External Validation of a Nomogram to Predict Survival and Benefit of Concurrent Chemoradiation for Stage II Nasopharyngeal Carcinoma

SIMPLE SUMMARY: The optimal treatment strategy (concurrent chemoradiation (CCRT) vs. radiotherapy alone) for stage II nasopharyngeal carcinoma (NPC) in the intensity-modulated radiotherapy (IMRT) era is controversial across guidelines. A nomogram by Sun et al. was published to predict the overall survival (OS) benefit of CCRT based on a patient’s clinical parameters. Using the cohort from the Hong Kong NPC1301 study, we evaluated the external validity of the nomogram and the associations between the proposed clinical factors and OS among stage II NPC patients. Use of CCRT was an insignificant predictor for OS. The nomogram lacked the predictive accuracy and should be interpreted with caution. ABSTRACT: A nomogram was recently published by Sun et al. to predict overall survival (OS) and the additional benefit of concurrent chemoradiation (CCRT) vs. radiotherapy (RT) alone, in stage II NPC treated with conventional RT. We aimed to assess the predictors of OS and to externally validate the nomogram in the IMRT era. We analyzed stage II NPC patients treated with definitive RT alone or CCRT between 2001 and 2011 under the territory-wide Hong Kong NPC Study Group 1301 study. Clinical parameters were studied using the Cox proportional hazards model to estimate OS. The nomogram by Sun et al. was applied with 1000 times bootstrap resampling to calculate the concordance index, and we compared the nomogram predicted and observed 5-year OS. There were 482 patients included. The 5-year OS was 89.0%. In the multivariable analysis, an age > 45 years was the only significant predictor of OS (HR, 1.98; 95%CI, 1.15–3.44). Other clinical parameters were insignificant, including the use of CCRT (HR, 0.99; 95%CI, 0.62–1.58). The nomogram yielded a concordance index of 0.55 (95% CI, 0.49–0.62) which lacked clinically meaningful discriminative power. The nomogram proposed by Sun et al. should be interpreted with caution when applied to stage II NPC patients in the IMRT era. The benefit of CCRT remained controversial.