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.

Ovarian Cancer Statistics. Centers for Disease Control and Prevention. June 6, 2022.

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.

What Are the Symptoms of Ovarian Cancer? Centers for Disease Control and Prevention. August 31, 2022.

 

 

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.

Sipos A, Ujlaki G, Mikó E, et al. The role of the microbiome in ovarian cancer: mechanistic insights into oncobiosis and to bacterial metabolite signaling. Mol Med. 2021;27(1):33.

 

 

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

Reid BM, Permuth JB, Sellers TA. Epidemiology of ovarian cancer: a review. Cancer Biol Med. 2017;14(1):9-32.

 

 

What is oncobiosis?

 

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.

Wang Q, Zhao L, Han L, et al. The differential distribution of bacteria between cancerous and noncancerous ovarian tissues in situ. J Ovarian Res. 2020;13(1):8.

Poore GD, Kopylova E, Zhu Q, et al. Microbiome analyses of blood and tissues suggest cancer diagnostic approach. Nature. 2020;579(7800):567-574.

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.

Asangba AE, Chen J, Goergen KM, et al. Diagnostic and prognostic potential of the microbiome in ovarian cancer treatment response. Sci Rep. 2023;13(1):730.

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. 

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. 

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.