On the one hand, the different ranges obtained by these assays might be explained by the diverse BC cohorts analyzed, on the other hand by the existence of monomers/dimers and tetramers of TK1 24,45 and the existence of TK2 (related protein – mostly in mitochondria and with other substrate spectrum and kinetics45) which might be detected with one but not the other test. This evidence concerns the gene TK2 and breast cancer.