Incorrect: The radiation dose used in mammography is lower than the annual radiation dose we receive from the environment. The benefits of regular mammograms outweigh the potential risks associated with X-ray radiation.
FULL CLAIM: Mammograms don’t prevent cancer; mammogram contributes to cancer development because they expose breasts to x-rays and because of tissue damage
REVIEW
Breast cancer is a major public health concern. It is the second most common cancer among women in the U.S. and the second leading cause of death among them. The American Cancer Society estimates that more than 300,000 women in the U.S. will be newly diagnosed with invasive breast cancer in 2024 and that more than 40,000 will die from it. In Europe, breast cancer is the most commonly diagnosed cancer and the most common cancer cause of death among women.
In an effort to detect breast cancer at an early stage, the American Cancer Society began recommending annual mammograms in 1976, the idea being that early detection of cancer improves the odds of successful treatment.
However, naturopath Barbara O’Neill claimed that mammograms actually contribute to cancer rather than prevent it. In an interview posted on TikTok in May 2024, O’Neill was asked about mammograms and stated that “it’s pushed to prevent and it does not prevent”. She further added that repeated mammograms contribute to breast cancer because of the radiation sent through the breast and because of breast tissue damage that allegedly occurs during the test. This video generated 1.6 million views on TikTok at the time of writing. It was also posted on Facebook.
O’Neill holds no relevant health-related qualifications and has a track record of spreading health misinformation. The New South Wales Health Care Complaints Commission barred her from providing any health services, after finding that she had told patients cancer could be cured with sodium bicarbonate (baking soda) and promoted misleading advice on pregnancy and child-rearing.
However, O’Neill’s claim is inaccurate, as we will show below.
Mammograms don’t increase the risk of breast cancer
Traditional mammography works by compressing the breast between plates and sending X-rays through them. Areas of higher density in the breast appear white on the resulting image, just like bones appear white on a regular skeletal X-ray image.
The mammogram thus allows the detection of dense tissue in the breast that has an abnormal shape or unusual location. Denser areas may not be a tumor, but detecting them helps physicians decide whether to run additional tests like tissue biopsy.
Compressing the breast between the plates helps to immobilize the tissue and reduce blurring that can occur if the person moves during the X-ray. It also allows the use of a lower dose of radiation because it reduces the distance that the X-rays have to travel from one plate to the other.
Compressing the breast can generate discomfort, pain, and even bruising, which would signal small tissue damage. However, injuries to the breast don’t cause cancer, contrary to O’Neill’s claim. On that matter, the Canadian Cancer Society stated that:
“Compressing the breast during mammography does not cause breast cancer. Compression does not make tumours that are already there grow or spread any faster.”
X-rays are a form of ionizing radiation. This means that repeated exposure to high enough doses of X-rays may cause genetic mutations that may lead to cancer. However, the doses of X-rays used in mammography are low.
The American Cancer Society explains that the average dose of radiation for an annual mammogram is 0.4 millisieverts (a sievert is a unit of radiation dose received). For comparison, someone in the U.S. absorbs a dose of 3 millisieverts each year because of the radiation naturally present in the environment. This means that we are annually exposed to a radiation dose seven times higher than the dose used in mammograms.
Therefore, the American Cancer Society stated: “the benefits of mammography outweigh any possible harm from the radiation exposure.” Similarly, the U.S. National Institute of Biomedical Imaging and Bioengineering said:
“for most women, the benefits of regular mammograms outweigh the risks posed by this amount of radiation.”
Regular mammograms help reduce breast cancer mortality
O’Neill’s claim that mammograms don’t prevent cancer is also inaccurate. Indeed, regular screening allows early detection of cancer, and early diagnosis is associated with an increased chance of survival. According to Cancer Research UK, all women diagnosed at an early cancer stage will survive for at least five years. This statistic falls to three out of ten women if the diagnosis is made at a late cancer stage.
Scientific studies also showed that regular mammograms were associated with reduced breast cancer mortality. A randomized clinical trial followed women for more than twenty years in the U.K. and found that those who had yearly mammograms from age 40 to 48 years had a reduced breast cancer mortality over the following ten years compared to those who didn’t have yearly mammograms during their forties[1].
Another study compared breast cancer outcomes between women in Sweden who participated in breast cancer screening programs and women who didn’t. The study found that participating in the screening programs was associated with a 60% lower risk of dying from breast cancer within 10 years following diagnosis[2].
A study in the Netherlands reported that women who participated in mammogram screening programs received cancer diagnoses at an earlier stage than women who weren’t screened, and that these women had a better chance of survival[3]. Studies in Canada and Sweden also found that regular mammograms were associated with lower breast cancer mortality or longer survival[4,5].
However, it ought to be noted that some studies didn’t report meaningful benefits from regular screening in terms of reducing breast cancer mortality[6,7]. It’s possible that improvements in cancer treatments over the years tend to reduce the benefit of early cancer detection, as late-stage cancer becomes more treatable with more recent treatments[6].
Regular mammograms also come with some limitations, like overdiagnosis. This is the risk of detecting a tumor that would never have become symptomatic and progressed to cancer. Consequences of overdiagnosis include the patient suffering from unnecessary psychological distress or undergoing unnecessary treatments or surgical interventions.
If the positive impact of regular mammograms on cancer mortality were to diminish over time owing to better treatments while the risk of overdiagnosis remains the same, it might progressively shift the risk/benefit balance of screening programs[6].
That said, the American Cancer Society explained that overdiagnosis remains a relatively marginal risk:
“[O]verdiagnosis isn’t thought to happen very often. There’s a wide range of estimates of the percentage of breast cancers that might be overdiagnosed by mammography, but the most credible estimates range from 1% to 10%.”
Considering that scientific studies generally indicate that regular mammogram screening is associated with reduced breast cancer mortality, several medical organizations recommend the procedure. The American College of Obstetricians and Gynecologists recommends annual or biennial screening mammograms from 40 to 75 years of age for women who have an average risk of cancer. The American College of Radiology recommends annual screening mammograms starting at 40 years of age, while the American Cancer Society recommends a screening every year from age 45 to 54, followed by a screening every two years afterward. In Europe, the European Commission suggests biennial to triennial screening starting age 45 and strongly recommend a biennial screening starting age 50.
Conclusion
Periodic mammography screening doesn’t cause nor contribute to cancer growth, contrary to Barbara O’Neill’s claim. In fact, regular mammograms do the opposite. By allowing for early detection of cancer, mammograms improve the success of cancer treatment and increase the chance of survival.
REFERENCES
- 1 – Duffy et al. (2020) Effect of mammographic screening from age 40 years on breast cancer mortality (UK Age trial): final results of a randomised, controlled trial. The Lancet Oncology.
- 2 – Tabár et al. (2018) The incidence of fatal breast cancer measures the increased effectiveness of therapy in women participating in mammography screening. Cancer.
- 3 – Otto et al. (2012) Mammography Screening and Risk of Breast Cancer Death: A Population-Based Case–Control Study. Cancer Epidemiology, Biomarkers & Prevention.
- 4 – Duffy et al. (2020) Mammography screening reduces rates of advanced and fatal breast cancers: Results in 549,091 women. Cancer.
- 5 – Coldman et al. (2014) Pan-Canadian Study of Mammography Screening and Mortality from Breast Cancer. Journal of the national cancer institute.
- 6 – Christiansen et al. (2022) Change in effectiveness of mammography screening with decreasing breast cancer mortality: a population-based study. European Journal of Public Health.
- 7 – Miller et al. (2014) Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. The British Medical Journal.
