The present invention relates to: a pharmaceutical composition for treating cancer containing, as an active ingredient, a metal lactate salt, which can be dissociated, in cancer cells, into lactate capable of effectively inhibiting actions such as proliferation, invasion, and metastasis of cancer cells by disturbing the metabolic processes of cancer cells; a pharmaceutical composition for inhibiting cancer metastasis; a food composition for alleviating cancer; and a method for treating cancer and a method for inhibiting cancer metastasis, both methods comprising a step of administering the lactate metal salt. The metal lactate salts of the present invention inhibits the growth of cancer cells and induces the death of cancer cells by disturbing the metabolic processes in the main energy production pathways of cancer, and inhibits the expression of factors inducing resistance against radiation exposure, while having no side effects. Therefore, the lactate metal salt can be widely utilized in a more effective anti-cancer therapy.