Use of external beam radiotherapy is associated with reduced incidence of second primary head and neck cancer: A seer database analysis

Purpose: Patients with head and neck cancer have a significant risk of developing a second primary cancer of the head and neck. We hypothesized that treatment with external beam radiotherapy (RT) might reduce this risk, because RT can eradicate occult foci of second head and neck cancer (HNCA). Methods and Materials: The data of patients with Surveillance, Epidemiology, and End Results Historic Stage A localized squamous cell carcinoma of the oral cavity, larynx, and pharynx were queried using the Surveillance, Epidemiology, and End Results database. For patients treated with or without RT, the incidence of second HNCA was determined and compared using the log-rank method. Cox proportional hazards analysis was performed for each site, evaluating the influence of covariates on the risk of second HNCA. Results: Between 1973 and 1997, 27,985 patients were entered with localized HNCA. Of these patients, 44% had received RT and 56% had not. The 15-year incidence of second HNCA was 7.7% with RT vs. 10.5% without RT (hazard ratio 0.71, p < 0.0001). The effect of RT was more profound in patients diagnosed between 1988 and 1997 (hazard ratio 0.53, p < 0.0001) and those with pharynx primaries (hazard ratio 0.47, p < 0.0001). On multivariate analysis, RT was associated with a reduced risk of second HNCA for pharynx (p < 0.0001) and larynx (p = 0.04) tumors. For oral cavity primaries, RT was associated with an increased risk of second HNCA in patients treated before 1988 (p < 0.001), but had no influence on patients treated between 1988 and 1997 (P = 0.91). Conclusion: For localized HNCA, RT is associated with a reduced incidence of second HNCA. These observations are consistent with the eradication of microscopic foci of second HNCA with external beam RT. (c) 2008 Elsevier Inc.