Stroke after Radiotherapy to Treat Head and Neck Cancer - What is the Risk?
Head and Neck Cancer , Radiotherapy , Stroke
Background: Head and Neck cancers (H&NCa) are typically associated with risk factors such as smoking and alcohol use. The human papilloma virus (HPV) has begun to play a role in the pathogenesis of these cancers, decreasing the age of diagnosis and increasing survival. Curative H&NCa treatments can include surgery (SX) and radiotherapy (RT) and one of the suggested late effects of RT is damage to blood vessels. The current literature identifies vascular injury and stroke as possible outcomes following RT among patients with H&NCa. Objectives: 1) To determine the risk of ischemic stroke among patients that received any curative RT compared to patients that were treated with SX alone, and quantify this risk with respect to time following treatment, 2) to determine how modifications of RT regimens affect the risk of ischemic stroke, specifically the addition of chemotherapy, preceding the RT with surgical neck dissection and different doses of radiation, and 3) to determine the risk of stroke-related events, including transient ischemic attacks and carotid endarterectomies/stents, among patients that were treated curatively with any RT compared to patients treated with SX alone. Methods: A retrospective cohort design using incident cases of H&NCa identified through the Ontario Cancer Registry was used to address these objectives. The risk of stroke following RT was assessed using databases from the Institute of Clinical Evaluative Sciences. The risk of – and time to stroke was be examined using a survival analytic approach, accounting for the competing risk of death. Cause-specific Cox proportional hazards models adjusted for stroke risk factors and cumulative incidence functions were estimated for each objective. Results: The study cohort included 14,069 patients with H&NCa. RT was found to contribute considerably to the risk of stroke compared to SX - both alone (HR=1.70, 95%CI: 1.41,2.05) and after combining all treatment modalities that included any radiation exposure (HR=1.46, 95%CI: 1.23,1.73). Conclusion: This study’s results show that RT contributes a risk of stroke in terms of a late effect of treatment. These findings were consistent with biological hypothesis and contribute a significant and important addition to the body of literature.