Interview with Dr. Shelia Hoar Zahm, Sc.D, National Cancer Institute (NCI) Scientist


Shelia Zahm, with a doctorate of science in epidemiology from Harvard, is Dr. Blair’s protégée, though herself recently retired, and one of a pair of researchers responsible for crucial research, work that was very important to us in our search for answers when Katherine was first diagnosed.  As with Dr. Blair, I am struck by her generosity.  Why should she take time out of her busy day to speak with me?  Perhaps because she cares about educating the public about all she has learned in the many years she has worked at the National Cancer Institute, first as researcher, then as Deputy Director of the Division of Cancer Epidemiology and Genetics.  As Deputy Director, she was able to influence and facilitate research in many different areas of cancer research, and she is proud of that.  Both she and Dr. Blair have impressive resumés, but you would grasp within five minutes how knowledgeable they are, just by talking with them.  She says of her mentor, “he’s wonderful, just wonderful.”  And I get the sense the feeling is mutual.

Dr. Zahm was drawn to this area because of her personal history.  “I was always interested in health since I had family members who were ill.  I was interested in causes, and I was interested in math.  And I discovered that epidemiology combined my love of biology and math and helped answer questions about cause of disease.  I knew that if we identified causes, we could help prevent diseases.  I have chronic lymphocytic leukemia myself, and I am so glad people are working on treatments.”  She repeats this.  “But if we could identify causes and prevent disease, that would be better than having them treated.  My father was sick for much of my childhood, and my mother developed and eventually died from breast cancer. When I was in graduate school, the epidemiology department focused on cancer.”  How much this wish echoes the experience of every cancer survivor, every bereft relative of someone lost to cancer: to prevent the disease to start with.  And yet so little attention is paid to prevention in the United States. 

Dr. Zahm draws an analogy to a two by two table, which is often used in epidemiology, usually to compare exposure on one side and disease on the other.  So, for example, here is a two by two table for smoking and lung cancer:



Lung Cancer

No Lung Cancer







Each square would have a different number of people in each category.  What you expect now – after all the decades of research on this topic – is higher proportions of lung cancer in smokers.  Epidemiologists habitually use tables like these to help them think about and design experiments.  Dr. Zahm’s analogy constructs a different kind of two by two table, with voluntary vs. involuntary on one side, and preventable vs. non-preventable on the other side.  Tobacco is voluntary and preventable (1).  Occupational exposures are involuntary and preventable (3).  Genetics are non-preventable and non-voluntary (4).  There’s not much you can do about your genes, after all.  For voluntary and not preventable (2), it’s harder to find examples, Dr. Zahm says.  Reproductive factors might be one.  Or the nuns with higher risk of breast cancer because they have not given birth or breastfed, I add.  “The cell that is voluntary and preventable (1) should be a high public health priority.  That’s why I like the idea of working on occupational environmental health.”




Not Preventable







This concept is so useful.  There are other implications to this two by two cell.  The cell that is voluntary and preventable should be a high priority because people can make choices and avoid exposures.  But in some ways, the involuntary and preventable (3) exposures are morally worse.  And there is some blurring between these categories.  Consider, too, voluntary vs. involuntary.  Sometimes, people sign up for these exposures, as with lawn chemicals, or hair dye.  But sometimes pesticides are sprayed right in a window at night, without permission or notification.  Or a neighbor burns garbage, releasing dioxin into the neighborhood.  Or PCBs are dumped into the water supply.  Or a variety of carcinogens are released into the air by chemical plants, both legally and illegally.  And that, in my opinion, is not only unfortunate and preventable: it is morally criminal.  Perhaps society prefers to think that certain things are in the non-preventable column because we do not wish to accept the work or cost needed to move them to preventable.  People get used to high cancer rates and begin to think of it as unpreventable.  They accept these deaths. 

I ask Dr. Zahm the question about the anxiety surrounding the subject of cancer and whether this has bothered her over the years. 

It’s interesting.  When I first started working in the field, I had to pick a doctor within the school HMO, and I ended up choosing an oncologist.  When I first went to her, she asked me why I had chosen an oncologist when I did not have cancer.  I told her that I was studying cancer, and I really wanted someone who would be looking for it.  My doctor admitted that every few months she would go to her own physician and asked to be checked out from top to bottom.  It’s the medical school disease, you know?  There was always a sense that this wasn’t just an academic exercise.  The diseases we were studying are terrible diseases, and every case, even if it was rare, was a terrible tragedy.  We are very aware.

This isn’t just the disease of medical students – to be worried about all the things that can happen, to have lost the protective denial that bad things won’t happen to us.  This phenomenon also afflicts cancer survivors – those who have had cancer and those who have lost someone.  I want to frame Dr. Zahm’s words: “this wasn’t just an academic exercise….”  When Katherine was in the hospital, our doctors had a poster on the door with pictures of bald little kids hooked up to IVs and a motto that said “Remember: this isn’t routine for us….”  It is easy enough for doctors and researchers to fall into routine, to distance themselves from the tremendous burden of really knowing other people’s suffering.  But the best ones never do.  The best ones always know that each case is a terrible tragedy. 

I find as we talk that this is a person I can trust…and have trusted all along through her research.  I am not surprised to find her a genuine, warm person.  I am not surprised to learn that someone she has loved has suffered from cancer.  I have met with this sense of responsibility in the greater part of the scientific literature; it comes across even through the otherwise dry, impartial language of science.  I just wish we were justified in placing an equal amount of trust in those bureaucrats and politicians in charge of the regulatory apparatus, who make decisions about what to do with this information and who control who is exposed, where, when, and how much.  But it is up to us to keep them responsible.  If we do not complain to regulatory agencies and politicians, if we do not protest against this terrible injustice, the industry will continue to have its way, and we will be partly to blame if they do.

Zahm sees shortcomings in our regulatory system.  It’s not that she’s asking for a complete ban on all dangerous chemicals.  She recognizes that “there are costs and benefits… we don’t want cholera, so we put chemicals in water.  There may be something else we could use, but it’s more expensive.  Costs are important as well.   But what I hope is that research will show us which pesticides we need to stop using, which we could use safely with changes in the way we use them.  We need to be much more aware of when chemicals are sprayed and under what conditions.”  I bring up the subject of cosmetic pesticides.  She laughs and agrees: “green grass, green weeds….  I’m not that picky about what is green in my yard.  That is the sort of thing we can do away with.  Do we need to apply chemicals on an area where children are going to be playing?”  Zahm tells the story of being in meetings with regulators.  “At one meeting – Aaron Blair and I were talking to staff from EPA and other scientists.  And one man said to us, ‘Wait – you’re telling me chemicals we’re actually using could be causing problems?’  It had never occurred to him before that products on the market could be causing cancer.”  Astonishing.  This is comparable to a moment in the documentary Tapped, about the bottled water industry, where an FDA expert testifying about BPA is dumbstruck under questioning about the legitimacy of using only industry research to certify safety.  It had never occurred to them that they should not just rely on studies produced by the industry (Tapped).  The questioner, John Kerry, calls this a disgrace.  Yet this continues to be the standard.  The regulators seem not to intend to fail at their jobs, yet all they can hear is the tune of the poison pied piper: the steady stream of advertising, lobbying, and bullying tactics that industry routinely employs.  Some scientists are insulated from some of this, but in an effort to maintain their objectivity and scientific caution, they sometimes hold back too much, as Dr. Blair has said.  They also know that if they are wrong in taking off the market a chemical that turns out to cause no harm, industry will never let them forget it.  Of course, that is very unlikely, considering how few chemicals are ever refused. 

Dr. Zahm has a list of reforms she would enact if she could somehow, magically, be put in charge of regulating chemicals in this country.  I wish she could.

I think the most important thing is to change the burden of proof.  Things should be proven to be safe before they are introduced rather than waiting to find they are harmful after the horse is out of the barn.  There were so many chemicals that were grandfathered in when toxic substances were regulated in this country, and they’ve never gone back and researched the chemicals.  We should also change access to information.   For example, pesticide companies only have to reveal “active” ingredients, meaning those with pesticidal activity.  Many of the other ingredients in pesticide formulations are not biologically inert, but they are not considered a pesticide, so they don’t have to be listed.  That information is protected, proprietary.  The information needs to be public for research on safety.

Regulators also need to increase consideration of exposures across the lifetime, not just consider exposure as adults.  We need to know what happens if one is exposed prenatally, in childhood, at menarche, before the first birth, during pregnancy, etc., across the lifespan.  We should conduct animal and in vitro testing taking into account populations that have special susceptibility, like children and those with impaired immune systems.  Regulators need to think of the exposures and susceptibilities of the most vulnerable populations, not just the “average adult” in testing.  

Historically, most carcinogen testing was designed to identify direct carcinogens.   What if the substance just changes immune function, and that changes the ability to fight disease?  Will the testing regimens detect those changes? In general, the regulatory system has been designed using data from animal studies.  The agencies don’t really know what to do with epidemiological studies.  Often the exposure assessment may not be detailed enough to use in the risk assessment models the agencies use, and there is often concern about confounding or other bias.  If the human studies are positive, but animal studies are not, usually nothing happens. 

The US regulatory landscape also needs more post-marketing monitoring particularly for drugs but other newly introduced compounds as well. Without well-designed follow-up studies, we can miss detecting modest increases in common outcomes.  An “alert clinician” may notice an extremely unusual outcome caused by an exposure, but cannot detect a small increase in a common disease. 

Dr. Zahm’s final message to parents is simple:We need to focus on what we can do – the expression I have heard is prudent avoidance.  In the absence of knowledge about the safety of something, we have to be careful.   Most people inherently understand what prudent avoidance is.  For example, when someone is pregnant, they are typically more careful of things they wouldn’t otherwise think twice about, even in the absence of data about a possible hazard.  They are being prudent.  In general, we need to be more careful.”