While there is a general belief that hormone replacement therapy increases the risk of recurrence of breast cancer, there is in fact no hard data to prove this notion. Indirect evidence is provided, however, from observations on the effect of obesity on risk of breast cancer recurrence. This is because obesity is associated in postmenopausal women with increased circulating estrogen levels and obesity is also associated with lower sex hormone binding globulin levels so that the levels of non-SHBG bound estradiol are further increased.