Prognostic Significance of Modified Shine and Lal Index in Patients with Non-Small Cell Lung Cancer Undergoing Surgical Resection

<b>Background</b>: Although white blood cell-related indices are established prognostic markers in lung cancer, the prognostic significance of red blood cell (RBC) indices-mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC)-remains unclear. This study assessed the prognostic value of RBC indices for predicting survival outcomes in patients who underwent curative-intent surgery for stage I-IIIA non-small cell lung cancer (NSCLC). <b>Methods</b>: This retrospective analysis of 437 patients evaluated the prognostic significance of MCV, MCH, MCHC, and the modified Shine and Lal Index (mSLI), calculated as (MCV² × MCH) × 0.0001, using Cox regression analysis. Model performance was evaluated using various metrics, including the concordance index (C-index) and integrated discrimination improvement (IDI). <b>Results</b>: In the multivariate Cox regression analysis, each RBC index was tested separately as an overall survival (OS) predictor in models that consistently included age, American Society of Anesthesiologists Physical Status (ASA-PS), pleural invasion, tumor-node-metastasis (TNM) stage, and the Noble and Underwood (NUn) score. Given its superior predictive performance, the mSLI model, which incorporates mSLI in addition to other covariates, was finalized and outperformed the baseline TNM staging model (C-index: 0.840 vs. 0.708, <i>p</i> < 0.001) and demonstrated significant improvements in IDI at 3 and 5 years (<i>p</i> < 0.001). Compared to the intermediate model-comprising the same covariates as the mSLI model except for mSLI-the mSLI model showed a slightly higher C-index (0.840 vs. 0.835, <i>p</i> = 0.554) and significant improvements in IDI at 3 years (<i>p</i> = 0.008) and 5 years (<i>p</i> = 0.020). <b>Conclusions</b>: mSLI was an independent prognostic marker for OS in stage I-IIIA NSCLC, enhancing risk stratification and providing incremental predictive value beyond that of traditional models. Incorporating mSLI into prognostic frameworks may improve clinical decision-making. However, external validation is required to confirm its clinical utility.