New research suggests that prostate cancer may be caused be a sexually-transmitted disease that a lot of people may not even know they have.  But some scientists say it’s probably too soon to add it to the list of cancers caused by infections and more research is needed.

The University of California scientists tested human prostate cells in the lab and published the results on the journal Proceedings of the National Academy of Sciences (PNAS).  They found that a sex infection called trichomoniasis aided cancer growth. 

The parasite that causes trichomoniasis is called Trichomonas vaginalis.  It produces a protein that causes inflammation and increased growth and invasion of benign and cancerous prostate cells.  An earlier study in 2009 found a quarter of men with prostate cancer showed signs of trichomoniasis, and these men were more likely to have advanced tumors.

Trichomoniasis is the most common non-viral sexually transmitted infection.  As many as 275 million people worldwide are infected.  But in many cases, a patient will have no symptoms (but when they do, the symptoms are icky) and be unaware that they have the infection.

Scientists are encouraged by the report, but cautious.

"(The) research was only done in the lab, and previous evidence in patients failed to show a clear link between prostate cancer and this common sexually transmitted infection,” said Nicola Smith, health information officer at Cancer Research UK.  “There’s been a lot of research into prostate cancer risk and we're working hard to piece together the puzzle.”

There’s evidence of genetic causes, as prostate cancer tends to happen in families.  And age is a factor.  The risk of being diagnosed with prostate cancer increases as a man gets older.  The risk of having prostate cancer by the age of 75 is 1-in-8 men.  But by the age of 85, the number increases to 1-in-6.