Can finger length predict prostate cancer risk?

Men’s Health Mythbuster is a section on UrologyTimes.com that explores common statements and beliefs about men’s health and evaluates whether these statements are false.

Mr. Lawlor and Mr. Miller are research assistants and Dr. Albala is medical director at Associated Medical Professionals, Syracuse, NY.

Can the length of a person’s finger tell you anything about their risk for developing prostate cancer?

Although not many have investigated the link between finger length and prostate cancer, there are several studies that have found significant relationships between finger length and the incidence of prostate cancer (BJU Int 2011; 107:591-6; Br J Cancer 2011; 104:175-7). These studies largely focus on the ratio of index finger length (2D) relative to ring finger length (4D). It has been suggested that this 2D:4D ratio can be used as a marker of prenatal androgen exposure (J Biosoc Sci 2007; 39:599-612), with a low 2D:4D ratio being associated with high prenatal testosterone exposure (BJU Int 2011; 107:591-6). In other words, lower prenatal testosterone exposure is associated with a higher likelihood of having longer index fingers, and possibly a reduced likelihood of developing prostate cancer (BJU Int 2011; 107:591-6; Br J Cancer 2011; 104:175-7).

A study published in the British Journal of Cancer collected data over 15 years from 1,524 patients with prostate cancer and 3,044 patients without known prostate cancer. Participants were asked to identify their 2D:4D ratio by comparing their hand pattern to a series of pictures depicting an index finger either shorter than, equal to, or longer than a ring finger. Participants with a greater 2D:4D ratio were found to have a significantly decreased prostate cancer risk than participants with lower 2D:4D ratios (Br J Cancer 2011; 104:175-7).

These findings mimic findings of a similar study that investigated finger length, prostate volume, prostate cancer risk, and PSA values. This study recruited 366 men to undergo a transrectal ultrasound of the prostate, as well as a 12-core prostate biopsy if their PSA value was ≥3 ng/mL. The participants’ digit ratios were measured with calipers (BJU Int 2011; 107:591-6). While no association was found between digit ratio and prostate volume, lower digit ratios were associated with greater PSA values, greater PSA density, greater risk of undergoing prostate biopsy due to elevated PSA, and a greater risk of having prostate cancer (BJU Int 2011; 107:591-6).

However, a study published in the British Journal of Cancer denied the existence of a correlation between 2D:4D ratio and prostate cancer. For the study, 6,258 men participating in the Melbourne Collaborative Cohort Study had their 2D:4D ratio evaluated. Among these men, 686 incident prostate cancer cases were identified. Hazard ratios (HRs) and confidence intervals (CIs) were estimated for a standard deviation increase in 2D:4D ratio. No correlation was detected between 2D:4D ratio (for either hand) and prostate cancer risk overall (HRs 1.00; 95% CIs, 0.92–1.08 for right, 0.93–1.08 for left) (Br J Cancer 2011; 105:438-40).

Next:"Proposed explanations for a link between digit ratio and prostate cancer risk have had equally mixed results"Proposed explanations for a link between digit ratio and prostate cancer risk have had equally mixed results. Some studies showing support for a link between the 2D:4D ratio and prostate cancer risk have stated that high prenatal androgen exposure may be to blame (BJU Int 2011; 107:591-6; Br J Cancer 2011; 104:175-7). However, this hypothesis has yet to be strongly supported. Additionally, prior studies investigating prostate cancer patients in adulthood somewhat challenge this connection. Although prostate cancer is known to be hormonally driven and regulated, studies have failed to identify a relationship between a single measure of hormone levels in adulthood and the risk of developing prostate cancer (Br J Cancer 2011; 105:438-40).

Some studies have suggested the number of cytosine-adenine-guanine (CAG) repeats in the androgen receptor gene (AR) as a possible link. It has been well established that fewer CAG repeats in the AR gene increases the risk of prostate cancer. Recently, a meta-analysis of studies linking short CAG repeats to an increased risk of prostate cancer was published in Scientific Reports (2017; 7:40554). The study reviewed 51 publications with 61 studies and results showed that short CAG repeats (<22 repeats) carriers presented an increased risk of prostate cancer compared with long CAG repeats (≥22 repeats) carriers (OR=1.31, 95% CI 1.16 to 1.47). Prostate cancer cases were shown, on average, to have fewer CAG repeats (MD = −0.85, 95% CI −1.28 to −0.42) than controls. This finding that fewer CAG repeats may indicate increased risk of prostate cancer is intriguing, but do CAG repeats also relate to the 2D:4D ratio?

A study published in Evolution and Human Behavior demonstrated that the digit ratio of the right hand was positively correlated with the number of CAG repeats on the AR gene, and men with a low 2D:4D ratio have AR genes with fewer CAG repeats (Evol Hum Behav 2003; 24:399-405). However, the study by Manning et al was conducted using only 50 individuals, and has since been replicated with a much larger sample size (N=157). The study with the larger sample size (sufficient to detect a positive correlation as strong as that reported by Manning with >90% power or to detect a correlation even two thirds its size with ∼80% power, at α=.05) failed to reproduce the correlation between digit ratio and short CAG repeats on the AR gene found by Manning et al (Evol Hum Behav 2012; 33:557-61). To further dispel the findings of the Manning et al study, a meta-analysis of 18 studies linking CAG repeats and digit ratio concluded that the number of CAG repeats on the AR gene is unrelated to 2D:4D digit ratio (Evol Hum Behav 2014; 35:430-7).

Ultimately, no overwhelming evidence exists to support a link between prostate cancer risk and digit length.

Section Editor Steven A. Kaplan, MD, is professor of urology at Icahn School of Medicine at Mount Sinai and director of benign urologic diseases at Mount Sinai Health System, New York. Follow him on Twitter at @MaleHealthDoc.