Two classes of widely available generic drugs, when used together, are more effective than tamoxifen in ensuring breast cancer doesn’t come back after surgery, two related studies concluded.

Two inexpensive, generic drugs can reduce breast cancer deaths in postmenopausal women better than drugs now in wide use, researchers from two related studies concluded.

Drugs called aromatase inhibitors help stop hormones including estrogen from spurring cancer growth. These drugs are more effective than widely used tamoxifen in reducing breast cancer death, according to the research.

A second drug class called bisphosphonates makes it more difficult for cancer tumors to develop in bones, which can be a side effect of aromatase inhibitors.

Researchers said taking the two drugs together during the early stages following breast cancer surgery reduces the risk of death even further.

“The drugs are complementary because the main side effect of aromatase inhibitors is an increase in bone loss and fractures while bisphosphonates reduce bone loss and fractures as well as improving survival,” Oxford professor Richard Gray, Ph.D., the lead statistician for both studies, said in a press statement.

The findings of both studies appeared today in the British medical journal The Lancet.

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The first study analyzed evidence from 30,000 postmenopausal women in nine different drug trials. Most breast cancers occur after menopause.

Using newer endocrine therapy, such as aromatase inhibitors, for five years led to better survival rates than using five years of standard endocrine therapy, including tamoxifen.

Aromatase inhibitors reduced the likelihood of breast cancer recurring by 30 percent when compared to tamoxifen, which most U.S. breast cancer patients take for five to 10 years after they finish chemotherapy. Aromatase inhibitors reduced the risk of death by 15 percent in the decade after diagnosis.

Patients who received aromatase inhibitors had a 40 percent less chance of dying from breast cancer than postmenopausal women who received no endocrine treatment.

The inhibitors work by removing hormones like estrogen from the circulation systems of postmenopausal women. Breast cancer cells use hormones to fuel their growth in four out of five cases.

“The impact of aromatase inhibitors is particularly remarkable given how specific these drugs are,” said professor Mitch Dowsett, Ph.D., of The Institute of Cancer Research in London.

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The second study involved evidence from another 20,000 women in 26 clinical trials.

Researchers found that using bisphosphonates for two to five years increases the survival rate for postmenopausal women with breast cancer, although they seem to have little effect on premenopausal women.

Bones are the most common sites for breast cancer to spread. Aromatase inhibitors taken by themselves make such a metastasis even more likely.

Bisphosphonates, commonly used to treat osteoporosis, make bones a less hospitable place for breast cancer tumors.

Postmenopausal women who took bisphosphonates reduced their risk of seeing their cancer reemerge in their bones by more than a quarter, the study found. They cut their risk of dying from breast cancer by nearly a fifth.

“These simple, well tolerated treatments should now be considered for routine use in the treatment of early breast cancer in women with either a natural or medically induced menopause to both extend survival and reduce the adverse effects of cancer treatments,” said Dr. Robert Coleman, a professor at the University of Sheffield in the United Kingdom and lead author of the bisphosphonates study.

“These studies provide really good evidence that both of these inexpensive, generic drugs can help to reduce breast cancer mortality in postmenopausal women,” Gray said.

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