[Clinical significance and key points for interpreting progastrin-releasing peptide and neuron-specific enolase in chemoradiotherapy for limited-stage small cell lung cancer].

Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine tumor. Although it accounts for only about 13% of all lung cancers, its rapid proliferation, early metastasis, and very poor prognosis result in an extremely low five-year survival rate. In recent years, immune checkpoint inhibitors have improved outcomes in a subset of patients; however, the proportion of patients who derive meaningful benefit remains limited. For patients with limited-stage SCLC (LS-SCLC) undergoing chemoradiotherapy (CRT), standardized serum biomarkers suitable for routine monitoring of treatment response and early detection of relapse have yet to be established. Progastrin-releasing peptide (ProGRP) is generally more specific than neuron-specific enolase (NSE) for SCLC, yet neither marker is diagnostic when used alone. This review summarizes the roles of ProGRP and NSE in LS-SCLC during chemoradiotherapy (CRT), with an emphasis on differential diagnosis (particularly when pleural effusion cytology suggests adenocarcinoma but ProGRP is markedly elevated-raising the possibility of SCLC, mixed histology, or transformation and underscoring the need for tissue confirmation), longitudinal monitoring, and prognostic implications. Notably, universally accepted cut-off values for survival prediction are lacking; therefore, clinical interpretation should focus on within-assay dynamic trends and incorporate potential interfering factors, including renal dysfunction and hemolysis.