Tehran University of Medical Sciences Basic & Clinical Cancer Research 2228-6527 9 4 2018 04 07 4 12 EN Azar Esfahbodi M.Sc graduated in SportsPhysiology, Faculty of physicaleducation and sport sciences, Islamic Azad University, Bojnord, Iran. Mehrdad Fathi Associate Professor ofDepartment of Sports Physiology,Faculty of physical education and sport sciences, Ferdowsi University of Mashhad, Mashhad, Iran. Gholam Rasul Mohammad Rahimi Ph.D. Student in SportsPhysiology, Faculty of physical education and sport sciencesFerdowsi university of Mashhad, Mashhad, Iran. 2017 07 28 2018 02 28 Background: Exercise has positive effects on breast cancer evolution, including prevention, medical treatment, and aftercare clinical settings. Plus, elevated serum levels of CEA and CA15-3 as prognostic indicators were identified in patients with breast cancer. So, this study aimed to investigate the changes of CEA and CA15-3 biomarkers in the breast cancer patients following eight weeks of aerobic exercise. Methods: In this quasi-experimental study, 15 females with breast cancer with mean age (44.46±17.15 years), weight (70.53±5.18 kg) and body mass index (27.58±2.18 kg/m2) were randomly selected and performed aerobic training (for 8 weeks,3 sessions per week, with an intensity of 30%-60% heart rate reserve). Before and after the intervention, while all patients were fasting for 12 hours, the levels of CEA and CA15-3 were measured. The data obtained were analyzed, using paired sample t-test at a significance level of P<0.05. Results: Findings showed that the tumor marker (CA15-3) decreased following 8 weeks of aerobic exercise although it was not significant (P=0.091); CEA level did not change significantly after exercise, either (P=0.542), but a significant decrease was observed in body mass index, body fat percentage and weight values after exercise (p=0.001).  Conclusion: Elevated CA15-3 and CEA which are considered as the diagnosis of metastatic breast cancer was not observed in the study. Exercise could reduce CA15- 3 insignificantly. Also, aerobic exercise for eight weeks improved body composition indices, without increasing the level of fatigue or stress values, which may contribute to the prevention of the cancer prevalence in middle-aged women. https://bccr.tums.ac.ir/index.php/bccrj/article/view/243 https://bccr.tums.ac.ir/index.php/bccrj/article/download/243/03