Head and Neck Cancer

PV QA 2 - Poster Viewing Q&A 2

MO_28_2661 - Prognostic Model for Stratification of Radioresistant Nasopharynx Carcinoma to Curative Salvage Radiation Therapy

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Prognostic Model for Stratification of Radioresistant Nasopharynx Carcinoma to Curative Salvage Radiation Therapy
Y. Li1, Y. Tian2, S. H. Tan1, M. Liu3, G. Kusumawidjaja1, E. H. W. Ong1, C. Zhao3, T. W. K. Tan1, K. W. Fong1, K. Sommat1, S. Y. Lim1, F. Han3, and M. L. K. Chua1; 1National Cancer Centre Singapore, Singapore, Singapore, 2Huizhou Municipal Central Hospital, Huizhou, China, 3Sun Yat-Sen University Cancer Center, Guangzhou, China

Purpose/Objective(s): For locally recurrent nasopharynx carcinoma (lrNPC) after radical radiotherapy, another course of intensity modulated radiotherapy (IMRT) is the only curative option for unresectable patients (pts). The prognosis of IrNPC is heterogeneous, and severe RT- related toxicities account for up to 50% mortality after salvage IMRT. We therefore developed and validated a prognostic index (PI) to personalize recommendations for salvage IMRT in pts with lrNPC.

Materials/Methods: We utilized a cohort of 558 cases of lrNPC for PI construction and validation; patients were treated at two academic centers (Sun Yat-Sen University Cancer Center [SYSUCC-A; n = 251 (training cohort, TC)] and National Cancer Centre Singapore [NCCS; n = 114] and SYSUCC-B [n = 193 (validation cohorts, VCs)]) and underwent salvage IMRT from 2001 to 2015. Primary and secondary end points were overall survival (OS) and grade 5 toxicity-free rate (G5-TFR). Covariate inclusion to the PIs was qualified by a multivariable two-sided P < 0.05. Discrimination and calibration of the PIs were assessed.

Results: The primary PI comprised covariates adversely associated with OS in the TC (GTVrecurrence HR = 1.01/mL [P< .001], agerecurrence HR = 1.02/y [P = .008]; re-IMRT equivalent dose in 2-Gy fractions [EQD2] ≥68 Gy HR = 1.42 [P = .03]; prior RT-induced grade ≥3 toxicities HR = 1.90 [P = .001]; rT3-4 HR = 1.96 [P = .005]). Discrimination of the PI for OS was comparable between TC and both VCs (Harrell’s C = 0.71 [SYSUCC-A], 0.72 [NCCS], and 0.69 [SYSUCCB]); discretization by using a fixed PI score cut-off of 252 determined from the TC yielded low- and high-risk groups with disparate OS in the VCs (NCCS HR = 3.09 [95% CI =1.95-4.89]; SYSUCC-B HR = 3.80 [95% CI = 2.55-5.66]). Our five-factor clinical PI predicted OS and G5-TFR (predicted v observed 36-month OS and G5-TFR, 22% v 15% and 38% v 44% for high-risk NCCS and 26% v 31% and 45% v 46% for high-risk SYSUCC-B).

Conclusion: We present a validated PI for robust stratification of radioresistant NPC. Low-risk pts represent ideal candidates for curative repeat IMRT, whereas novel clinical approaches are needed in the high-risk group.

Author Disclosure: Y. Li: None. Y. Tian: None. S. Tan: None. G. Kusumawidjaja: None. E.H. Ong: None. K. Sommat: None.

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