Empowering patients to make informed decisions on cancer prevention
A new paradigm in cancer prevention – taking medication to reduce the risk of developing cancer (‘chemoprevention’) – is beginning to enter the realms of primary care for specific groups of patients.
To date, prevention of cancer in primary care has focused on modifying behaviours associated with increased risk of cancer (primary prevention) or increasing participation in national cancer screening programs (secondary prevention). Chemoprevention focuses on the use of medication to lower risks, delay development or recurrence, or prevent cancer.
There is strong evidence for the use of low-dose aspirin for the prevention of colorectal cancer in people aged 50–70 years, and the use of selective oestrogen receptor modulators (SERMs) for women at increased risk of breast cancer. All medications have potential side effects and researchers from the University of Melbourne Cancer in Primary Care Research Group have evaluated two methods for explaining the potential harms and benefits of cancer chemoprevention to encourage informed consent.
The study explored the clinical implications of relatively new Australian guidelines on prescribing risk-reducing medication, released by the National Health and Medical Research Council in 2017, led by Cancer Council Australia with contributions from Professor Jon Emery of University of Melbourne.
Figure 1. Expected frequency trees showing the effects of aspirin on the incidence of events over 10 years of taking aspirin for at least five years in Australian men and women aged 50–70 years (graphics designed by Kara-Lynne Cummings)
Studies have found that taking aspirin for as little as 2.5 years can reduce the incidence of colorectal cancer, with people at increased risk of colorectal cancer more likely to benefit than those at average risk of bowel cancer. Overall, studies found that the benefits (such as reducing the risk of non-fatal heart attacks as well as the reduction in bowel cancer) significantly outweighed potential harms from aspirin use, which include gastrointestinal bleeding.
For example, it is estimated that for a person aged 50 years, taking aspirin for 10 years is 10 times more likely to prevent death than cause it, and five times more likely for someone aged 65 years.
The authors, including Professor Jon Emery, Dr Jennifer Walker, Dr Jessica Minshall, Ms Kara-Lynne Cummings and Mr Peter Nguyen, developed novel risk communication methods including ‘expected frequency trees’ for an Australian population of 10,000 men and women aged 50–70 years, which show likely outcomes over 10 years of taking aspirin for at least five years. These graphical summaries aim to simplify multiple probabilities and present the likelihood of specific outcomes, to help patients make more informed decisions.
Peter Nguyen, an author on the paper and Research Officer in the Cancer in Primary Care group at the University of Melbourne, conducted a study with GP patients to evaluate different risk communication methods including the expected frequency tree for aspirin use and noted the importance of involving patients in the treatment choice process.
“There is a shift towards encouraging shared decision making, showing patients the benefits and harms to inform whether they want to take medications for cancer prevention,” Mr Nguyen said.
“This research clearly shows that the benefits of taking aspirin for colorectal cancer prevention still outweigh any potential harms in the cohort of 50–70 year-old patients, even over long periods of time.”
For breast cancer prevention, several randomised controlled trials have shown that drugs such as tamoxifen and raloxifene (so-called SERMs) significantly reduce the risk of breast cancer in women who have no personal history of the condition.
Analysis of data from nine prevention trials showed 38% reduced incidence of breast cancer, with the participants including women at increased risk of breast cancer as well as those at average risk, and a wide range of age groups, both premenopausal and postmenopausal.
The expected frequency trees developed by the research group aim to clearly display both benefits and side-effects of taking three different SERMs for chemoprevention for breast cancer.
Figure 2. Expected frequency trees for Australian females at moderate risk of breast cancer, showing the effects of taking tamoxifen and raloxifene for five years (graphics designed by Kara-Lynne Cummings)
The guidelines for aspirin and SERMs reflect a new approach to cancer prevention in primary care. The decision to prescribe these drugs involves careful discussion about the potential benefits and harms to an individual patient and consideration of underlying disease risks – making the decision trees important tools to guide and inform prevention discussions with patients.
The study suggested that women with a family history of breast cancer who are interested in exploring SERMs for chemoprevention may be better referred to a familial cancer clinic or specialist breast cancer service. However, the discussion about taking aspirin for colorectal cancer prevention could sit well within primary care.