The development and external validation of simplified T category classification for nasopharyngeal carcinoma to improve the prognostic value in the intensity‐modulated radiotherapy era

BACKGROUND: Intensity-modulated radiotherapy (IMRT) provides excellent local control in nasopharyngeal carcinoma (NPC). We investigated whether simplifying 8th American Joint Committee on Cancer staging system T categories improves prognostic value. METHODS: We used 2191 NPC patients as a training set and 414 patients separately as an independent, external validation cohort. RESULTS: In the training set, local relapse-free survival (LRFS), disease-free survival (DFS), and overall survival (OS) were not significantly different between the 8th edition T2/T3 (P = 0.610, 0.380 and 0.353, respectively). Merging T2 and T3 to proposed T2 (proT2) provided significant differences in LRFS, DFS, and OS between proposed T categories. Proposed T categories had similar c-indices for LRFS, DFS, and OS (vs the 8th edition), which was validated in the external cohorts. Moreover, for DFS, the adjusted HRs of the proT2N0 (3.8), proT1N1 (3.8), and proT2N1 (6.0) subsets were similar; the adjusted HRs of the proT3N0 (7.0), proT3N1 (11.4), proT1N2 (11.0), proT2N2 (11.6), and proT3N2 (13.3) subsets were similar; the adjusted HRs of the proT1N3 (17.8), proT2N3 (15.3), and proT3N3 (26.4) subsets were similar; the results of the adjusted HRs for OS had the same rule. Defining proT1N0 as stage I; proT1N1/proT2N0-1 as stage II; proT3N0-2/proT1-2N2 as stage III; and proT1-3N3 as stage IVa generated orderly, significant differences in DFS and OS between stages in the training set and external validation cohort. CONCLUSIONS: In the IMRT era, three T categories are more reasonable (merging T2/T3 into T2) and proT3N0-2 (the 8th edition T4N0-2) should be down-staged to stage III.