An experimental drug could keep melanomas and breast cancer from resisting targeted therapies, according to findings reported at the 2013 International Conference on Molecular Targets and Cancer Therapeutics. Called LEE011, the new drug inhibits proteins called cyclin-dependent kinases (CDKs), which make cells divide. The targeted CDKs are abnormally active in many cancers, including melanomas with BRAF mutations and breast cancers with PIK3CA mutations. The researchers found that LEE011 keeps cultured tumor cells from dividing and that combining the drug with targeted treatments prevents resistance in melanomas and breast cancer in mice. Now, these combination treatments are being tested in several phase I clinical trials on a variety of cancers in adults, as well as in children.