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.