The human body’s microbial community is thought to have such intricate and profound effects on human health that it is often referred to as the hidden organ. By evolving together over thousands of years, indwelling microbes and their human hosts have developed a mutually beneficial relationship. The relationship is so intertwined that one can think of the human body as one superorganism made of both human and microbial cells.60
From birth through the early years of life, countless different bacteria colonize the body. These trillions of microbes form the human microbiome, which is influenced by genetic, environmental, and lifestyle factors (such as diet, medication use, and physical activity). Because of this, the composition of the microbiome varies from one person to the next.60
Recent research has shown that the microbiome plays an important role in maintaining and influencing key physiologic activities, including normal metabolism and immune function. Laboratory and clinical evidence suggest that changes in specific organisms in the microbiome may lead to the development of disease, including cancer.
When it comes to cancer, the body’s microbes can be both harmful and beneficial. Although certain microbes may promote cancer growth, others seem to bolster the body’s immune defenses against cancer or help cancer treatments work better.60
Microbiome research is a young and fast-growing field; however, it is not yet clear that specific microbes have beneficial or detrimental roles in cancer development. As such, research efforts are expanding.
The Microbiome Shapes Cancer Risk
While much work has focused on the gut microbiome, researchers have found that changes in oral and vaginal microbiomes could be associated with modified disease risk as well. Many investigations have found links between the abundance of specific organisms that comprise the microbiome and the risk of colon, squamous cell, and esophageal cancers. These observations suggest that modulating the microbiome in individuals at high risk of developing certain malignancies may be a cancer prevention strategy worth exploring.
Over the past several years, two federally funded studies looked at oral mouthwash samples from people to determine the presence of specific bacterial microbes. One study enrolled 383 patients and controls to examine how the microbiome might influence head and neck squamous cell cancer.61 Researchers noted that people who developed this disease were more often current tobacco smokers, consumed moderate to high levels of alcohol, and were human papillomavirus type 16 positive (this study was funded, in part, by NCI).
For patients with head and neck squamous cell cancer, researchers found that while the overall composition of the microbiome was not associated with increased cancer risk, an abundant amount of Corynebacterium and Kingella bacteria was associated with a decreased risk.
Another study looked at the prevalence of oral bacteria in 106 patients with esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC)62 (this study was funded, in part, by NCI). The periodontal pathogen Tannerella forsythia was associated with higher risk of EAC, whereas depletion of Neisseria and Streptococcus pneumoniae bacteria was associated with lower EAC risk. For ESCC, the abundance of the periodontal bacterium Porphyromonas gingivalis conveyed higher risk of the cancer.
It is too soon to offer a strategy for using the microbiome to modify cancer risk or progression; however, the findings of these two studies could inform the basis for future research on effective approaches for prevention or treatment of some head and neck cancers.
Though there are still many questions to answer about the microbiome, it is known that a lifestyle involving a well-balanced diet and exercise can promote a diverse microbiome associated with good health. In the future, cancer care may even include an analysis of the patient’s microbiome at diagnosis to inform personalized treatment planning. ASCO will continue to monitor progress in this complex but fascinating field of research and will report on progress in understanding the microbiome and cancer in future editions of Clinical Cancer Advances.
Voices for Cancer Research: Judith Kaur, MD
“In medical school the doctors I worked with were so hopeful that we would find something better to offer our patients, and indeed, every year, thanks to cancer research, there has been something new.”
Dr. Kaur grew up in the inner city of Chicago and was the first in her family to graduate from high school and college. As a young female student with a passion for science and an admiration for teachers, in the 1960s Dr. Kaur was encouraged to pursue one of the few professions thought to be suitable for women at that time – science teacher. It wasn’t until her husband challenged her to go to medical school that she seriously considered it. Dr. Kaur was later accepted to the Indians into Medicine Program at the University of North Dakota, a federal program that recruits Native Americans, like Dr. Kaur, into medical school.
Later on, Dr. Kaur received the very first Young Investigator Award from the Conquer Cancer Foundation of ASCO, which provides grant funding to early-career researchers to begin and establish the direction of their cancer research. She received the award for her innovative work in creating monoclonal antibodies for use in melanoma, a treatment unheard of at the time but now a standard of care.
Dr. Kaur has become a pioneer in women’s cancer research and education, particularly in breast and cervical cancers. She incorporates her love for teaching into her clinical practice every day and stresses the importance of personalized education to overcome cancer health disparities across the country. “It comes down to having the best treatment for the right patient for the right reason, every time you see them,” said Dr. Kaur.
Today, Dr. Kaur leads the Spirit of Eagles, a program that focuses on including Native Americans in research training and education and provides culturally tailored materials for tribes across the country. Through her leadership and research, Dr. Kaur’s efforts are increasing clinical trial participation, improving cancer prevention, and supporting students interested in pursuing careers in medicine.
Dr. Kaur is an oncologist and medical director for the Native American Programs in the Mayo Clinic Cancer Center in Jacksonville, Florida. Disclosures include honoraria and travel, accommodations, and expenses from Lilly.
To learn more about why Dr. Kaur lives to conquer cancer, please visit asco.org/live-to-conquer-cancer.