
malignant mesothelioma and pulmonary
adenocarcinoma. Around 1/3 of
thymic carcinomas were positive for
calretinin and/or
mesothelin. Both
thymic carcinomas and
thymomas were frequently positive for CK 5/6. Immunoreactivity for HBME-1 was seen in 4
thymic carcinomas and 10
thymomas. Except for 1
thymic carcinoma being positive for WT-1, all other
thymic carcinomas and
thymomas were negative for WT-1 and
thrombomodulin. None of the
thymic carcinomas and
thymomas expressed TTF-1. More than 70% of the
thymic carcinomas were positive for Ber-EP4, BG-8, and CD15. The positive rates of MOC-31,
B72.3, and CEA in
thymic carcinomas were in the middle between those in
mesothelioma and pulmonary
adenocarcinoma. All thymic epithelial
tumors revealed nuclear immunoreactivity for p63. Nine
thymic carcinomas (41%) expressed CD5. We found that a panel of positive p63, negative
thrombomodulin, WT-1, and TTF-1 is most discriminatory for thymic epithelial
tumors. Other mesothelial (
calretinin and
mesothelin) and epithelial (Ber-EP4, BG-8, and CD15) markers are less contributory in discerning thymic epithelial
tumors due to their overlapping expression with
malignant mesothelioma and pulmonary
adenocarcinoma. Given the complexity of the staining patterns among the different entities, proper immunohistochemical stainings should be selected and interpreted with caution, and correlated with clinicopathologic findings in the differential diagnoses of thoracic biopsy specimens.