Background: Progastrin-releasing peptide (ProGRP) is a potential marker for small-cell lung cancer (SCLC) in serum; however, it may be more stable in plasma. We investigated a new plasma assay (ProGRPp) and its usefulness in diagnosing and monitoring SCLC.
Methods: The marker concentrations were determined on the ARCHITECT i system.
Results: The assay could distinguish SCLC from non-small-cell lung cancer (NSCLC: area under the curve 0.931, 95% CI 0.893-0.969; cross-validated accuracy 0.813; sensitivity 84.0%, specificity 96.3%; at 140 pg ml(-1) cutoff). The probability of SCLC when ProGRPp was >140 pg ml(-1) was 91.8%, after adjusting for age, gender, and renal dysfunction. The NSCLC patients with ProGRPp >140 pg ml(-1) were at high risk (odds ratio=37.0, P<0.001) for tumours with neuroendocrine features. False negatives in SCLC were associated with a lack of thyroid transcription factor-1 (P<0.001). A decrease of ProGRPp to <140 pg ml(-1) during chemotherapy was significantly associated with the image-based response (P<0.001), and independently affected progression-free survival (PFS, relative risk=2.51, P=0.04) and overall survival (OS, relative risk=4.38, P=0.003), after adjustment for imaging response, performance status, and stage.
Conclusions: The ProGRPp assay is specific and sensitive for diagnosing SCLC. Changes in ProGRPp during chemotherapy are significantly associated with image-based response, PFS, and OS.