Washington, Aug 11 : A risk-benefit analysis is absolutely essential before women begin hormone therapy given its link to breast cancer, says a new study.

The California Teachers study analysed hormone replacement therapy used among 2,857 women for almost 10 years.

"The benefits of hormone therapy for relief of postmenopausal symptoms among women are clear, but the risks are more complicated than we had previously thought," said Tanmai Saxena of the University of Southern California.

Saxena and colleagues found that women who used estrogen therapy for more than 15 years had a 19 percent greater risk of developing breast cancer than women who had never used hormone therapy.

And those who used combined therapy with estrogen plus progestin for 15 or more years had an 83 percent greater risk.

Breast cancer risk was highest among women who used the combination regimen.

Breast cancer risk seemed dependent on body mass index (BMI). Those with a BMI less than 30 appeared to have an increased risk of breast cancer with combined hormone therapy; the risk was strongest among women with BMI less than 25.

In contrast, obese women (i.e., BMI of 30 or more) had no further increase in risk associated with using combined hormone therapy.

Finally, the risk of breast cancer was confined to tumors that were positive for both estrogen and progestin receptors.

"These results add new evidence that risk does vary by other personal characteristics. However, for now, the public health message remains essentially the same," said Susan Hankinson of Harvard Medical School.

"There is an increased risk of breast cancer from hormone use, and further studies will address the question of how specific that risk is," she added.

The findings were published in Cancer Epidemiology, Biomarkers & Prevention. (ANI)