In new research presented at the Advanced Breast Cancer Fourth International Consensus Conference (ABC 4), researchers have shown that combining targeted drugs with hormone therapy results in a significant increase in the risk of severe or life threatening adverse events (grades 3 and 4).
However, the researchers, Dr Matteo Lambertini, a medical oncologist at the Institut Jules Bordet (Brussels, Belgium) and Professor Samuel Martel, a medical oncologist at CISSS Montérégie Centre/Hôpital Charles-Lemoyne, Université de Sherbrooke (Québec, Canada), say that most of these side effects are treatable and potentially preventable, and that the information gained from their research will enable doctors and patients to make more informed choices, as well as providing the basis for further research.
Previous studies have shown that patients with advanced breast cancer live longer without their disease progressing if they are treated with combination therapy, but, until now, it was not known to what extent these combined treatments could lead to more and worse adverse side effects.
Breast cancers that are described as "hormone receptor-positive" have receptors that receive signals from hormones such as oestrogen and progesterone that tell the cancer cells to proliferate. Drugs such as tamoxifen, which blocks the oestrogen receptors, interrupt these hormonal messages. Nowadays, in patients with advanced disease, they are often given in combination with other drugs that target specific molecules important for cancer development; for instance, trastuzumab is a monoclonal antibody targeting breast cancers that produce the protein HER2.
In the study presented today, the researchers analysed data from 8,529 patients who had taken part in 16 randomised controlled clinical trials up to July 2017. The patients all had advanced hormone receptor-positive breast cancer that had spread away from the site of the original tumour (metastatic or advanced breast cancer), and the trials investigated hormonal therapies given in combination with targeted drugs, such as CDK4/6, PI3K or mTOR inhibitors, and anti-HER2 agents. The patients had been randomised to receive either the combination therapy or the hormonal therapy alone.