Propionibacterium acnes, anaerobic gram-positive bacilli responsible for inflammatory acne.
When someone mentions cancer in men, most will immediately think of the prostate. This gland is primarily responsible for male urogenital health. It also may be vulnerable to the onset of tumours, both benign and malignant. As a result, some 24,000 Canadian men are afflicted each year and sadly some 4,000 will die.
The cause of prostate cancer has been intensely studied for decades. Researchers have found about five to ten per cent of cases are due to inherited genes. However, the vast majority of cases occur spontaneously over the course of a lifetime. Risk factors such as age and dietary choices have been identified, and tests do exist to identify biological warning signs. Yet, there is still one particular piece of the puzzle missing. Something has to trigger the process.
What causes this spontaneous change has been the focus of many studies, and several biological molecules have been identified as playing a role. The most common are testosterone and prostate-specific antigen (PSA), although in recent years others have surfaced, including prostate cancer antigen 3 (PCA3) and insulin growth factor 1 (IGF-1). While higher levels may indicate a higher risk for disease, they do not, however, indicate a possible trigger.
One route to identify the trigger involves understanding the body's response to an infection. When an unwelcome bacterium or virus enters a restricted area such as the prostate, the cells may respond by trying to kill the intruder. To accomplish this, they rely on inflammation as well as the generation of a number of toxic molecules known as reactive oxygen species. These are quite effective at harming the microbes, yet there is a cost to the cell itself: if these chemicals are continually produced, they may end up interfering with the genetic copying process. If mutations occur in those oncogenes, the result could be the initiation of a tumour.
The concept appears to be valid as bacteria have been found in the prostate, particularly in men suffering from prostate-related pain. Many of the species happen to come from the skin, although for the most part they are not considered to be pathogenic as they are normal members of the skin microbial population.
But in 2005, the discovery of one particular bacterial species in the prostate sounded the alarm that infection may indeed be the cause. It was Propionibacterium acnes. For researchers trying to find the prostate cancer trigger, this bacterium became a potential suspect.
There was little doubt of a strong association between the species and cancer.
The reason comes from the troubles P. acnes causes. As the name implies, the bacterium is involved in the formation of acne on the skin. As anyone who has suffered from this ailment knows, inflammation is a constant problem and leads to damage to the skin and underlying tissue.
Though the theory was valid, it wasn't entirely accepted even as P. acnes was found to live in prostate cancers. Yet, researchers continued to find some route to show at least an association between the bacterium and the disease. Last week, even more evidence linking the bacterium and prostate cancer was shown by a Swedish team of researchers. They revealed the results of a six-year study trying to determine if this acne-causer was also involved in the onset of cancer. Based on their results, the presence of this bacterium may offer at the least another risk factor, if not a possible trigger.
The team examined prostate tissue sections collected from 2009 to 2015. They were able to acquire biopsies from both men suffering from cancer and healthy controls. The samples were incubated for seven days to give the bacteria time to adapt to the new environment and then grow. After the week was over, the team looked for colonies and then used genetic techniques to identify any that showed up.
When the results came back, the bacterium was found in 60 per cent of the prostate cancer cases, as opposed to 26 per cent of the controls. Although the team had hoped to see 100 per cent presence in tumours and zero in the controls, the results were still significant. There was little doubt of a strong association between the species and cancer.
While this study does imply a role of P. acnes in the development of prostate cancer, this was not a smoking gun. As a result, the authors had to admit the study only added more evidence in the case against the bacterium. They did show, however, the bacterial isolate had the capability of causing inflammation and as such could indeed initiate the formation of tumours.
Although this study didn't offer a conclusive role for P. acnes, the results do suggest the presence of this bacterium in biopsy samples may be another risk factor to consider. If combined as a screen in combination with other easier-to-collect biomarkers, there may be a possible route for prevention through treating the bacterial infection before it has the chance to at least contribute -- if not actually cause -- cancer.
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