TK1 and breast cancer: In a study in which investigators compared serum TK1 activity between healthy subjects and patients with breast cancer, the median and IQR value for TK1 activity activity was 16 Du/L (IQR 9–33 Du/L) in the healthy blood donors (n = 149) and moderately increased in patients with primary breast cancer prior to surgical exicision (n=160), with median level of 37 Du/L (IQR 20–92 Du/L), respectively. [6].