The Ethics of Screening Mammography

How data, risk stratification, and genetic signatures might change our calculus

I appreciate this essay for its reframing of our debates about cancer screening; viewing them through an ethical lens. The speculation that we might eventually be able to identify individuals harmed by radiographic screening and how this would alter our approach is both intriguing and alarming.

Adam Cifu

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The value of breast cancer screening with mammography is increasingly being questioned. Women are trying to decide what is right for them and the USPSTF is trying to decide what is worthy of reimbursement. Currently, the medical literature is at a stalemate.[1]¹ When faced with a dilemma, it is sometimes helpful to look at the issue from a fresh perspective. This essay reviews the current tension around screening mammography from an ethical perspective and offers some steps for the future. 

Background

Screening mammography uses ionizing radiation, a known carcinogen. The dose of radiation in each exam is very low, but exposure is cumulative. Also, the absorbed dose varies with the density of the breast. Women with more glandular tissue receive a higher exposure. Thus, over decades of screening, radiation exposure may not be trivial, particularly in women with extremely dense breasts. 

Across a population there is some percentage of breast cancers which are caused by screening mammography. The exact number is the subject of debate and not well studied. One article from 2011 approximates 86 cancers and 11 deaths per 100,000 women due to breast cancer screening. Another paper estimates 20-25 fatalities for 100,000 women screened starting at age 40. Due to lack of data, and ethical limitations in obtaining more data, we do not know how many breast cancers are caused by screening. 

Medical physicists take the following stance:

“Given the lack of scientific consensus about potential risks from low doses of radiation, predictions of hypothetical cancer incidence and mortality from the use of diagnostic imaging are highly speculative. The AAPM, and other radiation protection organizations, specifically discourages these predictions of hypothetical harm. Such predictions can lead to sensationalistic stories in the public media. This may lead some patients to fear or refuse safe and appropriate medical imaging, to the detriment of the patient.”

We understand screening as a ratio of harm to benefit. Mammographers justify carcinogenic risk to women through the ethical principal of utilitarianism, claiming cancers caused by radiation are justified by the number of lives saved. Unfortunately, the exact number of lives saved is unknown and it is generally accepted that over the past decades screening has had a diminishing effect given the improving treatment options for patients with cancer. Today, the harm/benefit ratio for mammography is a ratio of an unknown numerator to an unknown, but shrinking, denominator. 

An alternative to utilitarianism is deontology, an ethical perspective which uses rules to guide practice such as “First, do no harm.” Informed consent is another pillar of ethics that allows patients to decide for themselves what is best. Let’s put the ethical tools of utilitarianism, deontology, and informed consent to work. 

The Classic Trolley Problem Applied

The trolley problem is a commonly discussed ethical dilemma that can be used to illustrate the current ethical state of breast cancer screening. The trolley problem:

There is a runaway trolley barreling down the tracks. Ahead, on the tracks, there are five people tied up and unable to move. The trolley is headed straight for them. You are standing some distance off in the train yard, next to a lever. If you pull this lever, the trolley will switch to a different set of tracks. However, you notice that there is one person on the sidetrack. You have two (and only two) options:

1. Do nothing, in which case the trolley will kill the five people on the main track.

2. Pull the lever, diverting the trolley onto the sidetrack where it will kill one person.

Which is the more ethical option? Or, more simply: What is the right thing to do?

When posed this problem, most people pull the switch, killing the one person to save five. This behavior mimics mammographers’ utilitarianism, sacrificing one in the belief that they are saving many more. The killing of an individual is made easier when the victim is anonymous and physically distant from us.

The trolley problem can be modified to what is known as the “footbridge problem” where the decision maker must personally push a victim off a bridge to stop a train from hitting a crowd. With this modification people become reluctant to make a similar decision due to the increased agency from physically pushing the victim. Psychologists refer to this changing agency as “editing” vs. “authoring”. Furthermore, the decision to push someone off a bridge becomes increasingly difficult when specific traits of the victim are known.

The application of deontological rules enables an individual to do nothing and still do the right thing. Deciding to not author a death is a rational and ethical decision. Deontological ethics also circumvent higher level “moral calculus” within our brains and allow for decisions free of errors from cognitive (financial) biases and emotions. 

Ethical Dilemmas Scaled to Screening Mammography

Today, we get away with using a carcinogenic probe to screen genetically fragile tissues for cancer because the victims of radiation induced breast cancer are anonymous. It is a trolley problem. This may not remain true. There is early human evidence that radiation induced cancers can have distinctive genetic mutations. Women with radiation induced cancers would also have decades of past mammography. It is possible that we will eventually be able to identify the individual women affected by mammographically induced breast cancer. This would change the trolley problem into a footbridge problem.

If we believe Drs. Prasad and Jørgensen that the denominator of the harm/benefit ratio of mammography is shrinking, then the ratio is dominated by the numerator. If a patient’s risk of injury from breast cancer screening is not zero, they should be informed of the risks and alternatives -- delaying or deferring screening. There is little informed consent in today’s breast imaging centers. A recent study informing women with a “decision aid” concluded that low-risk, informed women tended to delay screening and many women found the information “surprising”. This study did not include information on radiation risks.

Furthermore, because we know that breast cancer incidence increases with breast tissue density and density increases radiation exposure, we need to evaluate whether this relationship is causal. Answering this question would begin with a retrospective study examining the exposure of women with cancer to mammography over decades.

Currently, the value of screening is based on the incidence of the disease in the general population, but could we personalize screening protocols? Finding high-risk women who may desire extra surveillance or risk reducing surgery is relatively inexpensive when compared to the cost of annual mammography over 30-40 years. Once these women are excluded from the general population, the remaining cohort may have little or no need for screening. The industry has yet to study this issue.

Conclusion

A more balanced approach between utilitarianism and non-maleficence is needed among mammographers. A world where discovery of radiation induced cancers becomes possible may change practice behaviors. Pathological specimens sitting in hospitals today may pose a medico-legal risk tomorrow. Young physicians considering a breast imaging fellowship need to be informed of a future where the trolley problem becomes a footbridge problem. Speculating about the medico legal implications of discovering women harmed by screening means that the industry should begin discussing a potential black swan event. A class action settlement on par with smoking, talcum powder, or asbestos is not inconceivable.

Seth M. Hardy, MD MBA is an Associate Professor at Penn State University and continues to survive on a Phase II leukemia trial at our flagship National Cancer Institute. He is currently trying to recruit triple negative breast cancer patients into a novel imaging trial at Penn State.

1. A cynic might suggest that where you stand in this stalemate depends of whether or not you have financial skin in an estimated $4.4 billion marketplace. 

Photograph by Amogh Manjunath