Prostate cancer linked to common STI

“Prostate cancer could be a sexually transmitted disease caused by a common infection,” The Independent reports.

Researchers have found evidence of a link between the cancer and trichomoniasis – a common parasite that is passed on during unprotected sexual contact.

A laboratory study found the parasite produces a protein similar to a human protein that is necessary for the immune system to function. However, the human protein had also been shown to be involved in the growth of cancers, as it causes inflammation.

This is of potential concern as trichomoniasis causes no noticeable symptoms in up to half of men. These men may then be subject to chronic inflammation without realising it.

The study found that in the laboratory setting, the protein from the parasite acted on human blood cells and benign and cancerous prostate cells in a similar way to the human protein. The researchers conclude that infection with the parasite, in combination with other factors, might trigger inflammatory pathways that could lead to cancer growth.

It is important to note that this early study did not involve any men with benign enlargement of the prostate or prostate cancer. Further research will be required to investigate whether there is a clear link between trichomoniasis and prostate cancer.

It could be the case that trichomoniasis is just one of a series of risk factors rather than a single definitive cause.

Where did the story come from?

The study was carried out by researchers from the University of California, Los Angeles, the Università degli Sutdi di Sassari, Italy and the Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomύs, Argentina. It was funded by the National Institutes of Health Grants, the Microbial Pathogenesis Training Grant, a Warsaw Fellowship, a Graduate Division Dissertation Year Fellowship, a Medical Scientist Training Program Grant, Fondazione Banco di Sardegna Grant and a Regione Autonoma della Sardegna Grant. 

No conflicts of interest were reported.

The study was published in the peer-reviewed medical journal PNAS.

While the general content of the reporting by BBC News and The Independent was accurate, their headlines (“Prostate cancer ‘may be a sexually transmitted disease’”) were probably a bit over-the-top given the preliminary nature of the research. Though both organisations included quotes from Cancer Research UK pointing out that it is too early to add prostate cancer to the list of cancers that have been found to have an infectious cause, such as cervical cancer.

We cannot say with any conviction that prostate cancer is a sexually transmitted infection. Other known risk factors for prostate cancer include age, ethnicity and family history. This arguably suggests that the disease may arise due to a combination of complex risk factors.

Links To The Headlines

Prostate cancer ‘may be a sexually transmitted disease’. BBC News, May 20 2014

Prostate cancer ‘could be a sexually transmitted disease’, scientists say. The Independent, May 20 2014

Links To Science

Twu O, Dessi D, Vu A, et al. Trichomonas vaginalis homolog of macrophage migration inhibitory factor induces prostate cell growth, invasiveness, and inflammatory responses. PNAS. Published online May 19 2014