Hi - I think you're a bit confused. Estrogen isn't the cause of cancer. It helps certain breast cancers grow, so it definitely stimulates some cancers; but it doesn't cause cancer. Unfortunately, no one knows the cause of cancer; if we did, we'd probably have a cure by now! Your risk for getting breast cancer can be increased by genetic abnormalities; by age; by dense breasts; by family history; and by other factors. But about 85% of women who get breast cancer have no known risk factors... so it's pretty random. I hope you've been tested for the HER2-neu protein, because if you're positive, you can take drugs to help prevent a recurrence. Best of luck to you - PJH