Impact Of Adjuvant Chemotherapy And Cumulative Cisplatin Dose In Locally Advanced Nasopharyngeal Carcinoma (La-Npc) Treated With Definitive Chemoradiotherapy.

6046 Background: Total cumulative cisplatin dose (CDDP-D) (concurrent/induction/adjuvant) in multimodality therapy for LA-NPC has been associated with survival at centers in Asia. We evaluated the survival impact of adjuvant chemotherapy (adj chemo) and total CDDP-D in a large, single institution Canadian cohort of LA-NPC. Methods: Patients (Pts) withWHO type II and III LA-NPC treated with concurrent IMRT with high-dose CDDP and adj chemo with CDDP/Carboplatin and 5-FU (maximum total/adjuvant CDDP-D= 540/240 mg/m2) between 2003-2016 were analyzed. EBER status was tested by ISH. Staging was classified by UICC/AJCC7thedition TNM. Kaplan-Meier 5-year (5y) for overall survival (OS) and recurrence-free survival (RFS) were calculated and compared by log-rank test betweenstage, adj chemo (yes vs no) and total CDDP-D (>300 vs ≤300mg/m2). Multivariable analysis (MVA) identified survival predictors. Results: A total of 312 pts were evaluated: median age = 49.8 (range 17.4-75.9); EBER+/-/unknown=67%/1%/32%; stage II/III/IV=2%/51%/47%; T4=36%; N3=17%; adj chemo=83% (21% switched to carboplatin); median total/adjuvant CDDP-D=380/160 mg/m2; median follow-up 7.6 years (range 0.6-14.9). 5y OS differed by stage II-III vs IV (95% vs 80%, p<0.001) and total CDDP-D >300 vs ≤300mg/m2 (89% vs 83%, p=0.02). Adj chemo and total CDDP-D impacted 5y OS in stage IV (table). 5y RFS was higher in stage IV with total CDDP-D >300 vs ≤300mg/m2 (74% vs 59%, p=0.03), with a trend in locoregional control (LRC) (91% vs 80%, p=0.05) but not significant on distant control (DC) (78% vs 72%, p=0.36). Conclusions: Total CDDP-D >300 mg/m2 impacts OS in the overall cohort. The benefit of adj chemo and total CDDP-D on OS and RFS is significant in stage IV but not stage II-III LA-NPC, mainly due to higher LRC rather than DC. [Table: see text]