The differential distribution of bacteria between cancerous and noncancerous ovarian tissues in situ Original paper

What was studied?

The differential distribution of bacteria between cancerous and noncancerous ovarian tissues in situ was examined to determine whether a distinct ovarian microbiome signature exists in ovarian cancer. This ovarian microbiome investigation used both immunohistochemistry for lipopolysaccharide (LPS) and 16S rRNA sequencing to verify bacterial presence and characterize microbial communities, offering evidence that ovaries—long assumed sterile—harbor resident bacteria.

Who was studied?

Sixteen women undergoing gynecologic surgery at a single center were included. The cancer group consisted of six women with serous ovarian carcinoma, while the control group comprised ten women with noncancerous ovarian conditions (uterine myoma or adenomyosis) whose ovaries were removed but were disease-free. Groups were matched for age, menopausal status, hypertension, diabetes, and parity, avoiding confounding factors affecting microbiome composition.

Most important findings

The study confirmed bacterial presence in both cancerous and noncancerous ovarian tissues through LPS immunostaining. 16S rRNA sequencing revealed that Proteobacteria, Firmicutes, and Bacteroidetes dominated both groups. However, important compositional shifts were detected. Cancerous ovaries showed significantly higher Aquificae and Planctomycetes and lower Crenarchaeota. At the species level, differences in Anoxynatronum sibiricum and Methanosarcina vacuolata were statistically significant, with Methanosarcina sharply reduced in cancer tissue. Predicted metagenomic functions (BugBase, PICRUSt) demonstrated enrichment of potentially pathogenic and oxidative stress–tolerant microbial phenotypes in cancerous ovaries. KEGG pathway analysis identified 46 differentially abundant pathways, with cancer tissues showing increased streptomycin biosynthesis, glycosphingolipid biosynthesis, glycerophospholipid metabolism, and methane metabolism, while pathways such as alpha-linolenic acid metabolism and fatty acid biosynthesis were reduced. These shifts suggest functionally distinct microbial ecosystems in ovarian cancer.

Key implications

These findings challenge the long-standing assumption of ovarian sterility and indicate that ovarian cancer is associated with altered bacterial composition and function. The enrichment of stress-tolerant and potentially pathogenic microbes suggests that bacteria may contribute to tumor microenvironment dynamics, possibly influencing inflammation, metabolism, and carcinogenesis. The distinct microbial signals—especially taxa like Methanosarcina vacuolata—offer promising avenues for microbial biomarkers of ovarian cancer. Understanding these microbial patterns may eventually support diagnostic, prognostic, and therapeutic strategies that integrate microbiome-based precision oncology.

Citation

Wang Q, Zhao L, Han L, et al. The differential distribution of bacteria between cancerous and noncancerous ovarian tissues in situ. Journal of Ovarian Research. 2020;13:8. doi:10.1186/s13048-019-0603-4