Risk, pattern and survival impact of second primary tumors in patients with nasopharyngeal carcinoma following definitive intensity-modulated radiotherapy

Aim Second primary tumor (SPT) is a serious late complication after definitive radiotherapy for nasopharyngeal carcinoma (NPC). We evaluated the incidence, pattern, risk factors and survival impact of SPT in NPC patients following definitive intensity-modulated radiotherapy (IMRT). Methods A retrospective review of 780 consecutive IMRT-treated NPC patients between February 2003 and September 2011 was conducted. Cumulative SPT incidence and overall survival after SPT diagnosis were estimated. Associations between clinical characteristics and SPT risk were analyzed. Standardized incidence ratios (SIR) were calculated using age, gender and calendar-year-specific cancer incidences from the Hong Kong Cancer Registry. Results At a median follow-up of 7.5 years, 51 SPTs (6.7%) were identified, 22 (43.1%) of which occurred within previous radiotherapy fields. Tongue cancers (31.8%) and sarcomas of the head and neck (31.8%) were the most common in-field SPTs. Age [hazard ratio (HR), 1.051; 95% confidence interval (CI), 1.025-1.078] and smoking status (HR, 1.755; 95% CI, 1.002-3.075) were independent risk factors associated with SPT development. Median overall survival after SPT diagnosis was 2.9 years. There was an 84% increase in cancer risk (SIR, 1.84; 95% CI, 1.37-2.42) compared with the general population. Significant excess risks were observed for sarcoma, tongue, oropharyngeal, prostate and liver cancer. Excess risks were higher beyond 5 years of follow-up. Conclusion Substantial risk of SPT, especially for in-field sarcoma and tongue cancers, exists after definitive IMRT for NPC. SPT severely negates longevity of NPC survivors. High awareness and careful surveillance is warranted for this late lethal complication.