Our results show that APE1 is a strong biomarker for NSCLC, and that combining it with a previously recognized biomarker for NSCLC, CEA, further enhances the power of both, but the use of sAPE1 as a biomarker for other cancers, such as small cell lung cancer (SCLC), needs to be explored. The gene discussed is APEX1; the disease is small cell lung carcinoma.