Urinary carbonic anhydrase IX splicing messenger RNA variants in urogenital cancers

To identify molecular biomarkers for tumor diagnosis and monitoring of disease progression, several noninvasive tests on liquid biopsy have been proposed for different cancers including those of urogenital origin. Among biomarkers, carbonic anhydrase IX (CAIX) has gained attention as it regulates extracellular pH and induces cytoplasmic alkalization contributing to malignant progression and poor treatment outcome. Works on tissues suggested the potential use of CAIX as a tumor biomarker for urogenital malignancies, but only few studies have been performed on its detection in urine.

The aim of the present study is the measurement of CAIX messenger RNA (mRNA) in urine sediments of patients affected by kidney, prostate, and bladder cancers to evaluate the clinical sensitivity and specificity of the test.

The quantification of the total CAIX mRNA concentration and of its full-length isoform (CAIX FL) have been performed by reverse transcription quantitative polymerase chain reaction (RT-qPCR) on RNA extracted from urine sediments of patients affected by urogenital cancers.

Urinary total CAIX mRNA expression resulted to be lower in patients with kidney and prostate cancer in comparison with the control group, but no statistically significant difference could be evidenced for bladder cancer. The evaluation of the relative percentage of FL isoform mRNA (FL%) showed a significant increase of FL% in urine from patients with cancer (median = 70.8%) in comparison with the healthy subjects (median = 2.6%) and this finding was confirmed for each cancer type separately. The comparison among receiver operating characteristic curves for total CAIX mRNA, CAIX FL mRNA, and FL% indicated that FL% shows the best diagnostic performance with 90% sensitivity and 72% specificity. Comparison of the results obtained in urine with those found in the corresponding tissues indicated 80% concordance.

The CAIX mRNA expression in urine sediments can be considered a surrogate marker of CAIX expression in tumor tissues of urogenital origin. In particular, the analysis of FL% possesses the best characteristics to be a suitable noninvasive biomarker for urogenital cancer diagnosis.