Commentary: Do earlier, annual mammograms save more lives?

PROVIDENCE, Rhode Island: Mainstream medical opinion holds that screening mammography is a lifesaving procedure. But doctors disagree over how often women should be screened for breast cancer. Last week, a panel of doctors known as the US Preventive Service Task Force revived the debate over mammographs by issuing a new recommendation. Their old guidelines advised starting at age 50 and getting screened every other year; the new ones keep the every-other-year recommendation but lower the starting age to 40.

Despite the new recommendations, many doctors will maintain that an annual mammogram is a necessity for me and every other woman over 40. But a growing faction warns screening healthy women this frequently might do more harm than good.

I haven’t chosen to get mammograms more than every other year - despite some protests from my doctors. The ideal schedule has to take into account the latest data on risks and benefits. Recent studies show that every-other-year screenings still catch tumours early enough for treatment. And annual screenings have been linked to false positives and unnecessary follow-up care, including biopsies and even surgery. 

TRADITION VS UPDATED EVIDENCE

The arguments represent part of a bigger debate in medicine that pits tradition against updated evidence, and calls into question the ethics of promoting tests or interventions that may not make a meaningful difference. In some cases, these tests or interventions may even have a small potential for harm. 

Screening proponents tend to favour hammering away at the simple message that the procedure “saves lives”, while sceptics advocate for more transparency about limitations and risks, and more freedom for patients to make their own informed decisions.

Some experts argue that we could benefit from more randomised controlled trials - and that the existing trials need to be analysed more critically. (None of this applies to people who have special risk factors such as the BRCA1 gene, and there’s no question mammography is an important diagnostic tool used when someone has found a lump.)

Rita Redberg, editor-in-chief of JAMA Internal Medicine and a professor of medicine at UC San Francisco, told me people tend to overestimate the benefits of screening and overlook the harms. Some trials do show a modest reduction in the number of deaths attributed to breast cancer, but not a reduction in deaths overall. 

That may happen because the overall effect is too small. Breast cancer causes just 2.5 per cent of deaths, and reducing that by 10 per cent or even 20 per cent might make too small a dent in overall deaths to show up in the studies.

I asked her if screening improves one’s quality of life as catching cancer early could help patients dodge debilitating chemotherapy or radical surgery. She said there’s no evidence for that. If anything, more screening leads to more surgery. 

MAMMOGRAPHY SCEPTICISM

Scepticism of screening mammography intensified a few years ago after some surprising studies showed that among women who get screened every year, most will get at least one false positive, and that many small cancers caught by mammography would never have metastasised or caused any health problem if ignored. 

The concept of non-threatening cancer is counterintuitive. To help, some researchers use an animal analogy. Some tumours are turtles, and aren’t going anywhere. Some highly malignant ones are birds, and they are getting out no matter what. Screening is only useful for those in the middle - rabbits. Tumours don’t come labelled, however, so doctors may order surgery for the turtles just in case. 

In a video created in response to the task force’s new guidelines, UC San Francisco medical professor Vinay Prasad pointed out that a 25-year randomised controlled trial, out of Canada, showed that for healthy, average-risk women, screening mammography did not save lives.

RISK OF RADIATION EXPOSURE

While Prasad dismissed the concern that mammography exposes women to small doses of carcinogenic radiation, Redberg isn’t ready to write that off. Some studies have estimated a small fraction of women who get regularly screened will get cancer from the radiation. Whether that’s an acceptable risk depends on the size of the benefits. 

Task force member John Wong, a professor of medicine at Tufts, explained to me that the change in the panel’s recommendations is based on a model, and over the past few years, a number of inputs have shifted. 

Those included a higher number of detected cancers among women in their 40s, better screening technology, better treatments and persistent health disparities - Black women are more likely to get breast cancer and die from the disease, for reasons that scientists have yet to pinpoint. He thinks the benefits of screening mammography are so clear, it’s unethical to do more randomised trials.

But he also admits that we don’t know why more women in their 40s are getting diagnosed with cancer. Are deadlier cancers striking this age group? Or are more turtles being discovered because, no matter what the official guidelines are, many doctors push women in their 40s to get screened? It’s also unclear whether more screening will do anything to improve racial disparities. 

Wong asked me if he’d convinced me. I am convinced that there’s a need to balance harms and benefits, and I had already used the panel’s earlier recommendation - every other year starting at 50 - to guide my own schedule. But I disagree that it’s unethical to conduct more clinical trials. If he wants to start one, he can sign me up.