No associations were observed for Dr-l (data not shown). Estimated HRs did not vary substantially by tumour aggressiveness ( Table 2). The HRs for an increase of one standard deviation in 2D:4D and risk of prostate cancer for age <60 years were 0.91 (95% CI, 0.73–1.13) and 0.88 (95% CI, 0.71–1.10) for left and right hands, respectively. Splitting follow-up at an age of 60 years and estimating separate HRs for the two age brackets also suggests that higher 2D:4D might be associated with decreased prostate cancer risk before 60 years of age. Similarly, risk of prostate cancer for men older than 80 years appears to be slightly reduced with higher 2D:4D however, CIs include unity for all observed ages. For instance, the HR for an increase of one standard deviation in 2D:4D and prostate cancer risk at an age of 55 years is ≈0.80 (95% CI, ≈0.65–1.10) for both hands. There is some indication that higher 2D:4D is associated with lower early onset prostate cancer risk. Estimated age-varying HRs and 95% CIs are plotted in Figure 1. We found no overall association between either left or right 2D:4D and prostate cancer risk (HRs 1.00 95% CIs, 0.92–1.08 for right, 0.93–1.08 for left). Statistical analyses were performed using Stata 11.1 for Linux (Stata Corporation, College Station, TX, USA).ĪTwo men were missing information on baseline smoking status.Įstimates from Weibull models are presented in Table 2. Separate models were fit for right and left 2D:4D and Dr-l, and all models were adjusted for country of birth and baseline smoking status, as these factors are associated with 2D:4D ( Manning et al, 2000 Manning and Fink, 2011). Separate estimates of HRs and CIs for age 7 or stage IV, or having prostate cancer as cause of death. Knots were evenly spaced across the distribution of uncensored log survival times. Age-varying HRs were estimated by flexible parametric survival models ( Lambert and Royston, 2009), incorporating restricted cubic splines with six knots to model the baseline hazard, and restricted cubic splines with one knot to allow the HR to vary with age. Overall hazard ratios (HRs) and 95% confidence intervals (CIs) for a standard deviation (s.d.) increase in 2D:4D measures were obtained from Weibull models with age as the time axis. During a median follow-up of 16 years, 686 incident prostate cancer cases were identified via linkage to the Victorian Cancer Registry. Of 6287 men who attended follow-up, we excluded 29 with a pre-baseline diagnosis of invasive prostate cancer or unknown primary tumour, leaving 6258 men available for analysis. Measurement was undertaken by a team of trained research assistants at Cancer Council Victoria.įollow-up commenced at baseline attendance and ended at 30 June 2009, the date the participant left Australia, diagnosis of an unknown primary tumour, or death, whichever occurred first. The length of the index finger was divided by the length of the ring finger to obtain 2D:4D, and Dr-l was defined as the difference between right and left 2D:4D. The length of the index and ring fingers were measured from photocopies of the surface of the hand using digital Vernier calipers. At a recent face-to-face follow-up conducted during 2003–2009, 6287 men had their hands photocopied. Details of the MCCS have been published previously ( Giles and English, 2002). The MCCS is a prospective cohort study of 41 514 people (17 045 men) recruited between 19, 99.3% of whom were aged 40–69 years. We examine whether 2D:4D is associated with prostate cancer risk in a large sample of men participating in the Melbourne Collaborative Cohort Study (MCCS). Both of these studies concluded that low 2D:4D, and thereby high prenatal testosterone, is a marker of increased risk of prostate cancer. Two recent studies have aimed to assess whether 2D:4D is associated with prostate cancer ( Jung et al, 2011 Rahman et al, 2011). Prostate cancer is a hormonally driven and a regulated disease, but studies have failed to detect associations between a single measure of hormone levels in adulthood and prostate cancer risk ( Roddam et al, 2008). Hormone exposure in early life has been implicated in the aetiology of numerous cancers ( Potischman et al, 2005). There are several lines of evidence indicating that 2D:4D is affected by prenatal androgens ( Breedlove, 2010), and that digit ratios are longitudinally stable ( McIntyre et al, 2005 Trivers et al, 2006). The ratio of the lengths of the index (2D) and ring (4D) fingers as measured by the ratio 2D:4D has been suggested as a proxy indicator of prenatal androgen activity, with low 2D:4D reflecting higher in utero testosterone exposure ( Manning et al, 1998 McIntyre, 2006 Hönekopp and Watson, 2010).
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