The microbiome of the human body is currently one of the most popular areas of research. A significant portion of this research has focused on the gut microbiome and its role in various conditions including inflammatory bowel disease, irritable bowel syndrome, and colorectal cancer. As this type of emerging research continues to develop, the microbiome within other organ systems will undoubtedly begin to draw the same level of attention. One such area is the microbiome of prostatic fluid, namely in patients with elevated levels of prostate specific antigen (PSA) and prostate cancer (PrCa).
This type of research is still developing, but it has been postulated that an inflammatory environment within the prostate, which can be seen in chronic prostatitis and PrCa, could be secondary to or a potential primary cause of bacterial population modifications.1,2 The bacteria that have been previously implicated in prostate inflammation include Escherichia coli, Neisseria gonorrhoeae, Chlamydia trachomatis, Pseudomonas, Trichomonas vaginalis, and Propionibacterium acnes.1-3
Recently a research group led by Ma and colleagues from China published a study evaluating the microbiome of prostatic fluid in patients with elevated PSA.3 The authors evaluated the microbiome of prostatic fluid in 59 patients undergoing prostate biopsy for elevated PSA (> 4 ng/mL). The prostate fluid was collected directly before the patient underwent prostate biopsy. The prostatic fluid was then analyzed using 16S rRNA gene sequencing.
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No patients had a history of a recent sexually transmitted disease, prostatitis, urinary tract infection, or antibiotic exposure for at least 4 weeks. After evaluating the prostate biopsies, 32 patients were found to have PrCA, with 27 patients in the non-PrCa group.
Based on results of the sequencing, patients diagnosed with PrCa were found to be more likely to have a lower microbial diversity compared with those without cancer. There were no unique bacterial species found in either group; therefore, some bacteria were associated with both cancer and noncancer diagnoses.
The bacteria found in both groups included Streptococcus, Carnobacterium, Oceanobacillus, Paenibacillus, Alkaliphilus, Cronobacter, Lactococcus, Enterococcus, and Bacillus amongst others. The following bacteria were found to be statistically significantly more commonly seen in the PrCa group: Enterobacter, Lactococcus, Carnobacterium, Streptococcus, and Geobacillus. On the contrary, the following bacteria were statistically significantly seen more in the noncancer group: Alkaliphilus, Cronobacter, and Paenibacillus.
Based on these data, the researchers developed a receiving operational curve (ROC) which found that by using the preceding 8 bacteria with statistically significant differences between groups, a microbiome analysis could potentially be used as a diagnostic test for PrCa. The area under the curve (AUC) was calculated at 0.72, which the authors suggested was an indication that it could have the microbiome could have a role in the diagnosis of PrCa.
There were several limitations to this study including the limited number of patients. The specific diagnoses of the patients who did not have cancer on biopsy were not included and would have been interesting to evaluate with respect to the microbiome. In addition, all of the patients were from a single center in China, therefore, the results may not be directly relatable to the patient population typically seen in the United States. It would have also been interesting to see if there were any further differences in the microbiome composition based on patient staging, response to therapy, or overall outcomes.
This study raises several interesting points. If there truly are differences in the microbiome composure in patients with PrCa, future research could seek to alter the microbiome, either with dietary changes, antibiotics, probiotics/prebiotics, or even fecal transplantation to see if these changes could alter disease course. These types of studies would have to ensure long term follow-up in order to accurately track patients after an intervention. Additional research could also determine if there are certain bacterial species that could help aid in the diagnosis of PrCa, especially considering some of the recent controversies involving PSA.
References
- Cohen RJ, Shannon BA, McNeal JE, Shannon T, Garrett KL. Propionibacterium acnes associated with inflammation in radical prostatectomy specimens: a possible link to cancer evolution? J Urol. 2005;173(6):1969-1974.
- Cavarretta I, Ferrarese R, Cazzaniga W, et al. The microbiome of the prostate tumour microenvironment. Eur Urol. 2017;72(4):625-631.
- Ma X, Chi C, Fan L, et al. The microbiome of prostate fluid is associated with prostate cancer. Front Microbiol. 2019;10:1664.
