Metastatic Count and Local Ablative Therapy Influence Survival Outcomes in Oligometastatic Nasopharyngeal Carcinoma Patients

BACKGROUND: Data suggests that oligometastatic nasopharyngeal cancer (NPC) is associated with better prognosis and this is now incorporated in the American Joint Committee on Cancer and Union for International Cancer Control (AJCC/UICC) 9th Version for NPC staging. We sought to clarify this in a local cohort of oligometastatic NPC patients. METHODS: A retrospective review of 211 metastatic NPC patients, age 22-81 years, treated from 2003 to 2021 at National Cancer Centre Singapore was performed. Forty-nine patients had de novo metastatic disease at diagnosis while 168 patients had relapsed metastatic disease. Kaplan-Meier survival analysis was used to compare overall survival (OS) and progression-free survival (PFS) between different cohorts of patients grouped according to number of discrete metastatic lesions and organs involved. RESULTS: Patients with 3 or less metastatic lesions (n = 88) regardless of number of organs involved demonstrated better median OS (36.2 vs 14.3 months, p < 0.001) and PFS (11.8 vs. 7.2 months, p < 0.001). In patients with metastatic lesions confined to a single organ (n = 116), those with ≤ 3 discrete lesions (n = 75) demonstrated improved median OS (37.8 vs. 16.7 months, p < 0.001) and PFS (12.3 vs. 7.7 months, p = 0.003). Among the patients with ≤ 3 metastatic lesions, those who received aggressive local ablative therapy (LAT) to all metastatic lesions demonstrated better median OS (81.3 vs. 16.7 months, p = 0.013) and PFS (21.0 vs. 9.6 months, p = 0.049). CONCLUSIONS: Three or less discrete metastatic lesions regardless of the number of organs involved is an indicator of limited metastatic burden in NPC and is associated with improved survival outcomes. Our retrospective data validates the definition of oligometastatic disease in the AJCC/UICC 9th Version for NPC staging. Based on our data, these patients should be channeled to LAT approaches and further research should explore sequencing of systemic therapy and LAT.