The area under the curve (AUC) for KL-6 was larger than that for SP-D and MMP-2 (Fig. 3), indicating that the order of diagnostic accuracy by the ROC curve was KL-6, SP-D, and MMP-2 in patients with asbestosis alone or in both patients with asbestosis and those with silicosis. Here, SFTPD is linked to silicosis.