ADA and cancer: In the study by Verma et al. (4), the serum lactate dehydrogenase (sLDH)/pleural fluid adenosine deaminase (pfADA) ratio had a high sensitivity and specificity for diagnosing MPE and it was called “cancer ratio (CR).” Subsequently, Verma et al. (5) conducted a prospective study and found that CR maintained and “CR plus” (ratio of CR and pleural fluid lymphocyte count) improved the specificity of CR in identifying MPE.