Afinitor impresses in advanced hormone-positive breast cancers

One of the most highly anticipated presentations at this year's SABCS is BOLERO-2 (Breast Cancer Trials of Oral Everolimus-2), a phase 3 study examining whether adding Afinitor (everolimus) to Aromasin (exemestane) in postmenopausal women with advanced estrogen-positive breast cancer would delay disease progression. The study followed 724 patients with progressing breast cancer who have responded to previous hormone therapy for their cancer.The BOLERO-2 trial was halted in February when it became apparent the Afinitor combination was better than Aromasin alone, much sooner than expected, said investigator Gabriel N. Hortobagyi, MD, director of the Breast Cancer Research Program at the University of Texas M.D. Anderson Cancer Center in Houston. Preliminary data were announced at a European meeting in September showing that with the addition of Afinitor, progression-free survival (PFS) improved from 2.8 months to 6.9 months. Researchers announced updated results at the San Antonio Breast Cancer Symposium, and after a year follow-up PFS had improved from 3.2 months in the Aromasin arm to 7.4 months in the Aromasin and Afinitor arm, an improvement of about 57 percent. Response rates also doubled from 25.5 to 50.5 percent, which included complete and partial responses, as well as stable disease lasting at least six months. Side effects in the combination arm included oral mucositis, rash, diarrhea and fatigue.Data also suggest a survival benefit, but researchers were quick to caution that survival results arenot expected for another year. Hortobagyi says it may be another year before survival data is available. Afinitor inhibits mTOR, a protein that helps regulate the growth of cancer cells and blood vessels. Aromasin is a commonly used drug in hormone-positive cancers that inhibits the enzyme aromatase, blocking its conversion to estrogen, the hormone that drives tumor growth in certain breast cancers. It's believed that some cancers that are resistant to hormonal therapy have an over-activation of the mTOR pathway. By using an aromatase inhibitor in combination with Afinitor, researchers hope to overcome that resistance. At last year's symposium, results of a study suggested that women with metastatic disease taking Afinitor and tamoxifen live longer. Two other BOLERO studies are looking at whether Afinitor benefits women when combined with Herceptin (trastuzumab) and Taxol (paclitaxel) or vinorelbine. Afinitor is currently approved to treat advanced kidney cancer. Novartis, the drug's maker, is expected to submit Afinitor to the FDA for use in advanced breast cancer within the next few weeks in light of the positive results. You can read about the study in the New England Journal of Medicine.