Background & aim: Breast cancer is the most common type of cancer and the most common cause of death in middle-aged women in developed countries.  The results have indicated that sedentariness and hormonal changes increase the risk of breast cancer. The aim of the present study was to evaluate the effect of eight weeks of aerobic training on levels of growth hormone and 17-beta estradiol middle-aged women with breast cancer.

Methods: In the present semi-experimental study, 15 women with breast cancer with the mean age of 44.46±17.15 years, weight (70.53±5.18 kg) and body mass index (27.58±2.18 kg/m²) were selected through available sampling and considered as the experimental group. The exercise program was performed three sessions per week, and every session lasting 40-60 minutes with an intensity of 30%-60% heart rate reserve (HRR) for eight weeks. Growth hormone and beta 17 estradiol levels pre and post aerobic training, 12 hrs of fasting and with 24 hrs of severe Lack of physical activity was measured during of eight weeks. Data were analyzed by paired samples t-test at a significance levels of P<0.05.

Results: The growth hormone levels did not change significantly after eight weeks of aerobic exercise (P=0.447), whereas 17-beta estradiol levels decreased significantly (P=0.000).

Conclusion: It seemed that eight weeks of aerobic exercise could reduce one of the breast cancer markers (17-beta estradiol); so these training are recommended for the improving or prevention of breast cancer.