The second to fourth digit ratio (2D:4D): A risk factor of bladder cancer in men

Background: Exposure to prenatal sex steroids as indicated by the ratio of the second to fourth digit length (2D:4D) has been linked to the risk of onset of cancer, while sex steroids may expand the gender disparity in bladder cancer (BC) morbidity. Aim: To explore the association between 2D:4D ratio and BC risk. Subjects: 307 bladder cancer patients and 321 cancer-free individuals. Outcome measures: Relationships between 2D:4D and incidence of bladder cancer. Results: For males, a lower 2D:4D ratio of both hands was obtained in the BC group, relative to the control group (left hand: 0.940 +/- 0.031 vs. 0.954 +/- 0.024, t = -4.72, p < 0.001, Cohen'sd = 0.491 and right hand: 0.939 +/- 0.031 vs. 0.952 +/- 0.022, t = -4.493, p < 0.001, Cohen'sd = 0.511). In females, no differences in the 2D:4D ratio were observed between the BC and control groups (p > 0.05). Correlation analysis between 2D:4D ratio and pathological index found no correlation among the BC grade or stage (p > 0.05). Conclusion: Men with BC have a lower 2D:4D ratio compared with healthy men. Therefore, having a low 2D:4D ratio is a risk factor for BC in men. Prenatal exposure to sex steroids might play a role in the etiology of BC, which could partially explain the gender disparity in the prevalence of BC.