Given the theoretical considerations, (increased strength of the hydrogen link of deuterated compounds, changes in the speed and directions of biochemical reactions, distortion of the regulation and division of cells and some others), it can be assumed that replacing the deuterium in the body with a light-weight isotope results in the normalization of biochemical reactions, the improvement of the functioning of the immune system and, consequently, in the suppression of the tumorigenesis and metastatic disease.