Expression and diagnostic implications of carbonic anhydrase IX in several tumours with predominantly clear cell morphology

Aims High expression of carbonic anhydrase IX ( CA IX ) has been reported in clear cell renal cell carcinoma (cc RCC ); few studies have reported CA IX expression in other tumours with predominantly clear cell morphology. The aim of study was to examine the expression and diagnostic implications of CA IX in these latter tumours. Methods and results An immunohistochemical study was performed of 159 tumours with predominantly clear cell morphology. The results showed that, in addition to primary (25/25) and metastatic (10/11) cc RCC , CA IX was also expressed in breast (2/2), pulmonary (3/5) and hepatic (1/4) clear cell carcinoma, urothelial carcinoma with clear cell change (3/6), clear cell meningioma (4/6) and ependymoma (2/3), haemangioblastoma (10/10), and clear cell hidradenoma (5/6). However, while strong and diffuse positivity for CA IX was observed in cc RCC , clear cell breast carcinoma, haemangioblastoma, and clear cell hidradenoma, the other cases showed predominantly focal positivity for CA IX . In particular, CA IX staining was often seen at the periphery of necrotic areas. Conclusions Our results indicate that strong and diffuse CA IX expression may be useful for differentiating cc RCC from several clear cell tumours, with the exception of clear cell breast carcinoma, haemangioblastoma, and clear cell hidradenoma.