OBJECTIVES: Digit ratio, especially second-to-fourth digit ratio (2D:4D) is 
established in utero and is positively correlated with oestrogen in men and 
women. It is a putative biomarker for prenatal hormone exposure and may 
represent an individual predisposition to certain diseases (e.g., breast 
cancer). The aim of the present study is to investigate whether there is a link 
between digit ratio (2D:4D) and breast cancer in Chinese populations.
METHODS: The controls we chose were healthy subjects-age and -sex matched to the 
patients diagnosed with breast cancer. Photocopies of the two hands of 218 women 
(controls: 109; patients: 109) were collected. Left hand, right hand, mean hand, 
and right minus left 2D:4D (Dr-l ) were analyzed.
RESULTS: The patients with breast cancer presented significantly higher 2D:4D 
than controls (left: P < 0.01; right: P < 0.05; mean: P < 0.05). The mean values 
of 2D:4D on the left hand were significantly higher than those on the right hand 
in the two groups, respectively (controls: P < 0.05; patients: P ≤ 0.01). In 
patients, there was a significantly negative correlation between 2D:4D (left 
hand: P < 0.01; right hand, mean: P < 0.05) and the presented age with breast 
cancer, but no association between Dr-l and age of presented disease.
CONCLUSIONS: Digit ratio (2D:4D) may correlate with the increased risk of breast 
cancer.