Mammographic density – how dense breast tissue is – is a strong risk factor for breast cancer. Women with the highest mammographic density are at a four- to six-fold greater risk of breast cancer than women with the lowest density. Women with dense breasts have more glandular and fibrous tissue and less fatty tissue in the breast – but no one knows why. Rulla M. Tamimi, ScD, wants to solve this mystery so that she can ultimately improve outcomes for breast cancer patients. Tamimi, who works in the Channing Division of Network Medicine, is using the tools of molecular epidemiology to investigate.
Inside a Molecular Epidemiologist’s Toolbox
As a molecular epidemiologist, Tamimi seeks to understand the contribution of genetic and environmental risk factors of breast cancer at the molecular scale. She and her team take advantage of genome-wide association studies to identify genetic risk markers, blood and tissue samples to identify circulating markers or hormones, and they employ machine learning techniques to identify features of a mammogram.
By leveraging molecular tools, Tamimi hopes to shed new light on the distribution and risk factors of breast cancer. “I think of epidemiology as a toolbox. We can use it to answer questions about diseases, and the tools can be as complex or simple as the question you are asking,” said Tamimi. “What I do is ask questions mostly about breast cancer and how certain risk factors, specifically high mammographic density, may be related to breast cancer.”
Tamimi seeks to discover not only how mammographic density and breast cancer are connected but also why. “My work is split between trying to understand the modifiable risk factors for breast cancer and identifying the molecular underpinnings of how breast cancer develops,” explained Tamimi. “We need to be able to understand the underlying mechanisms to help us identify the places where we can intervene and help patients.”
A Unique Research Opportunity
To begin to uncover the relationship between mammographic density and breast cancer risk, Tamimi’s current work is focused on identifying early-life risk factors that lead some women to develop dense breasts and some women to develop fatty breasts. Tamimi and her colleagues have had an opportunity to screen a large cohort of women and get information about their risk exposures over a lifetime through the Growing Up Today Study, or GUTS. GUTS participants are a unique cohort of over 27,000 young adults, for whom there is 20 years of data collected during adolescence and young adulthood in addition to nearly 30 years of data from their mothers, who continue to participate in the Nurses’ Health Study II.
As the study director of GUTS, Tamimi hopes to follow up with more than 14,000 women to collect information on their early-life diet, birth characteristics, breastfeeding history and incidence of benign breast disease. Tamimi hopes to recruit GUTS women who live close to BWH to have their mammographic density measured noninvasively. This comprehensive approach will allow Tamimi and her colleagues to understand the mechanisms by which early-life risk factors are associated with high mammographic density and, consequently, increased breast cancer risk.
But Tamimi doesn’t want to stop there. “GUTS is an excellent opportunity for researchers across BWH to ask a variety of research questions, not just about breast cancer,” said Tamimi. “The beauty of this cohort is that they cover such a wide array of exposures and outcomes. I encourage anybody who is interested in leveraging this resource to reach out about a collaboration. Collaborations are what make the Brigham special. Being able to do interdisciplinary research in a team makes the research so much stronger – and it makes the experience much more rewarding.”