Cervical cancer may be driven by imbalance in vaginal bacteria, research finds

June 4, 2018, University of Arizona
Cervical cancer may be driven by imbalance in vaginal bacteria, UA research finds
Endometrial cells colonized with 'good' bacteria called Lactobacillus crispatus (colored purple). Credit: Herbst-Kralovetz lab

Virtually all cervical cancers are caused by HPV, or human papillomavirus, dubbed the "common cold" of sexually transmitted infections because nearly every sexually active person catches it. Fortunately, the immune system vanquishes the majority of HPV infections, with only a small percentage progressing to precancer and, ultimately, cancer. But why do some people clear the infection while others are unable to fight it?

To answer that question, a team led by the University of Arizona Cancer Center's Melissa M. Herbst-Kralovetz, Ph.D., associate professor at the UA College of Medicine—Phoenix, studied 100 premenopausal women to find links between vaginal and .

Her team found that women without cervical abnormalities are hosts to different communities of vaginal bacteria than women with cervical cancer and precancer, a discrepancy that reveals a direct relationship between "good" bacteria and cervical health, and "bad" bacteria and increased cancer risk. The results were published online May 15 in the open-access Nature publication Scientific Reports.

The microbiome is the community of microbes that take up residence in the body. Some species of bacteria—such as lactobacilli, which are related to but distinct from the probiotics found in yogurt—have been found to promote a healthy vaginal environment. For example, previous research revealed women with Lactobacillus gasseri-dominant vaginal microbiomes are more likely to clear HPV infections. Good bacteria also can hold territory to keep bad bacteria from moving in. Sometimes, however, they lose this turf war.

"In cancer and precancer patients, lactobacilli——are replaced by a mixture of bad bacteria," said Dr. Herbst-Kralovetz. In the study, as Lactobacillus populations dwindled, cervical abnormalities became more severe. On the other hand, bad bacteria, called Sneathia, were linked to HPV infection, precancer and cervical cancer.

Sneathia are rod-shaped bacteria that can grow into fibrous chains. They have been associated with other gynecological conditions, including bacterial vaginosis, miscarriage, preterm labor, HPV infection and cervical precancer. Dr. Herbst-Kralovetz's study is the first to find that a substantial Sneathia population is associated with all stages of the HPV-to-cancer continuum, from initial HPV infection to precancer to .

What's unknown is whether Sneathia species actively promote HPV infection or cancer formation, or if they're just along for the ride. The current study offers only a snapshot of women at one point in time. To establish a cause-and-effect relationship, future studies must follow women over time.

"There's really not a lot in the literature about how Sneathia functions in the reproductive tract," said Dr. Herbst-Kralovetz. "How Sneathia may be impacting the hallmarks of cancer is an active area of investigation in our lab."

The bacteria that make up the vaginal microbiome are inextricably linked to the acidity of the vaginal environment. A vagina with a pH of 4.5 or below defends against harmful bacteria that are unable to survive in such an acidic environment. When pH is elevated, harmful bacteria gain the opportunity to move in, disrupting the vaginal ecosystem.

"High pH is a great reflection of the vaginal microbiome composition," said Dr. Herbst-Kralovetz. "Lactobacilli produce lactic acid that directly lowers the pH. If you have high levels of lactobacilli you're going to have a lower vaginal pH, and that's associated with health."

Dr. Herbst-Kralovetz's team found that, as the vaginal environment loses acidity, cervical abnormalities become more severe. The team is the first to show a relationship between elevated pH and advanced cervical abnormalities.

Roughly half of the patients studied were Hispanic, while the other half were of non-Hispanic origin. Hispanic women have the highest incidence of cervical cancer of all racial and ethnic groups, according to the National Cancer Institute. Studies assessing factors such as race and ethnicity in cancer risk are important for understanding why some populations are disproportionately affected by cancer.

"I wanted to truly reflect the Arizona population in our study," said Dr. Herbst-Kralovetz. "Latinas are at a higher risk of cervical cancer. A long-term goal of mine is to help address that health disparity."

The team found that Hispanic women were more likely to have decreased Lactobacillus populations and increased Sneathia populations. Perhaps differences in the is one factor behind Hispanic women's increased risk for cervical .

"One of our duties at the UA Cancer Center is to improve the health of Arizonans," said William Cance, MD, deputy director of the UA Cancer Center at Dignity Health St. Joseph's Hospital and Medical Center. Referring to the UA's recent designation as a Hispanic Serving Institution by the U.S. Department of Education, Dr. Cance added, "Studies such as those being led by Dr. Herbst-Kralovetz show our commitment to supporting not just the education of Hispanics in Arizona, but also their health."

"This was a highly collaborative group, performing a multi-site study here in the Phoenix area," concluded Dr. Herbst-Kralovetz. "This work serves as the foundation for a lot of other studies. It creates many hypotheses and future directions for us in the lab, and also allows us to address some of these health disparities here in Arizona."

Explore further: Does HPV vaccination prevent the development of cervical cancer?

More information: Paweł Łaniewski et al. Linking cervicovaginal immune signatures, HPV and microbiota composition in cervical carcinogenesis in non-Hispanic and Hispanic women, Scientific Reports (2018). DOI: 10.1038/s41598-018-25879-7

Related Stories

Does HPV vaccination prevent the development of cervical cancer?

May 8, 2018
New evidence published today in the Cochrane Library shows that human papilloma virus (HPV) vaccines protect against cervical lesions in young women, particularly in those who are vaccinated between the ages of 15 and 26. ...

Study finds concerning connection between feminine hygiene products and infection

April 16, 2018
Vaginal hygiene products have been used by 95 per cent of Canadian women, but they likely do more harm than good, according to a University of Guelph study.

Screening, HPV vaccine can prevent cervical cancer: FDA

February 8, 2017
(HealthDay)—Women can reduce their risk of cervical cancer through vaccination and screening, the U.S. Food and Drug Administration says.

5 things you should know about cervical cancer

December 1, 2017
(HealthDay)—A little knowledge can go a long way in the fight against cervical cancer.

Facts women and men should know about cervical cancer

January 22, 2018
January is Cervical Cancer Awareness month and the message from the Centers from Disease Control and Prevention is that "no woman should die from cervical cancer."

Cervical cancer frequently diagnosed after age 65

March 28, 2018
(HealthDay)—A considerable proportion of women are diagnosed with cervical cancer after age 65, according to a study presented at the Society of Gynecologic Oncology's Annual Meeting on Women's Cancer, held from March 24 ...

Recommended for you

Research team discovers drug compound that stops cancer cells from spreading

June 22, 2018
Fighting cancer means killing cancer cells. However, oncologists know that it's also important to halt the movement of cancer cells before they spread throughout the body. New research, published today in the journal Nature ...

Dying cancer cells make remaining glioblastoma cells more aggressive and therapy-resistant

June 21, 2018
A surprising form of cell-to-cell communication in glioblastoma promotes global changes in recipient cells, including aggressiveness, motility, and resistance to radiation or chemotherapy.

Existing treatment could be used for common 'untreatable' form of lung cancer

June 21, 2018
A cancer treatment already approved for use in certain types of cancer has been found to block cell growth in a common form of lung cancer for which there is currently no specific treatment available.

Novel therapy makes oxidative stress deadly to cancer

June 21, 2018
Oxidative stress can help tumors thrive, but one way novel cancer treatments work is by pushing levels to the point where it instead helps them die, scientists report.

Higher body fat linked to lower breast cancer risk in younger women

June 21, 2018
While obesity has been shown to increase breast cancer risk in postmenopausal women, a large-scale study co-led by a University of North Carolina Lineberger Comprehensive Cancer Center researcher found the opposite is true ...

Researchers uncover new target to stop cancer growth

June 21, 2018
Researchers at the University of Wisconsin-Madison have discovered that a protein called Munc13-4 helps cancer cells secrete large numbers of exosomes—tiny, membrane-bound packages containing proteins and RNAs that stimulate ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.