Progastrin-releasing peptide as a diagnostic and therapeutic biomarker of small cell lung cancer

Background: Progastrin-releasing peptide (proGRP) is a recently identified biomarker of small cell lung cancer (SCLC). We evaluated the usefulness of plasma proGRP level as a tumor marker for diagnosis and treatment monitoring in patients with SCLC.

Methods: Plasma samples were collected prospectively from 452 [212 non-small cell lung cancer (NSCLC), 105 SCLC, and 135 other diseases] patients who visited the hospital for tissue diagnosis. Plasma proGRP levels were measured using a two-step automated immunoassay.

Results: The median proGRP level was significantly higher in patients with SCLC (892.7 pg/mL) than those with NSCLC (32.6 pg/mL, P<0.001) and other diseases (26.6 pg/mL, P<0.001). At cutoff level of 63 pg/mL, proGRP shows 85.7% sensitivity, 90.2% specificity, 72.5% positive predictive value and 95.4% negative predictive value in patients with SCLC. The area under the curve values were 0.93 for distinguishing SCLC from NSCLC, and 0.943 for distinguishing SCLC from the other conditions. Median proGRP level was higher in extensive disease (1,055.2 pg/mL) than limited disease (253.8 pg/mL, P=0.005). Median OS was significantly shorter in patients with extensive disease (6.0±0.7 months) than limited disease (12.7±4.5 months, P<0.01). Among the 39 patients with SCLC who were followed, the median proGRP levels of the 23 responders decreased after chemotherapy (P<0.001).

Conclusions: Plasma proGRP level could be a useful diagnostic and therapeutic monitoring biomarker for patients with SCLC and the initial level may help with SCLC tumor staging.