Post-radiotherapy prognostic nutritional index and lactate dehydrogenase for risk stratification in extensive-stage small cell lung cancer after completion of chemoimmunotherapy and sequential thoracic radiotherapy

Thoracic radiotherapy is used in selected patients with extensive-stage small cell lung cancer (ES-SCLC) after first-line chemoimmunotherapy. However, markers for prognostic reassessment after radiotherapy remain limited. We evaluated the prognostic value of post-radiotherapy prognostic nutritional index (PNI) and lactate dehydrogenase (LDH) in this setting. We retrospectively analyzed 203 patients with ES-SCLC who completed first-line chemoimmunotherapy and sequential thoracic radiotherapy and reached the post-radiotherapy assessment without death or disease progression. PNI and LDH were measured before systemic therapy and 4–6 weeks after thoracic radiotherapy. PNI was dichotomized at 56.7, and LDH was classified using the institutional upper limit of normal of 245 U/L. Overall survival (OS) and progression-free survival (PFS) were calculated from the post-radiotherapy assessment date. Baseline-to-post-radiotherapy PNI transition groups were analyzed separately. During follow-up, 147 deaths and 179 PFS events occurred. Higher post-radiotherapy PNI was independently associated with better OS and PFS, whereas elevated post-radiotherapy LDH was associated with poorer outcomes. Baseline-to-post-radiotherapy PNI transition groups also provided additional prognostic information beyond post-radiotherapy PNI alone ( P = 0.008 for OS and P = 0.016 for PFS). An exploratory post-radiotherapy PNI–LDH risk stratification showed stepwise survival separation, with median OS of 27, 14, and 9 months in the low-, intermediate-, and high-risk groups, respectively. Compared with the low-risk group, the high-risk group had poorer OS (HR, 5.122; 95% CI, 3.103–8.454; P < 0.001) and PFS (HR, 2.918; 95% CI, 1.835–4.642; P < 0.001). Bootstrap internal validation of the main multivariable model yielded optimism-corrected C-indices of 0.685 for OS and 0.641 for PFS. Post-radiotherapy PNI and LDH were associated with subsequent survival in patients with ES-SCLC who reached post-radiotherapy reassessment after chemoimmunotherapy and sequential thoracic radiotherapy. Their combination may provide an exploratory approach to prognostic stratification, but prospective external validation is needed before clinical application.