Ovarian cancer’s link to the microbiome

By Alpana Mohta, MD, DNB, FEADV, FIADVL, IFAAD | Medically reviewed by Jeffrey A. Bubis, DO, FACOI, FACP
Published May 11, 2023

Key Takeaways

  • Neoplastic diseases often involve alterations to the microbiome, a phenomenon known as oncobiosis, which contributes to their development. 

  • Researchers for the Mayo Clinic identified the enrichment of certain microbial taxa, including Dialister and Corynebacterium, in the microbiome of ovarian cancer patients—which could serve as potential indicators for early detection.

  • The researchers also found that specific bacteria present in the reproductive tract and stool of ovarian cancer patients may be linked to adverse outcomes and drug resistance, indicating their potential use in predicting treatment response.

Ovarian cancer is the second most prevalent gynecologic cancer in the United States. It's also the deadliest, taking more lives than any other female reproductive system cancer.[] This sobering fact underscores the urgent need for increased awareness, research, and action to combat this devastating disease.

Clinical picture of diagnosis

During the early stages of ovarian cancer, symptoms may be absent or minimal. However, when symptoms occur, they may initially include pelvic discomfort or pressure, unexpected vaginal bleeding, abdominal or back pain, bloating, and changes in bowel or urination patterns.[]

Some women have a higher risk of ovarian cancer

While genetics play a role in about 20% of ovarian cancer cases, the cause of the remaining 80% can be acquired, according to a review published in Molecular Medicine.[] 

Women who have had fewer pregnancies, have never been pregnant, started menstruating at an early age (before 12), and/or experienced menopause after the age of 50 are at a higher risk of ovarian cancer. 

However, periodic suppression of ovulation by oral contraceptives, pregnancy, or lactation reduces the risk.[]

What is oncobiosis?

Neoplastic diseases often involve alterations to the microbiome, a phenomenon known as oncobiosis, which contributes to their development. 

This stands in contrast to eubiosis, where a healthy microbiome is present. 

Microbiome-neoplastic cell interactions impact multiple cancer-related events, as noted in the Molecular Medicine review, such as: 

  • Changes in the microbiome can alter gene expression, cellular functions, and key events related to cancer growth and spread.

  • In some cases, these changes can lead to inflammation and increase the risk of cancer.

  • Bacterial metabolites can either promote or hinder tumor growth, depending on their effects on oxidative stress.

  • Certain metabolites can also alter how the immune system responds to cancer cells.

Several studies have found significant levels of Proteobacteria and Fusobacteria/Bacteroides in the tumor tissue of ovarian cancer patients.[][] Genital pathogens like human papilloma virus (HPV) 16, HPV 18, Chlamydia trachomatis and Nesseria gonorrhoeae increase the risk for ovarian cancer.

But there is still a dearth of evidence for the microbiomes' potential role in the disease's early detection, diagnosis, and prognosis. A recent study from Mayo Clinic's Center for Individualized Medicine discovered colonization of specific microbes in the reproductive tract of ovarian cancer patients.[] As recorded in Scientific Reports, the study compared samples from 30 women who underwent hysterectomy for ovarian cancer and 34 women who underwent hysterectomy for a benign condition. The samples were obtained from various areas of the reproductive tract and analyzed using high-throughput sequencing. 

Role in diagnosis 

The Mayo Clinic researchers uncovered a distinctive trend indicating that women with early-stage ovarian cancer experience a more significant buildup of pathogenic microbes than those with advanced-stage disease. 

As the disease progresses, the quantity of microbes decreases.

A unique microbial community was found in the ovarian cancer group, characterized by an overall increase in various microbial taxa, such as Corynebacterium, Dialister, Prevotella, and Peptoniphilus, across all body sites.

Lactobacillus species were downregulated in the lower reproductive tract (LRT) of ovarian cancer patients, according to the report. The researchers also discovered a higher relative abundance of Bacteroides in these cancer patients' uterus, fallopian tubes, ovaries, and ascites. The study also discovered a statistically significant enrichment of numerous harmful bacteria, including C. tuberculostearicum and F. hominis, both of which are recognized pathogens, in the LRT of the ovarian cancer cohort. 

These findings show that the overwhelming abundance of recognized pathogens in the ovarian cancer cohort's lower reproductive tract could play a crucial role in the early diagnosis of ovarian cancer.

The study also made some groundbreaking discoveries on specific microbial fingerprints that could be used to predict the stage, grade, histology, and prognosis of ovarian cancers.

Role in therapeutics

Microbes have been linked to the efficacy of cancer therapies in several studies. The Mayo Clinic researchers identified the presence of Bacteroides ovatus, V. parvula, and A. christensenii in ovarian cancer patients' reproductive tract and stool to be linked with adverse outcomes, and Dialister species such as D. invisus, D. micraerophilus, and D. propionicifaciens to be associated with possible multi-drug resistance. Additional research is needed, but these findings suggest that these microbes may influence tumor response to ovarian cancer therapy.

What this means for you

This distinct pattern of microbiome is a noteworthy discovery and could be pivotal in the early detection of ovarian cancer, potentially saving lives. As with the noninvasive Pap smear for cervical cancer detection, the microbiome signatures may enable healthcare professionals to identify and diagnose the disease in its early stages, resulting in better patient outcomes.

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