Two studies have established that inexpensive generic drugs currently used to treat different conditions hold the potential of reducing breast cancer deaths across the globe.
The studies, published in the The Lancet, suggest that two different classes of drugs, aromatase inhibitors (AIs) and bisphosphonates, have the potential of improving survival prospects for postmenopausal women with early breast cancer. Further, researchers have also suggested that the two types of drug can be used together, which could even increase the benefits while reducing some side-effects.
Surgeries are effective against breast cancer, but even though it can remove all detectable disease, there are cases when dangerous undetected micrometastases (small secondary tumours) are left behind. These secondary tumours could later lead to breast cancer recurrence if left untreated.
Previous studies have established that about 80% of breast cancers are hormone sensitive (ER-positive), which means that they can be stimulated by the body’s own hormones, such as oestrogen. Endocrine treatments, which act to stop hormones stimulating cancer cells, can help protect against breast cancer recurrence.
The two reports published in The Lancet provide the best evidence yet for the effects of AIs and bisphosphonates on postmenopausal women with early breast cancer.
In the first study, which brought together evidence from 30,000 postmenopausal women in 9 randomised trials, it was found that women who received 5 years of treatment with the newer endocrine therapy (ie, an AI) had a better survival than five years of standard endocrine therapy (tamoxifen). Women on AI for five years reduced the likelihood of the cancer recurring by about a third (30 per cent), and the risk of dying from breast cancer by around 15 per cent throughout the decade after beginning treatment. The researchers estimate that, compared to no endocrine treatment, the risk of dying from breast cancer for women who took AIs would be reduced by around 40 per cent in the decade after beginning treatment.
The second study is based on evidence from another 20,000 women in 26 randomised trials, showing that 2-5 years of treatment with a class of drugs called bisphosphonates, which are usually used to treat osteoporosis, reduces the risk of breast cancer recurring in post-menopausal women, and also significantly extends survival. However, bisphosphonate treatment appears to have little effect in premenopausal women.
The most common site for breast cancers to spread to is bone. Tumour cells released from the primary breast cancer can remain dormant in the bone for years before spreading to other parts of the body. Bisphosphonates alter the bone microenvironment, which could make it less favourable for cancer cells and so reduce the risk of cancer recurrence in the bone and in other organs. Taken separately, previous clinical trials of bisphosphonates in early breast cancer have shown mixed results, but taking all their results together, a clearer picture emerges.
The meta-analysis included individual patient data on 18 766 women in 26 randomised trials, comparing between two and five years of bisphosphonates versus no bisphosphonate. In the overall study population, the only clear benefit of bisphosphonates was a 17 per cent reduction in recurrence of cancer in the bone. However, among postmenopausal women, bisphosphonate treatment produced a larger reduction in bone recurrence of 28 per cent and also reduced the risk of dying from breast cancer by 18 per cent during the first decade after diagnosis.
This benefit appeared to be irrespective of the type of bisphosphonate, treatment duration, how big the tumour was, whether it had spread to the lymph nodes, or whether or not it was oestrogen-receptor (ER) positive. However, bisphosphonate treatment did not reduce the risk of new breast cancers developing in the opposite breast.
