Cancer Research UK
Tuesday, 14 March 2017
Using drugs to prevent certain cancers has been in the news a lot [recently], particularly in relation to breast cancer.
We think that the use of drugs to try to prevent cancers – so-called chemoprevention – has fantastic potential to save lives. This is because chemoprevention can reduce the risk of cancer developing in the first place.
But it may be that not all people who could benefit from these drugs are doing so. According to data presented at the San Antonio Breast Cancer Symposium in the US in December, women taking the drug tamoxifen to prevent breast cancer could be mistaking symptoms due to other causes for side effects, making them less likely to keep taking the drug.
This is despite the preventive effects of tamoxifen being shown to last for more than 20 years.
On top of this, draft guidance from National Institute for Health and Care Excellence (NICE) recently recommended a different drug, anastrozole, to prevent cancer in some women who are at a higher risk due to their family history.
But do GPs know of the potential benefit chemoprevention holds?
As part of a new report published [last month], we asked over 1,000 GPs across the UK for their opinions. We wanted to know what they thought about offering tamoxifen and aspirin to lower the risk of, or prevent, certain cancers.
We found nearly half of GPs were unaware of the benefits of tamoxifen to prevent breast cancer among women with a clear family history of the disease who are therefore at higher risk.
There is national guidance in place that recommends the drug for these women, but our study shows more needs to be done to ensure GPs are given the support they need to share these benefits with their patients.
So what can be done?
Why is chemoprevention important?
A number of studies have shown that chemoprevention has the potential to save many lives by stopping cancer developing in the first place.
For example, we funded the International Breast Cancer Intervention Study (IBIS-1) showing that tamoxifen reduces the number of breast cancers diagnosed among women at a high risk of the disease by over 30%.
Research has also shown the benefits of aspirin in preventing bowel and other cancers, although the drug still carries some risks.
And we’re funding studies looking at aspirin in more detail, including the CAPP3 trial, which is looking at the best dose of aspirin to prevent bowel cancer in people with a condition called Lynch Syndrome, who have a higher risk of the disease.
But more needs to be done to communicate the benefits, as well as the risks, of these drugs more widely.
Plus, more support is needed to help those taking the drugs to understand and manage the side-effects that may be linked to their treatment.
What do we know?
Chemoprevention is a relatively new approach to preventing cancer.
But until now it wasn’t clear how much GPs knew of the benefits of these drugs and the support they would like when advising people of the benefits.
“There was a real need for research in the area,” says Dr Samuel Smith from the University of Leeds who led our study. “Our earlier work had suggested GPs were lacking the support to effectively discuss the risks and benefits of preventive therapy – as well as prescribe it to those who were interested in using it.”
An estimated quarter of a million women in the UK are at increased risk of breast cancer and are eligible for preventive drugs, according to NICE guidance. But, because the data isn’t collected, we don’t know on a national level how many people are offered preventive drugs and how many subsequently chose to take these. Or how many cases of cancer could be prevented if more people who could benefit started taking them.
And research has shown that there may be problems with making chemoprevention part of routine clinical practice.
What did we find?
- 24% of GPs were aware of NICE guidance for tamoxifen
- 20% of Scottish GPs were aware of similar national guidelines
- 63% of GPs said they wanted a second opinion before writing the prescription
We deliberately chose a drug that’s covered by NICE and Healthcare Improvement Scotland (HIS) guidance (tamoxifen) and compared awareness to a drug that isn’t, aspirin. This is despite there being evidence that aspirin can reduce the risk of certain cancers.
Although covered by existing guidance, nearly half of the GPs we spoke to were unaware of the benefits of tamoxifen.
Only around a quarter (24%) knew that NICE recommends tamoxifen for women at an increased risk of breast cancer due to their family history (only one in five Scottish GPs were aware of the similar national guidelines).
Despite the low levels of awareness, GPs were willing to prescribe tamoxifen when told of the benefits. But they want more support in doing so.
For example, nearly two thirds (63%) said they wanted a second opinion before deciding to write the prescription. Most commonly with a specialist in secondary care, for example someone from the family history clinic.
Plus, the GPs in our survey were more comfortable if they were told that their patient had already been assessed by a local family history clinic and the doctor there had written the first prescription.
The GPs role in this instance would be in continuing the prescription that had been initiated in secondary care.
When it came to aspirin, most GPs were aware of its cancer prevention potential and felt comfortable discussing the risks and benefits with a person who wanted to take it to prevent bowel cancer. This is most likely due to the fact that the drug is generally better known, which could be due to widespread media coverage of the benefits together with the fact that aspirin is an older drug.
The survey then asked GPs about their awareness of Lynch Syndrome and the role that aspirin can have in preventing cancers linked to the syndrome. People who have Lynch Syndrome (also known as HNPCC) have inherited a faulty version of a gene, which increases their chances of developing certain cancers including bowel cancer and womb cancer.
A trial we part-funded, called the CaPP2 trial, has shown a significant reduction in cases of bowel cancer among those with Lynch Syndrome by taking 600mg of aspirin a day.
But 600mg was the dose that GPs participating in our study reported as being least willing to prescribe, compared to lower doses of aspirin.
However, GPs who said they were aware of the preventive effects of aspirin for people with Lynch Syndrome reported being more willing to prescribe this higher dose.
How can we support GPs to use chemoprevention?
We think the preventative effects of tamoxifen and aspirin, and the associated national guideline for tamoxifen, need promoting more.
“Some centres are providing information on preventive therapy, but this is patchy,” says Smith. “To ensure all patients are able to make an informed decision – standardised information is needed.”
And there are ways to do this without reinventing the wheel.
For example, GPs in Scotland have access to a form that carries extra information about high-risk patients who are referred from secondary care (such as through breast cancer departments, family history and genetics clinics). This includes information about the specific dose that has been recommended, the time limits advised on taking tamoxifen and the advice the clinician had provided to the patient already.
There’s also a prescribing policy that’s already in place in Greater Manchester for tamoxifen and raloxifene (another preventative drug) that could be tested for the rest of England, Wales and Northern Ireland.
Cancer preventing drugs, used appropriately, have the potential to save many lives by stopping cancer developing in the first place.
And GPs across the UK should be given the support they need to make this happen.
Author: Helen Beck, policy research manager at Cancer Research UK
Source: Cancer Research UK - Science Blog
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