Bacterial infection linked to aggressive prostate cancer

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Men who are infected with the sexually transmitted bacterium Trichomonas vaginalis have a slightly increased risk of developing prostate cancer and double the normal risk of developing the aggressive form of the disease that spreads throughout the body, Harvard researchers reported today in the Journal of the National Cancer Institute.

It is the second report this week potentially linking infections to prostate cancer. On Monday, other researchers reported in the Proceedings of the National Academy of Sciences that they had found much higher levels of a mouse leukemia virus in prostate cancer tissue than in healthy tissues, and the presence of the virus was also associated with more aggressive tumors. Although neither the bacterium nor the virus has been definitively shown to be a causative agent in the tumors, the two reports suggest that inflammation caused by an infection could be a major factor in causing the tumors or in accelerating their growth.

T. vaginalisis the most common nonviral sexually transmitted infection, striking an estimated 174 million people worldwide each year. It is easily treated with antibiotics, but is symptomless in about three-quarters of men and goes untreated unless a female sexual partner is diagnosed with an infection.

Epidemiologist Jennifer Rider Stark of the Harvard School of Public Health and her colleagues studied 673 participants in the Physicians’ Health Study who had been diagnosed with prostate cancer and compared them with an equal number of healthy men in the study. Looking at blood samples collected 15 years earlier, they found that men who had antibodies to T. vaginalis in their blood were 23% more likely to develop prostate cancer and 2.17 times more likely to develop aggressive prostate cancer that spread to bones and elsewhere in the body, generally proving fatal.

Prostate cancer strikes more than 190,000 American men each year, killing more than 27,000. It is generally screened for with the prostate-specific antigen (PSA) test, but that assay identifies many tumors that progress only very slowly and for which no treatment is needed. Some studies have shown, in fact, that screening does not extend survival and leads to many unnecessary invasive procedures. Researchers have thus been searching for other markers that distinguish between prostate tumors that are aggressive and should be treated vigorously and those that grow very slowly and pose no threat to the bearer. The new findings provide a fresh lead in the search for such markers.

-- Thomas H. Maugh II