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Examining Perfluorinated Chemical (PFC) Exposure and its Relationship to Increased Risks of Endocrine Cancers, Ogbebor Enaholo Omoike, Epidemiology
Examining Perfluorinated Chemicals (PFCs)
Exposure and its Relationship to Increased Risks of Endocrine Cancers
Written by Hannah Warren
Prior to pursuing a Doctor of Public Health degree, Ogbebor had already completed his MD degree at the University of Benin in his home country of Nigeria, and his master’s in environmental health at the University of Michigan at Ann Arbor. Having already gained clinical experience while working as an MD, he came to the United States to gain the research experience needed to work in a teaching hospital in the Nigerian healthcare system. He was first drawn to research after working in hospitals and learning how point of care techniques are discovered through research. He had heard of current research that was coming out of ETSU’s College of Public Health, and was drawn to the program for its length, practical and leadership orientation, flexibility for research opportunities, and the strong Nigerian community.
Ogbebor Enaholo Omoike
Public Health, Dr.PH., concentration in Epidemiology
Dr. Liang Wang, Faculty Advisor
Having a background in clinical healthcare, environmental health, and epidemiology while working with some of the foremost scientists in these fields, Ogbebor wanted to incorporate these interests into his research for his dissertation. To accomplish this, he examined several individual chemicals in the perfluorinated chemical (PFC) family, which interfere with the endocrine system in a similar way to phthalates, another class of chemicals he studied while at the University of Michigan at Ann Arbor. These compounds are frequently used in the manufacturing process of everyday products including some non-stick cooking surfaces, furniture, clothing, and food packaging. These compounds are persistent in the environment, meaning they do not readily break down by photolysis or biodegradation, and can remain in the human body and environment for many years. An individual’s exposure to these compounds can be classified as either occupational, meaning they are exposed to these chemicals regularly through their work; or non-occupational, meaning they are exposed to the compounds at the level of an average American citizen through their routine activities.
Though the CDC, Agency for Toxic Substance and Disease Registry, Environmental Protection Agency and individual researchers have examined the effect of exposure to PFCs in animals, there has been little research examining the health risks associated with low level environmental exposures in humans. From the animal models, a variety of negative effects ranging from disruption of growth to reproductive and liver pathologies had been linked to PFCs. In his dissertation, Ogbebor examined five specific PFCs, which have been identified as endocrine disruptors that can interfere with the normal binding and functioning of hormones like estrogen. He hypothesized that chronic exposure to even low levels of these compounds like the dose someone with non-occupational exposure would experience, could increase an individual’s risk for certain endocrine cancers including breast, prostate, ovarian, and uterine cancers. Doctors are seeing increases in the number of endocrinelinked cancers from idiopathic (no known
Perfluorinated chemical compound
cause) origins. Each year, for the past close to twenty years, the United States government has evaluated levels of PFCs detectable in the blood of individuals who participated in national surveys. Ogbebor used this data for the foundation of his research.
To begin examining the large data set, Ogbebor created inclusion criteria that would limit data to only include results from individuals over the age of 20. From the data, he collected independent variables, which have been known to have and/or have shown associations with cancer in univariate analyses including (among others), age and gender, and the detectable quantity of each specified PFC in the individual’s blood serum, expressed in ng/ml. In the initial survey, each patient answered yes or no to either currently or previously having a diagnosis of an endocrine-linked cancer. From here, he established quartiles encompassing the range (in ng/ml) of levels of each PFC, which were detected in blood in a vast majority of the study participants. Once all samples had been assigned to a quartile, Ogbebor used a regression model with a binary logit function to predict health outcomes, specifically the presence or absence of cancer, with respect to exposure levels for each individual, when adjusted for covariates. He modeled the quartiles of exposure with respect to each other by comparing Q1 to Q2, Q3, and Q4. The more he worked with his model, the more he began to see associations with health outcomes.
His first major finding was that individuals who are exposed to the highest level of PFC’s in everyday life could have up to nine times higher odds of having an endocrine-linked cancer than individuals with the lowest levels of exposure.
While other researchers have previously described the increased risk of breast cancer associated with occupational exposure to PFCs, Ogbebor was able to use advanced statistical modelling to determine which PFC seemed to be most closely related to each type of endocrine cancer. These findings allowed him to postulate some thoughts on what cutoff limits for exposure might be proposed to help protect citizens. March and plans to publish three scientific papers to expand on his findings. He hopes to use his findings to propose threshold limits for exposure to legislators, and demonstrate that at and beyond the currently proposed limits, a significant increase in rates of particular cancers is likely to be seen; and hopefully, this would influence policy. Because it is already known that these chemicals stay in the body many years after exposure, it is particularly important to help policy makers understand the biological and economic impact they can have on society. As a clinician he frequently saw cancers of unknown origin, and he hopes that this and future research can help to explain the origin of these cancers.
Throughout his education at ETSU, Ogbebor has worked with Dr. Liang Wang, Associate Professor of Epidemiology, as his mentor. Dr. Wang always encourages students to find the area they are passionate about and encourages them to become an expert in that area. As an international student, Ogbebor has faced challenges that not every student or professor can relate to, but he is grateful to have had the opportunity to work with Dr. Wang and other professors that understand the unique challenges that arise from studying in a foreign country. According to Ogbebor, “Every student and their situation is unique. Find what your heart is passionate about and pursue it. When you follow your heart, you will find extra strength when the road gets tough. Take time to find a mentor that understands and challenges you. Do not be afraid to seek advice and ask questions”. His favorite part of his dissertation has been fulfilling his dream of uncovering associations that were previously unknown. In addition to Dr. Wang, his appreciation goes to other dissertation committee members, including Drs. Robert Pack (Professor and Associate Dean), Hadii Mamudu (Associate Professor), and Ying Liu (Assistant Professor). After graduation he plans to apply to a post-doctoral fellowship, and to one day return home to Nigeria to continue to seek the undiscovered and work in a health system to practice public health, and also be actively engaged in clinical research and practice.
Left, Dr. Liang Wang, Right, Ogbebor Enaholo Omoike
