Posted on behalf of Alla Katsnelson

Hopes for breast-cancer treatment were buoyed today by clinical trial results reporting that two experimental medicines delay the worsening of tumours by several months in women with advanced forms of the disease.

One of the two therapies, a monoclonal antibody called pertuzumab and developed by Genentech (owned by Roche), targets the HER2 protein, the same pathway targeted by the widely used breast-cancer drug trastuzumab (Herceptin). (Mutations in the HER2 gene drive about 20–30% of breast cancer cases by causing elevated levels of the protein.) In the trial, published in the New England Journal of Medicine and reported on 8 December at the San Antonio Breast Cancer Symposium in Texas, women with metastatic breast cancer given both pertuzumab and trastuzumab, along with a chemotherapy drug, showed a median 6.1-month lull in the progression of their disease.

The results give a boost to efforts to design cancer therapies by targeting mutations in a specific tumour gene. As Nature reported in September, researchers achieved similarly promising results with an experimental treatment for melanoma, targeting a mutated version of the protein B-RAF. In addition to trastuzumab, two other genetically targeted cancer therapies, imatinib (Gleevac) and erlotinib (Tarceva), have been approved.

The second medicine, an already-approved pill called everolimus (Afinitor) developed by Novartis, works by depleting oestrogen by inhibiting a protein called mTOR. In a study of 724 post-menopausal women with hormone-dependent breast cancer, women who took the drug combined with a hormone therapy medicine called exemestane went a median of 4.2 months longer without a worsening of their tumours than women who took the hormone therapy alone. The findings were also presented at the San Antonio meeting. (Earlier data on everolimus was also published today in the New England Journal of Medicine.)

It’s not yet clear whether the two drugs prolong the lives of women taking them, although data from the studies hint that they may. Bevacizumab (Avastin), another monoclonal antibody developed by Genentech, showed a similar level of improvement as pertuzumab, but did not extend survival. Last month the US Food and Drug Administration withdrew its approval of Avastin for treating women with advanced breast cancer.

CORRECTION: An earlier version of this blog post incorrectly identified the product name of iminitib with erlotinib and vice versa.