In the second comparison, a classification tree which sequentially included the proteins CA19-9, CA15-3, MMP-3, and kallikrein-12 (Figure 2B) yielded a sensitivity of 83% (95% CI 64.2–94.2%) and a specificity of 89.7% (95% CI 73–98%) for separating 29 lung adenocarcinomas from 29 mesotheliomas. Here, KLK12 is linked to mesothelioma.