Last Updated: 2003-06-03 16:46:54 -0400 (Reuters Health)

NEW YORK (Reuters Health) - It may be possible to give women a lower dose of the breast cancer drug tamoxifen without dampening its effectiveness, according to a pilot study released Tuesday.

Low doses of tamoxifen had the same impact on an important marker of breast cancer spread as did higher doses, according to the study published in the Journal of the National Cancer Institute.

However, experts say it's far too early to conclude that lower-dose tamoxifen would be as effective as standard doses of the drug.

Tamoxifen acts like estrogen in some parts of the body and like an anti-estrogen in others. It has been shown to decrease the risk of death in women who have estrogen-responsive breast cancer -- meaning estrogen helps fuel the cancer's growth -- and can also help prevent the disease in high-risk women.

Doctors are interested in lower doses of tamoxifen because the drug has been linked to an increased risk of uterine cancer and dangerous blood clots.

A researcher unaffiliated with the new study said the results underscore the importance of tailoring drug dose to the individual.

"It shows that the standard dose may not be right for everyone," Dr. Guiseppe DelPriore, a gynecological oncologist at the New York University Medical Center and an associate professor at the NYU School of Medicine, said in an interview with Reuters Health. "What may be good for one woman may be too strong for another."

For the study, researchers led by Dr. Andrea Decensi of the European Institute of Oncology in Milan monitored the effects of various doses of tamoxifen on 120 women with estrogen receptor-positive breast cancer.

All the women were slated to have surgery to remove tumors from their breasts and went through four weeks of tamoxifen treatment before surgery. The patients were randomly assigned to receive either one, five or 20 milligrams (mg) per day of tamoxifen. The current standard dose of tamoxifen is 20 mg.

Before treatment and at the time of surgery, tumor and blood samples were taken to look for several cancer markers and for markers of osteoporosis and heart disease, such as high cholesterol.

An additional group of 63 women used as "controls" received no tamoxifen, but were tested both before and after surgery for levels of cancer markers.

At the end of the study, researchers determined that one important cancer marker, known as Ki-67, showed a similar decrease -- of about 15 percent -- in all the treatment groups, as compared to an increase of 12.8 percent in the group that got no tamoxifen.

Ki-67 is a marker of tumor-cell proliferation.

But when it came to several other tumor markers, the amount of decrease appeared to be dependent on the dose of tamoxifen.

For this reason, DelPriore said more studies need to be done before doctors start using lower doses of tamoxifen to treat patients.

A reduction of Ki-67 across all the tamoxifen-treated groups is good, DelPriore said, but until longer-range trials are done with low doses, researchers won't know if this translates into longer life for breast cancer survivors.