Lymphocyte Apoptosis as a Predictive Biomarker for Radiation Therapy De-intensification in EBV-Associated Nasopharynx Cancer

Abstract

Severe toxicities occur in head and neck cancer patients despite precision radiotherapy (RT). Emerging evidence in HPV and EBV-associated cancers of the oropharynx and nasopharynx (NPC), respectively, supports the concept of dose de-intensification in these radiosensitive tumors. We hypothesize that patients who develop severe late effects to RT have better tumor control, due to common intrinsic radiosensitivity index. Here, we investigate the utility of radiation-induced lymphocyte apoptosis (RILA) assay to predict clinical outcomes (tumor control and RT induced toxicity) with the secondary objective that these patients could be considered for de-intensification strategies. RILA assay was assessed in a cohort of UICC/AJCC seventh edition TNM Stage III/IVAB NPC patients from a randomized controlled phase III trial (N = 172, NCC0901) of cisplatin-RT with or without induction gemcitabine, carboplatin and paclitaxel. Acute and late toxicities were assessed by CTCAE v.2 at the following intervals (2 mo yr 1, 4 mo yr 2, 6 mo yr 3-5, annually thereafter). We performed the RILA assay (48 h post 8 Gy) in a subset of cases (N = 87). At median follow-up, DFS (3yr 74.9% GCP vs 67.4% Control, P = 0.362) and incidence of severe Grade ≥3 late toxicities did not differ between the treatment arms. In keeping with our hypothesis, severe late effects were associated with reduced risk of disease recurrence [OR 0.19 (95% CI = 0.02 – 1.59, P = 0.08)]. We observed that %RILA was associated with severe late effects [OR 1.92 (95% CI = 0.67 – 5.50, P = 0.17) for high %RILA stratified by highest quartile]. High %RILA was also associated with lower recurrence risk [4.5% (1 failure/22), high %RILA vs 19.7% (12 failures/61), low %RILA; OR 0.19, (95% CI = 0.02 – 1.59, P = 0.08)] suggesting common molecular determinants of radiosensitivity. Subset analyses of CD4+ and CD8+ subpopulation of immune cells suggest that RILA responses were correlated (Spearman R = 0.67, P < 0.001); therefore we examined and observed that patients with %RILAHigh CD4+/ High CD8+ (N = 13) were strongly associated with a reduced risk of recurrence [OR 0.81 (95% CI = 0.73 – 0.91, P = 0.09)] compared to patients with %RILAHigh CD4+/ Low CD8+ and %RILALow CD4+/ High CD8+. Herein, we showed that %RILA may be a useful biomarker for tumor and normal tissue radiosensitivity of EBV-associated NPC. If validated, this predictive assay will enable precision matching of RT sensitive patients for de-intensification strategies in EBV and other viral associated head and neck cancers. The association between tumor control and sub-population of immune cells suggests immune dependency on RT effects and requires further interrogation.