Quoted from http://www.nytimes.com/2010/10/20/health/20hormone.html
Breast Cancer Seen as Riskier With Hormone
By DENISE GRADY
Published: October 19, 2010
Hormone treatment after menopause, already known to increase the risk of breast cancer, also makes it more likely that the cancer will be advanced and deadly, a study finds.
Women who took hormones and developed breast cancer were more likely to have cancerous lymph nodes, a sign of more advanced disease, and were more likely to die from the disease than were breast cancer patients who had never taken hormones.
The increased risks were relatively small and are not fully understood. But previous research has found that hormone treatment can cause delays in diagnosis by increasing breast density, making tumors harder to see on mammograms. Delayed diagnosis may increase the risk of death.
It is also possible that hormones may feed the growth of some breast cancers or the blood vessels that tumors need to grow and spread.
The treatment studied was the most commonly prescribed hormone replacement pill, Prempro, which contains estrogens from horse urine and a synthetic relative of the hormone progesterone.