<qa>  What is the name of the drug that blocks proteins that make cancer cells grow?The purpose of this study is to determine if the addition of tipifarnib to standard letrozole therapy leads to a better response to treatment for your cancer in comparison to letrozole plus a placebo. Tipifarnib belongs to a class of drugs called Farnesyl Transferase Inhibitors FTI. It blocks proteins that make cancer cells grow. 