Carbonic anhydrase IX as a specific biomarker for clear cell renal cell carcinoma: comparative study of Western blot and immunohistochemistry and implications for diagnosis.

Objective: This study aimed to evaluate the usefulness of carbonic anhydrase IX (CA-IX) expression in clear cell renal cell carcinoma (CCRCC) using two different techniques to detect protein expression.

Material and methods: An experimental, cross-sectional, analytical study was conducted to analyse proteins in renal tumour and healthy tissue specimens from 38 consecutive patients who underwent nephrectomy for renal cancer. CA-IX protein expression was measured by immunohistochemistry and Western blot analysis and quantified. Statistical analysis was performed with the positive and negative specific agreements and kappa coefficient. The sensitivity and specificity of both techniques were assessed. Statistical tests were conducted to analyse the association between CA-IX expression quantitation and normal prognosis factors (TNM stage and Fuhrman nuclear grade), only in CCRCC.

Results: The mean patient age was 65 years, 78.9% of patients were men and 57.9% of tumours were CCRCC. CA-IX protein expression was positive in 63.2% of tumours by immunohistochemistry and in 60.5% by Western blot. Both techniques detected CA-IX expression only in CCRCC and unclassifiable tumours. High concordance indices were observed for CCRCC diagnosis. Western blot and immunohistochemistry had a sensitivity of 95.5% and 100%, respectively; the specificity was 100% in both techniques. CA-IX expression quantitation did not correlate with tumour stage or Fuhrman nuclear grade.

Conclusions: Immunochemistry and Western blot techniques can be used to detect abnormal CA-IX protein expression in CCRCC and to support morphology-based diagnostic techniques.