Next, we further analyzed the patients in the test group and found that the levels of MMP-2 and MMP-9 in NSCLC patients were decreased more dramatically than those in SCLC patients (P <  0.05), while there was no significant difference in the levels of CD8+, CD4+ and CD4+/CD8+ (Figure S2 D-F). Here, MMP9 is linked to small cell lung carcinoma.