A fact often lost in the charity walks and commercials that have dramatically raised awareness of breast cancer over the past two decades is that beneath the diagnostic umbrella of “breast cancer” are numerous types of tumors. Other than the fact that all of these tumors are found in breast tissue, different forms of breast cancer grow at different rates, will express different types of hormone receptors or genes that can act as drug targets, and are more or less likely to become “invasive,” spreading throughout the body. To complicate matters further, not every population experiences these different types of breast cancer in equal proportions – black women in the United States have a poorer survival rate for breast cancer than white women, and women in Africa have an equal breast cancer mortality rate to North American women despite four times as many diagnoses of the disease in the U.S., Canada and Mexico.
University of Chicago Medical Center researcher Olufunmilayo Olopade (Funmi, for short) has dedicated her career to the study of these discrepancies since moving to Chicago from her home country of Nigeria in the 1980’s. Olopade, a professor of medicine and human genetics, has received several accolades for her work, including the prestigious MacArthur fellowship (known sometimes as the “genius grant”) in 2005. On Tuesday evening, she’ll give a lecture at the Harold Washington Library Center in Chicago titled “Nature, Nurture and Breast Cancer” that will explain what we know about the genetic and environmental factors that cause the disease in more than 200,000 American women each year.
In a recent Journal of Clinical Oncology paper, Olopade and colleagues from Chicago, Senegal and Nigeria looked for physiological reasons to explain the differences in breast cancer rates and outcomes between American and African populations. Learning more about these differences could help direct women into the most effective treatments for their particular type of breast cancer, Olopade said, as well as offer clues as to how genes versus the environment cause breast tumors to arise.
“Breast cancer doesn’t affect all individuals the same way,” Olopade said this past weekend, as she prepared for Tuesday’s lecture. “What we found is that the types of cancer that people get in different populations differ, that’s why when we talk about personalized medicine at an individual level we also have to talk about it on a population level.”
In a pool of over 500 breast cancer patients from Senegal and Nigeria, researchers found a dramatically increased rate of more dangerous tumor types that are unresponsive to some commonly used treatments. Tumors that contain estrogen receptors typically grow more slowly and are often treatable with the drug tamoxifen, which blocks those receptors and slows the tumor’s growth. But while ER-positive tumors are observed in more than 60% of African-American women, only a quarter of the African women in Olopade’s sample group exhibited tumors with estrogen receptors. Compared to Asian, white and African-American populations, the African women also had about half the occurrence of luminal cancers – tumors that are slow-growing and tamoxifen-sensitive – and double the occurrence of basal cancers, which lack estrogen and progesterone receptors and grow rapidly.
The vastly different proportion of tumors seen in African women and other races suggest genetics play a role in the types of breast cancer expressed in each population. But because most African-Americans connect back to West African origins, the genetics between those two populations are presumably similar. So the differences in tumor type between African and African-American women suggest that environmental factors – diet, hormone therapies, physical activity – contribute as well.
“The commonality between African women and African-American women is their common genetic ancestry, but they live in vastly different environments, so we have to now think about what is the role of gene-environment interaction,” Olopade said.
In the meantime, Olopade also continues to work with colleagues to improved diagnosis of breast cancer tumors, which are more easily treatable if detected early. Another recent paper, published by Olopade with Milica Medved, Gregory Karczmar and other members of the University of Chicago Department of Radiology, explored a new method of using MRI machines, rather than mammograms, to detect tumors (an oft-discussed issue). Genetic techniques may also advise women about their relative risk for cancers that arise earlier in life and grow more rapidly, directing high-risk patients towards earlier and more frequent screening. In her talk Tuesday, Olopade said she will talk about how the latest scientific discoveries have advanced these causes, while identifying mysteries of breast cancer that still need to be explored.
“I think breast cancer is not as dangerous as it used to be,” Olopade said. “However – yes, we can treat it and yes, we have drugs for it, but the research still can’t be completed. We still need to look for targets so that all women who have breast cancer can be assured they have a treatable disease.”
(For coverage of Dr. Olopade’s lecture at the Washington Library, check back to the blog later this week. Or better yet, go to her talk! It’s free!)