A radiologist checks mammograms for breast cancer in Los Angeles. Canadian guidelines recommend that women ages 50 to 75 at average risk of breast cancer should undergo systemic screening every two to three years.Damian Dovarganes/The Associated Press
What’s the best age to start mammography screening for breast cancer – 40, or 50? Maybe 45?
We’ve been arguing about that since the first screening program launched in B.C. in 1988.
It’s actually a complex, emotion-laden question with inadequate data, and so a definitive pronouncement evades us. And there’s no right answer other than “it depends.”
The Canadian Task Force on Preventive Health Care (CTFPHC) got that part right in its most recent recommendations when it said: “Breast cancer screening is a personal choice.”
But to make a reasoned personal choice, you need good personalized information. And that’s the rub. We don’t have great cancer data, and what we have is largely inaccessible to the public.
When are Canadians eligible for breast cancer screenings? Guidelines for each province and territory
Canadian guidelines recommend that women ages 50 to 75 at average risk of breast cancer should undergo systemic screening every two to three years. The task force says earlier screening should be reserved for those with a personal or family history of breast cancer, those with genetic mutations like BRCA, or symptoms suggestive of breast cancer.
The CTFPHC guidelines have outraged many cancer researchers, clinicians and advocates, who want routine screening to begin at 40.
There is a well-worn mantra that “screening saves lives,” which is backed by many an anecdotal tale.
But screening has not lived up to its initial promise. When massive screening programs were created in the late 1980s and early 1990s, there was a belief that, caught early, most cancer could be treated and cured.
The reality is more humbling. In 2024, an estimated 30,500 Canadian women will be diagnosed with breast cancer, and 5,500 will die.
The good news is that breast cancer mortality has fallen sharply, with 21.8 deaths per 100,000 population today, compared to 41.7 in 1989.
But it’s not clear how much of that sharp reduction is because of screening. Declines in mortality rates are similar in countries with little or no routine screening. Most progress is probably the result of greater awareness, prevention measures (like big drops in smoking rates), and much-improved treatments.
We also have to be careful to distinguish mammography screening (the testing of women with no symptoms) from diagnostic mammography after a potential issue is detected, such as a lump or unusual discharge. Thankfully, women no longer show up to physicians’ offices with grapefruit-sized tumours.
The decrease in mortality owing strictly to mass screening is modest, especially in younger women. (Data show that screening is most effective for women ages 60 to 69; the risk of breast cancer increases after menopause.)
The task force cites these comparative data for its recommendation that screening women under age 50 at normal risk provides little benefit:
- Among 1,000 women who are not screened, 17 will be diagnosed with breast cancer and, over the next 10 years, two will die and 15 will not die;
- Among 1,000 women who are screened, 19 will be diagnosed with breast cancer, and one or two will die over the next 10 years. But 368 of those women will undergo more testing, including 55 who receive biopsies, and two who will be treated unnecessarily.
In other words, for every 1,000 women screened for a decade, one death will be prevented, theoretically.
There are 2.6 million women aged 40 to 49 in Canada, so prevented deaths can add up. Not to mention that no one wants to be the preventable breast cancer case that was missed.
Ultimately, as the task force says, the decision to be screened for breast cancer should be guided by a woman’s values and preferences.
Everyone’s risk is different, and so is their risk tolerance.
Still, mass screening is costly and inefficient. Routine screening misses the most aggressive and deadliest cancers. It also misses many of the women at highest risk, who are on the margins of the health system. Nor will screening address the issue of increasing rates of breast cancer in younger women in their 20s and 30s.
Self-referral can be empowering, but also inequitable: Consider that the highest uptake for screening is among white women at average risk.
The future of screening should be personalized, with screening schedules based on risk factors such as age, race, genetics, breast density, health history and lifestyle.
Instead of the endless debate about the age at which screening begins, we should be focusing on how to improve and target screening and other forms of cancer detection.
Resources are not unlimited, so we have to use our cancer dollars wisely, especially focusing on preventing cancer in the first place rather than just finding tumours and treating them.