The usefulness of ProGRP as a marker for differentiating SCLC from non-SCLC has also been proven: the serum concentration of ProGRP in patients with SCLC was significantly higher compared to its concentration in patients with squamous cell carcinoma and adenocarcinoma (85.63 pg/mL vs. 65.48 pg/mL vs. 70.69 pg/mL). The gene discussed is GRP; the disease is adenocarcinoma.