Second primary malignancies associated with nasopharyngeal carcinoma in Hong Kong: Incidence and risk factors

Background
Improvements in cancer therapies have led to significant increases in survival for nasopharyngeal carcinoma (NPC). While numerous studies have examined SPTs in cancer survivors, only a few have looked at SPTs associated with NPC, which is rare in most of the world, but is the most common cancer in young adults in Hong Kong. These studies have produced inconsistent results in regards to whether NPC patients are at increased risk of SPTs. No previous studies have examined risk factors for SPTs in NPC survivors.  

 Methods
Medical records were reviewed for a retrospective cohort of 1500 NPC patients from two Hong Kong oncology centers. Data were collected on incidence of cancers before and after the index NPC case, demographics variables, smoking history, and variables related to disease characteristics and treatment. Standardized incidence ratios (SIR) were estimated and the Cox proportional hazards model was used to estimate relative risks (RR) corresponding to potential predictors for SPTs.

 Results
There were a total of 98 additional malignancies (SIR = 1.23, 95% CI = 1.00-1.50), with females having greater excess risk (SIR = 1.77) than males (SIR = 1.10). Statistically significant excesses were noted for tongue (9 cases, SIR = 16.60) and brain (4 cases, SIR = 7.05) cancers, and non-significant excesses for leukemia/lymphoma and lung cancer. Significant risk factors for SPTs included older age at NPC diagnosis, having received a parapharygeal radiation boost during treatment, not having received chemotherapy and having previously smoked.

 Discussion
Our study results support the idea that NPC survivors have excess risk of some types of SPTs.  Physicians should be aware of the risk of SPTs for NPC survivors when they plan patient follow-up. The gender difference in SPT risk warrants further study.

        Acknowledgements

       This research was supported by Hong Kong Research Grants Council Competitive Earmarked 
      Grant: CUHK 4531/06M.