KLRK1 and neoplasm: Taking into account the blood volumes of infants (85 ml/kg) and adults (65 ml/kg) and the serum half-life of soluble NKG2D ligands of 6 days [59], the tumor mass required to account for the plasma levels of soluble NKG2DLs in patients can be estimated to tumor spheres with a diameter of 5.9 - 17.8 mm and 10.9 - 32.7 mm, respectively.