Association between digit ratio (2D:4D) and right-left difference in 2D:4D ratio with breast cancer risk: multicentre case-control study from India.

Recently, the second to fourth fingers/digits ratio (2D:4D) has been reported to be associated with breast cancer (BC). We aimed to assess whether this association exists in Indian population. We derived the 2D:4D of right and left-hand from length of the index and ring finger, measured using Vernier callipers. We also calculated the right minus left 2D:4D (DR−L). For 1638 BC cases and 1723 controls, univariate unconditional logistic regression model was used to estimate odds ratio (OR) with its corresponding 95% confidence interval (CI). We observed reduced risk of BC with increase in right 2D:4D in pre- menopausal women (OR: 0.71, 95% CI: 0.52–0.96), while for post-menopausal women there was non-significant positive association. For left 2D:4D, non-significant slight increased risk of BC was observed in the highest category amongst the premenopausal women (OR: 1.12, 95% CI: 0.82–1.52). For DR−L we observed inverse association in pre-menopausal women only (OR: 0.73, 95% CI: 0.58–0.92). The association between the 2D:4D ratio and BC risk was weak and inconsistent across pre-/post-menopausal groups. Larger and more precise studies with longitudinal follow-up, and reduced random measurement error are needed to clarify whether a clinically meaningful 2D:4D ratio threshold can reliably predict BC risk.