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In the years leading up to the advent of the Gardasil vaccine, awareness grew about human papillomavirus, or HPV. HPV is a sexually transmitted infection (STI) that is a risk factor for cancer when you are infected with certain strains—primarily cervical cancer in women, penile cancer in men, and throat and anal cancer in both sexes. But did you know another STI has been linked to cancer, strictly in men? About a decade ago, researchers began investigating whether Trichomonas vaginalis — a parasite that causes the common STI trichomoniasis — could lead to prostate cancer.
- Studies have found that inflammation in the prostate may increase prostate cancer risk.
- Trichomoniasis—the most common curable STI—can cause inflammation in both the urethra and the prostate.
- Trichomonas vaginalis, the parasite that causes trichomoniasis, secretes a protein that has been found to increase the growth rate of benign and cancerous prostate cells.
- An investigation into whether infection with trichomonas vaginalis was associated with a higher risk of dying from prostate cancer did not find a link.
What is Trichomoniasis?
Trichomoniasis—or trich—is one of the most common sexually transmitted Infections, with about 3.7 million (CDC, 2017) estimated cases in the US each year. It’s caused by Trichomonas vaginalis (T. vaginalis), a single-celled microscopic organism that passes from the penis to vagina, vagina to the penis, or vagina to vagina during sex.
Up to 70 percent of those infected show no symptoms and can carry trich around for years. According to the CDC, some men with trich might feel itching or irritation inside the penis; a burning sensation after urination or ejaculation, or have a discharge from the penis. Women are more likely to be infected. Their symptoms include itching, burning or soreness of the genitals, pain during urination, or genital discharge.
The infection can be quickly and easily cleared up with antibiotics. According to the CDC, it’s the most common curable STI (CDC, 2017).
What is prostate cancer?
Prostate cancer is the most common cancer in men behind skin cancers. The American Cancer Society estimates that 174,650 men in the US will receive a prostate cancer diagnosis in 2019, and 31,620 men will die from the disease (ACS, 2019).
Prostate cancer develops in the prostate gland, a walnut-sized organ that sits between the bladder and the penis, right in front of the rectum. The prostate produces prostatic fluid, which helps nourish and transport sperm during ejaculation.
According to the American Cancer Society, it’s not clear what causes prostate cancer (ACS, 2019), but some studies (Sfanos, 2011) have suggested that chronic inflammation of the prostate may be one culprit.
That’s where T. vaginalis comes in. Trich can cause inflammation in the urethra or the prostate, also known as urethritis and prostatitis, respectively.
What is the link between Trichomonas vaginalis and prostate cancer?
In a 2014 study (Twu, 2014), researchers from UCLA and the University of Sassari in Italy found that T. vaginalis secretes a protein that promotes inflammation and increases the growth rate of benign and cancerous prostate cells in vitro.
The findings come after a 2009 study that looked into the link between trich and prostate cancer (Stark, 2009). In that study’s sample, 25 percent of men who had been diagnosed with prostate cancer also tested positive for T. vaginalis, compared to 21% of men without prostate cancer who tested positive. This result was not statistically significant. However, researchers found that they infected men with prostate cancer were more than twice as likely to develop an aggressive form of prostate cancer that spread outside the prostate.
“This study suggests a possible way the parasite Trichomonas vaginalis could encourage prostate cancer cells to grow and develop more quickly,” said Nicola Smith, health information officer at Cancer Research UK, about the 2009 research (Roberts, 2014).
But the studies didn’t prove a cause-and-effect link between trich and prostate cancer. “The research was only done in the lab,” said Smith, “and previous evidence in patients failed to show a clear link between prostate cancer and this common sexually transmitted infection.”
A study published in the International Journal of Cancer investigated whether infection with T. vaginalis was associated with a higher risk of dying from prostate cancer; the researchers didn’t find a link (Tsang, 2018).
Those are the only three studies that have examined the association between trich and prostate cancer, said the authors of a 2019 review published in the World Journal of Oncology (Rawla, 2019). They theorized that T. vaginalis’s “frequent asymptomatic presentation may make it possible to persist untreated and ascend to the prostate, where it can establish foci of chronic inflammation that may eventually lead to prostate cancer.”
So what can you do?
Although we don’t definitively know that Trichomoniasis can raise your risk of prostate cancer, if you’ve got trich, the move is to clear it up ASAP. Get regular screenings for STIs, and make sure to ask your healthcare provider to include trich as part of your screening, because it is not routinely checked with the other STIs
And while science isn’t sure how you can prevent prostate cancer, research suggests there are easy things you can do to lower your risk. These tactics include limiting your intake of high-fat foods, adding more fruits and vegetables to your diet, and exercising regularly. If you have a family history of prostate cancer or are African-American, the American Cancer Society recommends discussing being screened for prostate cancer with your healthcare provider at age 45. They also recommend that men of average risk should have that talk at age 50 (ACS, 2019).