Two inexpensive classes of drugs available in generic form each reduce the recurrence of breast cancer in post-menopausal women as well as death rates from the disease, a pair of studies reported.
Taking the medications together may further boost anti-cancer benefits and help cancel out undesirable side-effects of one of the drugs, according to the research published in medical journal The Lancet.
The first "meta-study" pulling together data from nine trials covering 30,000 post-menopausal women found endocrine treatments based on a class of drugs called aromatase inhibitors yield higher survival rates after five years compared to standard endocrine therapy with tamoxifen.
The likelihood of cancer recurring was cut by about a third and the risk of dying by about 15 percent in the decade after treatment started. Compared to no treatment at all, the danger of dying from breast cancer fell by 40 percent, the study found.
Most women have already passed through menopause when breast cancer strikes. Even after surgery has removed all detectable traces, tiny amounts of the body's own hormones can cause cancer cells to grow.
Endocrine therapies are designed to impede these hormones from stimulating the disease, and so help protect against relapse.
"But aromatase inhibitor treatment is not free of side-effects and it's important to ensure that women" who suffer them are "supported", said the study's lead author, Mitch Dowsett of The Institute of Cancer Research in London.
The second meta-study, which scanned the results of 26 trials involving another 20,000 women, showed that another class of drugs called bisphosphonates –- usually taken to treat osteoporosis, a bone-weakening condition that becomes more common with age –- also significantly boosted survival when taken for at least two years.
When breast cancer spreads, bone is its favoured destination. Tumour cells released from the primary breast cancer can remain dormant in bones for years before moving to other parts of the body.
Bisphosphonates make the bones a less hospitable environment for the cancer cells and so reduce the risk of cancer recurring. The beneficial effect were found to be far more pronounced in post-menopausal women, regardless of the treatment duration, the size of the tumour or whether the cancer had spread to lymph nodes.
The therapy did not, however, reduce the risk of new cancers developing in the opposite breast.
"These simple, well-tolerated treatments should now be considered for routine use" in women with natural or medically induced menopause, lead author Robert Coleman from the University of Sheffield said in a statement.
Some two-thirds of all women with breast cancer are post-menopausal with hormone-sensitive tumours, so could potentially benefit from both drugs, the researchers conclude.
"The drugs are complementary," noted Oxford University's Richard Gray, lead statistician for the studies. "The main side effect of aromatase inhibitors is an increase in bone loss and fractures, while bisphosphonates reduce bone loss."