Antimetastatic effect of the liposomal form of recombinant lactaptin RL2 (a proteolytic fragment of human breast milk κ-casein; 8.6 kDa) was studied in A/Sn mice after intravenous transplantation of GA-1 tumor with high rate of liver metastases. Tumor growth in the liver was found in all mice. In animals dying early, the tumors were presented by multiple nodes of about the same size; in mice dying later, the tumors in the liver were presented by just few large nodes formed by cells that survived chemotherapy. A single intravenous injection of RL2 lactaptin in liposomes prolonged lifespan of animals with liver metastases of GA-1 tumor by 1.5 times in comparison with that in untreated animals.