Taking an oral bisphosphonate* is probably associated with a decreased risk of endometrial cancer. The protective effect has been seen in women who take an oral bisphosphonate for more than one year. Oral bisphosphonates are usually taken by older women. The protective effect of oral bisphosphonates has been reported mainly in studies involving women who have reached menopause, but the effect may also occur in younger women. 

The longer a woman uses an oral bisphosphonate, the lower her risk of endometrial cancer becomes. In women taking an oral bisphosphonate for between 1 and 3 years, the risk of endometrial cancer has been shown to be 42% lower than in women who have never used this type of medicine. The risk is 66% lower in women who have used an oral bisphosphonate for more than 3 years.

The protective effects of bisphosphonates may be due to their effects on how cells grow and divide and possible effects on the immune system.

*Oral bisphosphonates are medicines used to treat osteoporosis.