Today, the Food and Drug Administration approved Afinitor (everolimus) in combination with Aromasin (exemestane) to treat postmenopausal women with advanced hormone-receptor positive breast cancer after treatment with either of the aromatase inhibitors Femara (letrozole) or Arimidex (anastrozole). Hormone-positive breast cancers are driven by estrogen. When the estrogen receptor (ER), a protein expressed by tumor cells, and estrogen bind together, they can promote cell division and survival. Afinitor inhibits the mTOR pathway, which can activate the ER when there is no estrogen and provide another way for the tumor to grow.The approval is based on a phase 3 study of 724 patients with metastatic hormone-positive breast cancer who were randomized to receive either Afinitor and Aromasin or Aromasin alone. Patients in the combination arm had a 4.6 month increase median progression-free survival of 7.8 months compared with those on exemestane alone. Response rates, both complete and partial, also doubled from 25.5 to 50.5 percent. Side effects include mouth ulcers, fatigue and diarrhea. Patients 65 and older had a higher rate of serious side effects, and therefore, need to be closely monitored. Afinitor is also being studied in combination with tamoxifen for the treatment in breast cancer and is approved to treat renal cell carcinoma, pancreatic neuroendocrine tumors andastrocytoma (a type of brain tumor).When he presented the results of the phase 3 study in December Gabriel N. Hortobagyi, MD, director of the Breast Cancer Research Program at the M.D. Anderson Cancer Center in Houston, said,"These results establish a new standard of care for this group of patients." For more information, visit afinitor.com.