Development and validation of a novel nomogram integrating visceral-to-subcutaneous fat ratio and neutrophil-percentage-to-albumin ratio for overall survival in locally advanced rectal cancer undergoing neoadjuvant radiotherapy.

Background: Emerging evidence suggests that neutrophils are preferentially recruited to visceral adipose tissue, connecting adipose distribution to systemic inflammation. Visceral fat accumulation and systemic inflammation-nutrition status are known to affect cancer prognosis, yet no existing prognostic model integrates visceral-to-subcutaneous fat ratio (VSR) and neutrophil-percentage-to-albumin ratio (NPAR). This study aimed to develop and validate a cost-effective nomogram incorporating VSR and NPAR to predict overall survival (OS) for locally advanced rectal cancer (LARC) patients who underwent neoadjuvant radiotherapy (nRT). Methods: A total of 143 LARC patients receiving nRT followed by total mesorectal excision were retrospectively enrolled. The CT images from radiation CT-Simulator System were used to assess VSR, and routine blood tests were conducted to calculate NPAR and other inflammatory-nutritional markers without extra cost or radiation. LASSO-Cox regression was used to identify independent predictors for OS and a nomogram was constructed and internally validated using 1000 bootstrap resamples. Model performance was assessed through concordance index (C-index), time-dependent receiver operating characteristic (ROC) curves, calibration curves, and decision curve analysis (DCA), and compared with the TNM staging system and pathological complete response (pCR) using discriminant indices. Results: The median follow-up time was 72.8 months. LASSO-Cox regression identified VSR (HR = 3.755, P = 0.009), NPAR (HR = 3.626, P = 0.003), CA199 (HR = 4.052, P = 0.001), and neural invasion (HR = 2.666, P = 0.047) as independent risk factors for OS. The nomogram showed an original C-index of 0.781, with a bootstrap-corrected value of 0.775. Its AUC values for 3-, 5-, and 8-year OS were 0.816, 0.777, and 0.867, respectively. Calibration curves revealed optimal agreement between predicted and actual observed outcomes, and DCA suggested better clinical net benefits than individual factors. The model demonstrated strong accuracy, discriminative ability, and clinical utility, outperforming TNM staging system and pCR in long-term predictions. Kaplan-Meier analysis demonstrated significantly worse OS in high-risk group (Log-rank P<0.001). Conclusion: This novel nomogram integrating VSR and NPAR demonstrates favorable long-term prognostic performance for LARC patients following nRT, compared to TNM staging and pCR. Since both markers are obtained from routine radiation simulation CT and blood tests without additional radiation or cost, this cost-effective and accessible model may facilitate risk-based surveillance and personalized therapy in clinical application.