Patterns of failure in nasopharyngeal cancer patients of northeastern region of India.

94 Background: We aimed to analyze patterns of failure and relationship between disease volume and treatment outcomes in patients of Nasopharyngeal cancer receiving chemoradiation at tertiary cancer centre in northeast region of India. Methods: From February 2018 to February 2022, 99 histopathologically proven non metastatic NPC patients treated with IMRT and chemotherapy were analysed retrospectively. Locally advanced patients received neoadjuvant or adjuvant chemotherapy. Locoregional failures were classified as in-field or out-of-field in relation to the CT data sets used for pretreatment planning. The Cox proportional hazards model was used to investigate the impact of various prognostic factors on locoregional free survival (LRFS), distant metastasis free survival (DMFS), progression free survival (PFS) and overall survival (OS). The log-rank test and Kaplan-Meir curves were used to compare outcome variables based on classified tumour volume as determined by ROC analysis. Results: During a median follow up of 25.4 months (17.3-39.2), 35 (35.4%) patients developed recurrence. Twenty-nine patients developed locoregional failures, of which 11 were in-field; 12 patient showed an out-field failure. The 3-year LRFS, DMFS, PFS and OS was 71.10%, 70.90%, 64.10 and 74.10 % respectively. There was statistically significant difference in locoregional failure-free survival according to T staging (p<0.0001). Cox regression analysis revealed that gross tumor volume(GTVp) and gross nodal volume(GTVn) were an independent prognostic factor for OS, PFS, LRFS and DMFS. The cut-off volumes for GTVp and GTVn for distant metastases and locoregional failure, respectively, were found to be 13 and 22.7 mL and 3.7 and 39.2 mL, respectively, by ROC curve analysis. Based on this, 99 patients were divided into three subgroups. OS demonstrated significant differences among patients in different volume subgroups for GTVp (p=0.03) and GTVn (p=0.00024) and were superior to T classification for predicting prognosis of NPC patients. Conclusions: Distant failure is most common pattern of failure. With advanced T-stage NPC, locoregional failure is more common. GTVp and GTVn are an independent prognostic factor in local control, distant metastasis, disease-free survival, and overall survival in NPC. This justifies their use as quantitative prognostic indicator for NPC.