Breast Cancer & Pesticides in 1991
When Living on Earth first began 20 years ago, some new studies had emerged suggesting that breast cancer may be linked to pesticides such as DDT. Reporter Tatiana Schreiber produced a documentary for LOE on the issue and one of the researchers she interviewed was Dr. Mary Wolff of Mount Sinai School of Medicine. Host Steve Curwood catches up with Dr. Wolff to find out what has been learned since the controversial results of her early research.
CURWOOD: It’s Living on Earth, I'm Steve Curwood.
GELLERMAN: And I'm Bruce Gellerman. In the United States, one woman in eight can expect to get breast cancer - a higher rate than any previous generation. Only half the cases can be attributed to known risks factors such as genetics, so researchers have been investigating environmental exposure to get more answers.
CURWOOD: Back in 1991, when Living on Earth began, only a few scientists were looking at whether pesticides and other environmental toxins might play a role in breast cancer. A pioneering study at the time had found breast cancer incidence declined in Israel after the pesticides lindane and DDT were banned from dairy production in 1978.
One of our early shows explored the link between these chemicals and breast cancer. In a few minutes, we'll check in with one of those scientists we spoke with back then - but first, here's an excerpt from our 1991 story by reporter Tatiana Schreiber.
SCHREIBER: What's needed, scientists say, are studies that directly measure chemical residues in women who have breast cancer compared with those who don’t. One researcher who has done just this is Dr. Mary Wolff, a chemist at New York’s Mount Sinai School of Medicine.
Wolff recently completed a pilot study with Dr. Frank Falck at Hartford Hospital in Connecticut. Their report will be published later this year in the Archives of Environmental Health. She used techniques developed over years of studying how the body stores chemicals to measure pesticide residues in breast fat.
WOLFF: This was a case-controlled study of a small number of women, in which we measured a number of pesticide residues and found that some of them were elevated in cases with malignant compared with non-malignant disease.
SCHREIBER: The study involved 25 women with breast cancer and an equal number who had biopsies but didn’t have cancer. The results showed differences significant enough to interest the government’s National Institute for Environmental Health Sciences, which will fund a larger study – a collaboration between Wolff at Mt. Sinai and Dr. Paolo Toniolo, an epidemiologist at New York University’s School of Medicine.
Wolff and Toniolo will be looking at DDE, which is a metabolite of the pesticide DDT, and PCBs, a common industrial chemical - both in the organochlorine class of chemicals. They were found at higher levels among the women with breast cancer in the pilot study and are widely dispersed in the environment.
The organochlorine pesticides, like DDT, were widely used in the United States from the 1940s through the 1970s. Though still used in the third world, most have been banned in this country because of their high toxicity and evidence that they’re carcinogenic in animals. They tend to accumulate in the food chain and concentrate in animal fat and milk. Mary Wolff:
WOLFF: They’re stored in fat and stay around – some of them we think – for a person’s lifetime. PCBs and DDT, if they have a role in carcinogenesis, are thought to be promoters, that is, that they will take an initiating event and carry it along the road to cancer. That could happen in a number of ways.
SCHREIBER: Wolff says DDT and its metabolites are estrogenic, that is, they could act like estrogen it’s thought in promoting tumor growth. The organochlorines also affect an important system of enzymes in the body. The Israeli investigators think these changes could promote tumor growth itself, or deactivate the immune system, or destroy anti-cancer medications.
The fact that levels of pesticide residues found in human adipose tissues in the United States has been decreasing since the 1970s, while the breast cancer rate continues to rise, seems to contradict the Israeli observations. But New York University’s Paolo Toniolo points out that the chemicals could act differently at different exposure levels, and they’re unlikely to act alone.
TONIOLO: It’s probably complex interactions, if you allow me, between chemicals in the environment, endogenous hormones, dietary factors, that all concurrently act in a very complex way and ultimately will lead to a malignant transformation and a tumor.
SCHREIBER: Toniolo adds: That process could take 20 to 30 years, and age-at-exposure to chemicals in the environment is probably important. He also emphasizes that different individuals may be more or less predisposed to developing cancer. In the new study, Toniolo will add pesticide exposure to factors he’s examining in ongoing research involving 15,000 women attending a breast cancer screening clinic in New York.
Wolff and Toniolo’s new study will measure chemical residues in blood samples in a large population of women. And it takes into consideration reproductive factors, dietary habits, family history of cancer, and levels of hormones in the body. Results should be available in about a year.
CURWOOD: We’ve been listening to an excerpt of a piece by reporter Tatiana Schrieber back in September of 1991 on Living on Earth, and we decided to catch up now with Dr. Mary Wolff. She’s a professor of preventive medicine and ontological sciences at Mount Sinai School of Medicine. Dr. Wolff, welcome to Living on Earth.
WOLFF: Why thank you.
CURWOOD: So what happened? I mean, when we first interviewed you for that story back in 1991, you had just completed that pilot study on pesticide residues in breast fat and were about to start that larger study that looked at DDE and PCBs and possible links to breast cancer. What did you find?
WOLFF: Right, well that was a study with Dr. Toniolo and it was published in the Journal of the National Cancer Institute in 1993, and it made a huge splash. It was one of the most-cited papers of the 1990s and led to a bunch of copycat research investigations by me, among others, in different populations, and most of those were negative or had very small effects. And so over what’s been almost 20 years now, right, the consensus is that those chemicals probably have very little impact on breast cancer risk.
CURWOOD: So bottom line: DDT doesn’t cause breast cancer, at least as far as you and others have been able to tell.
WOLFF: Right, there are a couple of papers that suggest that if it had been measured early in life, we might be better able to establish risk. But using the current technology and currently-exposed populations, I don’t think that it’s considered a big problem for breast cancer.
CURWOOD: So you come out saying, ‘You know, folks, it’s probably unlikely then that DDT is directly linked to breast cancer.’ How do people receive this news?
WOLFF: Oh, well, there’ve been some very interesting responses. I mean, scientists take it as, you know, ‘well, that’s how it goes, on to the next project.’ But there’ve been some, sort of, faint damnation type papers, you know, undertaking foolish research, and, you know, following a wrong trail. But my feeling is that it was something that was worth pursuing, and that it has led to other studies on the effects of pesticides on reproduction and other intermediate endpoints that might be related to cancer or to other chronic disease, like cardiovascular disease and diabetes.
CURWOOD: So which pesticides, if any, do you think are linked to breast cancer?
WOLFF: Well, actually, now people look at this whole group of environmental chemicals that have hormonal activity, which again was cited as one of the mechanistic bases for those investigations. And what that work led us to was alluded to in your introduction: to look at intermediate risk factors, because if the window of exposure is long for cancer and detection, then maybe the effects of environment happen earlier in life.
So we got interested in events around puberty. You’ve talked about the risk in terms of breast cancer ¬– we got to be very interested in that, and particularly in minorities because at Mt. Sinai we serve a largely minority community. The black women in the United States get breast cancer, early onset breast cancer, at a higher rate than white women, and of course early onset breast cancer is the most aggressive, and at the same time, they also have earlier menarche than white women. So because environmental factors might be associated with all of those phenomena, we decided to look at exposures in the environment and their relationship to pubertal development in girls.
CURWOOD: Anything different you would do today with this research, knowing what you know?
WOLFF: Well one of the things that it’s led me and others to understand is how to use these biomarkers. So in that interview, Tatiana Schrieber was saying that what we thought was the best way to measure environmental exposures was to measure the actual levels in the body. One thing that that study and the many others that followed have taught us is that we don’t totally appreciate how long these chemicals stay in the body and what factors affect elimination and persistence.
So there’s a very interesting body of literature on that for DDT and related chemicals that I think may be valuable in using biomarkers. So I think maybe we were a little too simplistic, just because of lack of knowledge about how to use those measurements. And today, in fact, technology is driving a lot of measurements of environmental biomarkers, some of which are probably not based in good exposure science.
CURWOOD: So in other words, you’re saying chemical residues in a woman’s body doesn’t automatically predict disease. Well I want to thank you very much for helping us update our story from 20 years ago.
WOLFF: Thank you.
CURWOOD: Dr. Mary Wolff is a professor at Mount Sinai School of Medicine and directs the Center for Children’s Environmental Health and Disease Prevention Research.
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