Publication of Canadian recommendations

The Canadian Task Force on Preventive Health Care (Canadian Task Force) was established by the Public Health Agency of Canada (PHAC) to develop clinical practice guidelines to support primary health care providers in the delivery of preventive health care.

Recommendations of the Canadian Mammography Screening Group
Summary, by age group:

For women aged 40 to 49, based on the current evidence (trials, observational studies, modelling and a review on values and preferences), we suggest not to systematically screen with mammography. Because individual values and preferences may differ, those who want to be screened after being informed of the benefits and harms should be offered screening every 2 to 3 years (conditional recommendation, very low certainty.

For women aged 50 to 74, based on the current evidence (trials, observational studies modelling and a review on values and preferences), we suggest screening with mammography every 2 to 3 years. Because individual values and preferences may differ, it is important that women aged 50 to 74 have information about the benefits and harms of screening to make their decision (conditional recommendation, very low certainty).

For women aged 75 and above, based on the current evidence (observational studies and modelling; no trials available), we suggest not to screen with mammography (conditional recommendation, very low certainty).

Decision-making tools

Previous US recommendations had been much talked about and disputed, because they advocated starting screening at the age of 40, not for scientific reasons but for reasons of racial equity, since black women are at risk and have a higher incidence of breast cancer. However, there is no data to support the relevance of starting this potentially harmful mammography screening in younger women. The solution for these groups of women, who are unfortunately more exposed to the disease, does not lie in increased screening.
We reported on these new recommendations in the USA and the accompanying debate here: https://cancer-rose.fr/en/2023/09/17/lowering-the-age-of-screening-a-pandoras-box/
The Canadian guidelines are based on a systematic analysis of scientific evidence. They are more cautious and above all advocate an informed choice by women, after they have been informed of the risks of mammography screening, which are now known.

Recommendations based on personal choice

Based on an article by M. Larkin, summarised and translated by Cancer Rose

What methods were used?

According to new guidelines from the Canadian Task Force on Preventive Health Care, the potential harms and benefits must be carefully weighed up before women and their doctors decide to do breast cancer screening.

The draft guidelines are based on a review of more than 165 recent randomized controlled trials, observational studies, mathematical models and other data. The guideline working group included four breast cancer experts (a medical oncologist, a radiation oncologist, a surgical oncologist and a radiologist), three patient partners, six family physicians, a nurse practitioner, evidence review teams and other experts. To avoid potential conflicts of interest, oncologists provided input but did not vote on the final recommendations, Guylène Thériault, a family physician and chair of the breast cancer task force and working group, told Medscape Medical News.

The guidelines recommend that, after considering the potential benefits and harms of screening and informing women, mammography every two to three years remains available to women aged 40 to 74 with no increased risk.

Women with a significant personal or family history of breast cancer or genetic mutations that would increase the risk of breast cancer, those with symptoms such as a lump, those who believe they are at high risk and those who are transgender women should consult a healthcare provider about appropriate options, according to the updated guidelines, which do not apply to these patients.

The draft guidelines were published online on May 30 and are open for public comment until August 30.

Three main questions asked

In developing the guidelines, the working group asked itself ‘three main questions’, explained Guylène Thériault, a family doctor and chair of the study group and the breast cancer working group.

The first concerned the effectiveness of breast cancer screening in women aged 40 and over. For this question, this systematic review, unlike the 2018 guideline update, included not only randomised trials but also data from observational studies to ensure that the working group considered all available data.

The second question was about comparative effectiveness, i.e. looking at what happens if we start screening patients at age 40? Or at 50? What happens if we stop screening at the age of 74? Or if we use different tests, such as 3D mammography versus digital mammography?
The working group used the evidence found by the USPSTF after classifying it according to its own criteria. The results are similar, as are the recommendations in this area. ‘For example, we do not recommend additional screening for women with dense breasts because there are no studies to determine the benefit to patients.’ explains Dr Thériault.

The third question concerned women’s values and preferences when it comes to breast cancer screening, an aspect that the US did not examine. ‘We had examined this question in 2018, and this time, even though we broadened the type of studies, we received the same message: There are differences between women in their 40s and those aged 50 and over.’
‘The majority of women in their forties think that the disadvantages outweigh the advantages and are not interested in screening,’ said Ms Thériault. ‘But when I say the majority, I don’t mean all women. So we had to recognise that there is some variability. The majority of women aged between 50 and 74, but not all, think that the advantages outweigh the disadvantages. That’s why we say in our recommendation that between the ages of 40 and 74, it’s a personal choice’.

The objections

Not surprisingly, the working group heard objections to its draft guidelines. The first is that women aged 40 to 49 are being denied mammograms, said Michelle Nadler, a medical oncologist at the Princess Margaret Cancer Centre in Toronto, Ontario, Canada. ‘This [objection] has been highly publicised, which is unfortunate, because people who haven’t read the guidelines may believe it’s true,’ she said. ‘The guidelines clearly state that an eligible and informed woman in this age group who wants a screening mammogram should have it.’

The second objection frequently heard is that the working group overestimates the disadvantages of screening, such as anxiety and overdiagnosis, she said. But the ‘anxiety’ outcome was not taken into account in the guideline. Overdiagnosis was calculated on the basis of the literature, and the estimates were converted to a common denominator so that they could be compared, Nadler said. The same applies to benefits.

Another objection is that screening could reduce the need for chemotherapy or complete axillary dissection, Nadler said.
But the task force found no primary studies evaluating these outcomes.

Critics also said the recommendations did not take racial or ethnic variations into account. While more research is probably needed in this area, ‘the task force states that individuals should be informed of all their risk factors for breast cancer, including their race/ethnicity, and that this should be taken into account in screening decisions,’ Nadler said.

‘I was very surprised that some parties accused the task force of paternalism,’ added René Wittmer, MD, assistant professor of family medicine at the Université de Montréal and president of Choosing Wisely Quebec, Montreal, Quebec, Canada.
‘In my opinion, the emphasis they place on shared decision-making runs counter to medical paternalism and aims to empower women to make a decision that reflects their values and preferences.’

Decision aids, or ‘decision support tools’

Once the guidelines have been finalised, decision aids will be made available to patients and healthcare providers to help guide discussions about screening,’ said Nadler, an oncologist in Ontario.
‘Primary care providers need to know a person’s personal risk factors for breast cancer to know whether they have an average, above average or high lifetime risk of breast cancer. These guidelines do not apply to people whose lifetime risk of breast cancer is greater than 20%.
‘Risk communication standards are absolute numbers on a common denominator*’, she pointed out. ‘This is how primary care providers approach other important topics such as smoking cessation, cardiovascular disease (and decisions about statin drugs) and osteoporosis risk. The same standards should apply to breast cancer screening.
*This means that, for a better understanding of the results, we should endeavour to present them in the form of ‘real people’ represented, in a visual with dots (each dot being a person), within a group of individuals who represent the denominator. This group of individuals on which each result is represented must have the same number for those screened and those not screened, in order to facilitate comparison for the patient who wishes to be informed and understand. For example: X false alarms out of 1000 people.

In addition, she adds: ‘Healthcare providers should be aware that people from marginalised communities may benefit from several interviews until they are able to make a decision about screening that is appropriate for them’.

‘There is strong evidence that most of the progress we have seen in breast cancer outcomes (i.e. reductions in breast cancer mortality) is probably due to improvements in treatment, not screening,’ said René Wittmer. ‘In fact, reductions in mortality are observed even in age groups or countries where there is no systematic screening. This means that women benefit from advances in treatment, whether they choose to be screened or not’.

Related article: https://cancer-rose.fr/en/2024/06/08/reaction-to-canadian-screening-recommendations/

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