"A combination of two drugs delays progression of advanced aggressive breast cancer by an average of nine months  working in all subsets of the most common type of breast cancer. The combination  of a firstinclass targeted drug called palbociclib and the hormone drug fulvestrant  slowed cancer growth in around two thirds of women with advanced forms of the most common type of breast cancer. The combination allowed many women with metastatic hormonereceptorpositive HERnegative cancer to delay the start of chemotherapy which is the traditional treatment option in these patients once hormone drugs have stopped working.  The international study led in the UK by Dr Nicholas Turner from The Institute of Cancer Research London and The Royal Marsden NHS Foundation Trust updates the results of a major phase III trial published last year.  The results confirm the prior benefit observed with palbociclib and show that palbociclib works regardless of how sensitive patients cancer was to earlier hormone therapy. The new research published today Thursday in The Lancet Oncology shows that even women with specific genetic changes conveying resistance to hormone therapy can benefit from the new drug combination. Hormonereceptorpositive HERnegative cancer accounts for around  per cent of cases of breast cancer. In the trial researchers from  research centres in  countries followed  women allocated to receive either palbociclib and fulvestrant or a dummy pill and fulvestrant. The trial was funded by Pfizer. Women in the palbociclib plus fulvestrant group took a median of . months to progress as measured by CT and MRI scans compared with . months in the placebo group. Some  per cent of the  women in the palbociclib plus fulvestrant group showed clinical benefit  either a reduction in tumour size or control of disease for at least six months  compared with  per cent of the  women in the placebo plus fulvestrant group. Some  per cent in the palbociclib plus fulvestrant group had a decrease in tumour size compared with  per cent in the placebo plus fulvestrant group.  The study also aimed to assess whether cancers with particular genetic traits responded less well or better to the combination than others. Mutations to the gene PIKCA represent the most common genetic event in breast cancer and mutations in the gene are associated with a shorter response to hormone therapy. The research showed that using liquid biopsies that measure cancer DNA circulating in the blood to detect PIKCA and tests for blood hormone levels the palbociclib combination worked in all types of hormonereceptor positive HER negative breast cancer. Palbociclib is a firstinclass drug  with a different mechanism of action to other approved drugs  which simultaneously blocks two proteins called CDK and CDK in cancer cells. It causes less severe sideeffects than traditional chemotherapy. In the trial severe sideeffects caused by the combination were rare. Many women  per cent on the palbociclib arm had a drop in their white blood cell count but this rarely led to serious symptoms. Study colead author Dr Nicolas Turner Team Leader in Molecular Oncology at The Institute of Cancer Research London and Consultant Medical Oncologist at The Royal Marsden NHS Foundation Trust said Our research underlines the effectiveness of palbociclib with fulvestrant in metastatic breast cancer and importantly demonstrates its benefit in all types of hormonereceptor positive breast cancer. We hope our results lead to the adoption of this drug combination in breast cancer where it delays the need to start chemotherapy by an average of nine months. Our study also sends a powerful message that in combining new drugs in innovative trials we can find better options for women with advanced breast cancer. Chemotherapy can add several months to life but it comes at a cost of often lifelimiting side effects and we need alternative treatments that are better tolerated to treat patients with advanced breast cancer.  Professor Paul Workman Chief Executive of The Institute of Cancer Research London said If were going to drive further improvements in survival from cancer its essential that we find ways of prolonging life in people whose cancers have evolved and become resistant to treatment. This trial is an exciting example of one of the most promising approaches to overcoming drug resistance by combining drugs with different mechanisms of action to block off cancers escape routes. Its very encouraging to see such substantial delays to cancer progression. Notes to editors For more information please contact Henry French on    or henry.frenchicr.ac.uk mailtohenry.frenchicr.ac.uk. For enquiries out of hours please call   . The Institute of Cancer Research London is one of the worlds most influential cancer research institutes. Scientists and clinicians at The Institute of Cancer Research ICR are working every day to make a real impact on cancer patients lives. Through its unique partnership with The Royal Marsden NHS Foundation Trust and benchtobedside approach the ICR is able to create and deliver results in a way that other institutions cannot. Together the two organisations are rated in the top four cancer centres globally. The ICR has an outstanding record of achievement dating back more than  years. It provided the first convincing evidence that DNA damage is the basic cause of cancer laying the foundation for the now universally accepted idea that cancer is a genetic disease. Today it leads the world at isolating cancerrelated genes and discovering new targeted drugs for personalised cancer treatment. As a college of the University of London the ICR provides postgraduate higher education of international distinction. It has charitable status and relies on support from partner organisations charities and the general public.  The ICRs mission is to make the discoveries that defeat cancer. For more information visit http"