Correlation between nasopharyngeal carcinoma tumor volume and the 2002 International Union Against Cancer tumor classification system

Background: The correlation between primary tumor volume and nasopharyngeal carcinoma (NPC) UICC 2002 T classification, N classification and distant metastasis after radiation therapy was discussed to provide further evidence for the inclusion of tumor volume into the TNM classification staging system. Methods: Between February 2001 and December 2008, 666 patients with NPC treated with intensity-modulated radiation therapy (IMRT) were analyzed retrospectively. Primary gross tumor volume was calculated from treatment planning computed tomography scans. The Kruskal-Wallis and Mann-Whitney tests were used for comparison of continuous variables and the chi-square test was used for categorical variables. A logistic regression model was used for multivariate analysis. Results: Median primary tumor volume of the 666 patients was 20.35 ml (range, 0.44 - 192.63 ml), and it gradually increased with T classification. Statistically significant differences in tumor volume were observed between patients with different T classifications (p < 0.001). The cervical lymph node metastasis rate was 64.7% (430/666); the differences in primary tumor volume between patients with or without lymph node metastasis were statistically significant (p < 0.001). Posttreatment distant metastasis occurred in 100 NPC patients, and the five-year distant metastasis-free survival was 84.2%. Univariate and multivariate analyses showed that N classification (p < 0.001) and tumor volume (p = 0.007) were the main factors influencing distant metastasis. Conclusion: Tumor volume was correlated with T classification, cervical lymph node mestastasis and distant metastasis after radiation therapy in nasopharyngeal carcinoma, suggesting that tumor volume should be included into the TNM staging system.