A genetically engineered analog of human kappa casein was developed and obtained. It has been found to have the ability to induce apoptosis of human cancer cells in culture and inhibit the growth and metastasis of animal and human tumors. Based on the recombinant protein obtained, a new antitumor drug RAHMP (recombinant analogs of human milk peptides) has been developed, which is a concentrate for the preparation of an infusion solution. The main function of this drug is prevention and treatment of human breast cancer. The purpose of this work was to develop and validate a technique for the quantitative determination of impurities in the RAHMP substance by reverse-phase high-performance liquid chromatography. Criteria for assessing the quality of the substance were the area of the main peak, which should be at least 95% of the total area of all detected peaks, and the sum of the areas of additional peaks should be no more than 5% of the total area of all peaks. The permissible content of foreign impurities in the substance should be no more than 5%. The relative standard deviation of the impurity concentration at all levels of the concentrations under consideration does not exceed 2.0%, which indicates satisfactory convergence of the results.