MIAMI, Mar 08 (Reuters Health) - Whether hormone replacement therapy (HRT) is safe for breast cancer survivors is still unclear, and the concurrent use of tamoxifen is currently being studied.Presentations raising the question of HRT safety after breast cancer were made here during the 17th annual Miami Breast Cancer Conference.

In women using HRT, estrogen could stimulate growth of estrogen receptor-positive breast cancers, Dr. Melody A. Cobleigh from the Rush Cancer Institute in Chicago, Illinois, told the audience.Because estrogen also increases the level of progesterone receptors, "HRT users would be expected to be more likely to develop progesterone receptor-positive breast cancers."

Her group studied 306 postmenopausal women with breast cancer who were using HRT within 1 month of diagnosis compared with women who had never used HRT.They found no differences in tumor size, nodal status, or levels of estrogen receptors between groups.

However, women using HRT were significantly more likely to be positive for progesterone receptors and have a high fraction of cells in S-phase.Among the estrogen receptor-positive tumors, "HRT was really having a biological effect on the tumor," she said.About 50% of women using HRT had a high fraction of cells in S-phase, compared with only 20% of women who never used HRT.

"S-phase in [estrogen] receptor-positive tumors should be interpreted in light of HRT use," she concluded.

Tamoxifen may block the cancer-promoting effect of estrogen and thus block dormant tumor cells from HRT stimulation, Dr. Cobleigh said, and this point is being studied in the Eastern Cooperative Oncology Group trial.Breast cancer survivors taking tamoxifen will be randomized to HRT or placebo to relieve hot flashes and study various endpoints.

Dr. Kathleen I. Pritchard of the University of Toronto in Ontario, Canada, pointed out that the data regarding HRT right now are largely observational, and that large randomized trials are necessary to assess safety."Neither estrogen nor progesterone are known to be safe for women with a prior diagnosis of breast cancer," she said.

She noted that alternatives to HRT exist for prevention of osteoporosis, such as vitamin D, raloxifene, and diet.Alternatives are also available for the prevention of other diseases such as cardiovascular disease, she said.

For now, she suggested that "it's much better to enter women in studies of these approaches than treat them [with HRT]."

-Westport Newsroom 203 319 2700