Benefits and Harms of Preventive Therapy for Cancer
1Queen Mary University of London, London, UK
The development of preventive therapy for cancer is still in its infancy, and much can be learned from cardiovascular medicine, where it has now become firmly established. This is due to the existence of agents with clearly proven efficacy and minimal side-effects, such as the statins for cholesterol-lowering and the antihypertensive agents to control blood pressure. For cancer, with the exception of vaccination again the human papillomavirus to prevent cervix cancer and hepatitis B to prevent liver cancer, currently available efficacious medicines carry a higher side-effect profile, and minimally toxic agents do not have well established efficacy profiles.
Because most effective cancer preventive agents carry a toxicity burden it becomes very important to target preventive therapy to individuals who stand to benefit most. This has two major elements: an accurate risk assessment to identify those at greatest risk of a given cancer, and an ability to identify those at greatest risk of side-effects in order to avoid treatment or to take special precautions, such as those predisposed to gastrointestinal bleeding for aspirin.
In this talk I contrast two different cases for preventive therapy - aspirin and endocrine therapy. For aspirin the benefits are seen for a range of different cancers, making identification of high risk individuals difficult. For most individuals there are no side effects and the potential benefits outweigh the potential harms, but it is highly desirable to identify the small subset most likely to suffer side effects (gastrointestinal and cerebral bleeding) and to not offer aspirin to them.
In the case of endocrine agents such as tamoxifen or the aromatase inhibitors, the benefit is expected only for breast cancer and minor side effects are common and rare but serious side effects also exist so that the identification of high risk individuals for this cancer becomes a key priority.