Objective: To compare the effectiveness of oral progestins and injectable gonadotropin-releasing hormone antagonist medication in cancer fertility preservation in patients with breast cancer. Methods: A cross-sectional study with 40 breast cancer patients submitted to cancer fertility preservation, who were divided into two groups according to histochemical analysis of progesterone receptors to define luteinizing hormone block: if positive, use of gonadotropin-releasing hormone antagonist, if negative, use of oral progestins. The mean age, medication days, antral follicle count, number of oocytes in metaphase II and the occurrence of ovarian hyperstimulation syndrome were compared. Results: A total of 20 patients both in the group using gonadotropin-releasing hormone antagonist, and in the group with oral progestins, respectively, had a mean age of 33.9 (32-35.8) and 33.8 (32-35.6) years; days of medications of 11 (9.7-12.3) and 12.8 (11.6-13.9), p=0.037; antral follicle count of 9 (7.11-12) and 8.5 (6-11.9), p=0.370; metaphase II oocyte number of 4 (2.1-9.8) and 7.5 (3.1-10), p=0.348; and ovarian hyperstimulation syndrome of 2 (10%) and 5 (25%) cases, p=0.212. Conclusion: The use of oral progestins, in spite of requiring longer treatment time, is effective in relation to the protocol with gonadotropin-releasing hormone antagonist, and offers greater comfort at a lower cost in breast cancer patients with negative progesterone receptors, submitted to cancer fertility preservation.