Detection of carbonic anhydrase IX protein in the diagnosis of malignant pleural effusion by enzyme-linked immunosorbent assay and immunocytochemistry.

BACKGROUND

Carbonic anhydrase IX (CAIX) is a hallmark of metabolic change in cancer cells. The aim was to evaluate the utility of CAIX expression for the detection of malignant pleural effusions by enzyme-linked immunosorbent assay (ELISA) and immunocytochemistry.

METHODS

A total of 97 pleural effusions including 54 benign effusions, 10 atypical effusions, and 33 malignant effusions, classified based on cytological diagnosis and etiology, were subjected to ELISA to measure protein level and to immunocytochemistry in cell blocks to determine CAIX expression.

RESULTS

CAIX levels were significantly higher in the malignant group compared with the benign group. Receiver operating characteristic curve analysis of benign and malignant pleural effusion for CAIX indicated an area under the curve of 0.82 with a value of 1882 pg/dL as the best threshold for distinguishing benign from malignant effusions, which yields a sensitivity, specificity, and accuracy of 63.6%, 94.4%, and 82.8%, respectively. None of the benign effusion expressed CAIX by immunocytochemistry. Malignant effusion cell blocks expressed CAIX in 63.6% of cases with 100% specificity. Upon combination of CAIX level and immunocytochemistry to detect malignant pleural effusions, the sensitivity and accuracy increased to 81.8% and 89.7%, respectively. The CAIX level determined by ELISA and the CAIX expression detected by immunocytochemistry were positively correlated. In atypical effusions, 5 cases (50%) exhibited CAIX levels higher than the cutoff value or were highlighted by CAIX immunocytochemistry.

CONCLUSIONS

ELISA and immunocytochemistry methods for determination of CAIX protein are potential additional tests for detection of malignant pleural effusions.