Does having an enlarged prostate doom you to prostate cancer?

Far from it, a new study suggests.

Also called benign prostatic hyperplasia (BPH), the condition may actually provide some protection for men from developing prostate cancer, researchers report.

"Men are often anxious about prostate cancer, as it is the second most common cancer in men, with some worrying BPH increases their risk of prostate cancer," said lead researcher Dr. Kiran Nandalur. He is vice chief of diagnostic radiology and molecular imaging at Beaumont Hospital in Royal Oak, Mich.

"Some previous studies have demonstrated BPH may increase the risk of cancer, given common driving forces such as genetics, hormones and inflammation. Our study should alleviate their concern, as BPH may decrease their odds of prostate cancer," Nandalur said.

BPH is common in aging men and can cause a frequent need to urinate, often at night, or a weak flow of urine. This is because the central part of the prostate enlarges and can block urine from leaving the bladder.

Surprisingly, as the prostate continues to enlarge, the odds of prostate cancer goes down, Nandalur explained.

"Moreover, BPH decreases the odds of not just a single focus of cancer, but also more than one site. Based on these findings, BPH may be producing mechanical pressure throughout the gland, which inhibits cancer growth and decreases the odds of prostate cancer," he added.

For the study, Nandalur's team collected data on 405 men with BPH and looked for evidence of prostate cancer on MRIs of prostate tissue.

The researchers found that as the size of the prostate increased, the risk of prostate cancer decreased. For every one cubic centimeter increase in the volume of the prostate, the risk for prostate cancer dropped by about 3%, they noted.

"The size of the central gland from BPH may help to stratify risk for patients with prostate cancer," Nandalur said. "Currently, prostate cancer patients are categorized into low, intermediate and high risk, with central gland contributions not taken into account. In the future, the degree of BPH as measured on prostate MRI may also be contributory to help determine prognosis and the course of therapy."

Some commonly used BPH drugs called 5-alpha-reductase inhibitors—including finasteride (Proscar)—decrease the size of the prostate, and have a U.S. Food and Drug Administration drug safety warning because they have been found to increase the risk of high-grade prostate cancer, Nandalur noted.

"Our study finds a potential explanation for the findings, as decreasing the prostate size with these drugs may lead to decreased pressure throughout the gland and possibly allow cancer to grow. These are very useful drugs to treat BPH, but care should be taken," Nandalur said.

Dr. Anthony D'Amico, a professor of radiation oncology at Harvard Medical School in Boston, said that he would take these study results with a grain of salt.

"I would approach this with extreme caution," D'Amico said.

These findings could result because BPH makes cancer harder to find with a biopsy, D'Amico said. "BPH could make it harder to find cancer because your needle is now going into a much smaller area. So I think it's interesting, there may be something there, but certainly not something that I would call conclusive at this time," he explained.

The findings may, however, have a biological explanation, he said. "If you have a lot of BPH, that's competing with prostate cancer for growth factor, maybe the prostate cancer gets a growth disadvantage," D'Amico said. "That's a biological premise, but it's not been proven."

D'Amico advises men with BPH to have an MRI and biopsy to be sure there isn't cancer.

"If you have a large prostate I would not assume that any prostate cancer you have is going to be clinically insignificant. You should still have an MRI and a fusion biopsy to rule out clinically significant disease," he said. "This study is interesting, but not conclusive."

The report was published online Aug. 10 in the journal The Prostate.

—Steven Reinberg Healthday Reporter