T-DM1 is an experimental targeted therapy medicine that's a combination of Herceptin (chemical name: trastuzumab) and a chemotherapy medicine called maytansine. Researchers are studying T-DM1 to see if it would be a good treatment for HER2-positive, advanced-stage breast cancer that has stopped responding to other treatments.
Cancer medicines are usually considered for FDA approval when the results of a large study (called a phase III clinical trial) are available. Still, some cancer medicines are considered for "accelerated approval" based on the results of one or more smaller studies. Accelerated approval usually is considered when results from one or more smaller, phase II clinical trials suggest that the new medicine may be a good option for people who haven't responded or stopped responding to other available treatments already approved by the FDA.
The U.S. Food and Drug Administration (FDA) decided to not consider accelerated approval for T-DM1 to treat HER2-positive, advanced-stage breast cancer based on phase II clinical trial results available as of August 2010. Still, researchers will continue to study T-DM1 and the medicine may be considered for approval in the future, possibly in 2012 when phase III study results are expected to be available.