New study on screening mammography shows more harms than benefits

13 July 2020

A study published on June 23 2020 in JAMA Network Open, one of the journals of the American Medical Association, adds to the growing body of literature demonstrating that screening mammography programs fail to deliver on their promise of saving lives, and are instead an expensive waste of time and both human and medical resources.

Screening mammography is a procedure in which women who have no signs or symptoms of breast cancer undergo low-energy X-rays of their breasts. Its stated goal is to detect breast cancer at an early stage, at which it will be more easily treatable and hopefully, completely curable – hence the slogan “Early detection is your best protection.”

The most important metric of success of a screening mammography program, therefore, would be a decline in the percentage of breast cancer patients diagnosed at a late stage, when the cancer has already started to spread throughout the body. (Keep in mind that people with breast cancer do not die of tumours in their breasts; they die of metastases – breakaway tumours that invade vital organs.)

Evidence against screening mammography has been accumulating for decades, as I discussed in my previous article Breast cancer screening – when ‘talking to your doctor’ may mislead rather than inform.

The new study, Assessment of Breast Cancer Mortality Trends Associated With Mammographic Screening and Adjuvant Therapy From 1986 to 2013 in the State of Victoria, Australia, is an persuasive addition to this evidence, specific to the Australian context of breast cancer incidence, treatment and mortality.

Given that Australia now has the third highest age-standardised incidence rate of breast cancer in the world, after Europe and North America, the question of whether screening mammography programs are effective is a critical one to answer.

Before diving into the findings of this article, a few definitions and some background on screening mammography programs will be helpful:

• Early breast cancer (EBC): Breast cancer confined to the breast and adjacent axilla (armpit). This correlates to stages I and II breast cancer, as defined by the American Joint Cancer Commission (AJCC).
• Advanced breast cancer: Breast cancer that has invaded tissues and organs other than the breast and adjacent axilla, correlating with AJCC stages III and IV breast cancer.
• Adjuvant therapy: Cytotoxic chemotherapy and endocrine therapy (hormone blocking medications), administered after surgical removal of the breast tumour in order to reduce the risk of cancer recurrence.
• Downstaging: Reduced incidence of advanced breast cancer in comparison to early breast cancer.
• Incidence: The number of cases of an event, in this case diagnosis with breast cancer, occurring in a particular population during a given period.
• Mortality rate: The number of deaths (in this case, from breast cancer) in a particular population, scaled to the size of that population, per unit of time.

The federally-funded BreastScreen program was commenced in 1991. By 1995, 30% or more of Victorian women aged 40 years or older were screened. By the late 1990s, 53-57% of Victorian women aged 50 to 69 years who were invited to participate showed up for an initial free screening mammogram, with 60% of those returning for a second mammogram 2 years later, and 80% of those returning for third and subsequent mammograms.

In addition, between 5 and 10% of Victorian women undergo screening mammography outside the BreastScreen program.

Now, onto the new study’s findings.

Firstly, while the incidence of breast cancer in Victoria has risen in the last few decades, the breast cancer mortality rate dropped about 30% between 1994 and 2013, the last year of data analysis.

That’s good news for women, but should breast screening programs get the credit? Not so fast. Take a look at the figure below, which separates out total breast cancer diagnoses into the stage at which they were diagnosed.

Note the steep increase in early breast cancer diagnoses (stages I and II) that occurred after 1990. There was a 62% increase in the crude (non-age-adjusted) incidence of stage I breast cancer from 1990 to 1995, while the incidence of stage II breast cancer more than doubled.

These increases in early breast cancer incidence are evidence of overdiagnosis – the detection by screening mammography of breast tumours that would never have caused symptoms or death during a patient’s ordinarily expected lifetime.

Overdiagnosis of breast cancer results in a raft of harms including unnecessary and mutilating surgery, exposure to hazardous chemotherapy drugs and radiation therapy, immense psychological suffering, and potential medicolegal repercussions including impacts on health and life insurance premiums.

This lecture by Dr H. Gilbert Welch is an excellent exposition of the dangers of diagnosis:

Now take a look at the line representing advanced breast cancer diagnoses (stages III and IV). Remember, if screening mammography does what its advocates tell us it does, the incidence of advanced breast cancer will drop as more and more women participate in screening programs. However,

That’s right – not only did the BreastScreen program and other screening mammography services in Victoria fail to detect breast cancers at an early stage when they are more treatable, the rate of diagnosis of advanced breast cancer has almost doubled since screening mammography was introduced.

The authors point out that previous research in the US, Netherlands, Norway and New South Wales had shown no decrease in the incidence of advanced breast cancer after screening mammography programs were introduced. Advanced breast cancer incidence either remained stable or went up in these 4 regions.

In fact, the age-standardised incidence of advanced metastatic breast cancer for women in NSW increased by 67% from the 1988-1995 to the 2006-2012 periods, providing clear evidence that mammographic screening was not downstaging breast cancer in that state.

So why are fewer women dying of breast cancer? The authors of the study argue that better treatment – namely, higher uptake of adjuvant therapy – should be given the credit.

Their conclusion does not beat around the bush:

Women should not be sold a false bill of goods about screening mammography. It is more likely to cause harm than benefit. How much harm?

The rate of overdiagnosis in the NSW BreastScreen program was previously estimated to be between 30 and 42%, depending on the method used.

The authors of the just-published study used the more conservative estimate of a 30% overdiagnosis rate to calculate that the ratio of harm (overdiagnosis) to benefit (avoidance of breast cancer death) was 15:1 – that is, 15 women harmed for every woman whose life is saved.

So what should women do if they are worried about breast cancer, and reduce their risk? As I mentioned in my previous article, Cancer prevention and treatment, research shows that practising just 5 habits can lower a woman’s risk of breast cancer by 30%:

• Don’t smoke
• Drink very little or no alcohol
• Maintain a healthy body weight
• Don’t use HRT
• Walk 30 minutes per day.

Please share this important information with everyone you know, and if you need personalised help with developing a cancer prevention (or recurrence prevention) plan that you can stick to, apply for a Roadmap to Optimal Health consultation today.