19th CENTURY MEDICINE

NEW YORK (Reuters Health) Aug 30 - Finger length - specifically, the ratio of the second to fourth digits -- might be a predictor of prostate cancer risk, according to a recent study from Korea.

Men with a digit ratio below 0.95 had higher average prostate-specific antigen (PSA) levels and higher prostate cancer risks than men with larger ratios.

But the sample size was small (366 men) and the results, which appeared online July 13th in BJU International, must be interpreted with caution and confirmed, experts warn.

Lead author Dr. Han Jung and his colleagues from the Gachon University Gil Hospital in Incheon, Korea, measured the second to fourth digit ratio (using digital vernier calipers), prostate volume, and PSA and testosterone levels in men age 40 and older with lower urinary tract symptoms. Those with PSA levels of 3 ng/mL or more had prostate biopsies.

Out of the 366 patients, 89 had PSA levels high enough to warrant a biopsy, and 28 of those were diagnosed with prostate cancer. There was no relationship between digit ratio and prostate volume, but lower digit ratios were associated with higher PSA levels (r = -0.140, P = 0.007).

When patients were divided into groups, one with digit ratios below 0.95 and the other with ratios equal to or above 0.95, the lower ratio group had higher mean PSA levels (3.26 vs. 1.89 ng/mL) and a higher overall rate of prostate cancer (11.4% vs. 3.8%) than the higher ratio group. There was no difference in age, testosterone level, or prostate volume between the two groups.

The results suggest that prenatal androgen exposure, known to be negatively associated with digit ratios, may predict PSA levels and prostate cancer risk, the authors say. Prenatal androgen exposure in black people, who have been shown to have lower digit ratios on average than white people, could help explain why black men are 2.5 times more likely to die of prostate cancer than white men, they add.

Dr. John Manning, a psychologist at Swansea University in Wales who is an expert on digit ratios, praised the study's authors for measuring digit lengths directly with calipers, instead of through photocopies, which can produce inaccurate readings, he said. Although he has also suggested a possible link between prenatal testosterone and prostate cancer risk, he cautioned against reading too much into the findings.

"This is only one study with a relatively small sample," he told Reuters Health by email. "We need to see it repeated with larger samples and in other ethnic groups."

Even if the finding is confirmed, it would only reflect average trends across a population, and shouldn't be used to assess an individual's risk of prostate cancer, according to Dr. Marc Breedlove, a neuroscientist at Michigan State University.

"If digit ratios correlate with prostate cancer risk, that does indeed indicate that individual differences in exposure to androgens early in life affect the likelihood of prostate cancer in adulthood," Dr. Breedlove told Reuters Health by email. "But I very much doubt whether that correlation could be used to accurately predict the probability that a particular person will or will not contract prostate cancer."

BJU Int. Posted online July 13, 2010. Abstract