Drugmakers Roche (NASDAQOTH:RHHBY) and ImmunoGen (NASDAQ:IMGN) are the latest companies to reveal promising clinical data at this year's European Society for Medical Oncology Congress. The exciting news today stems from positive phase 3 clinical trial data related to their developmental cancer therapeutic, trastuzumab emtansine.

Trastuzumab emtansine, or T-DM1 for short, is made up of three distinct components: Trastuzumab is an antibody that specifically targets a protein involved in cancer cell growth, emtansine is a molecule that kills cancer cells, and the two parts are molecularly bound together through a linker.

If you forgive the violent imagery, you can think of this drug kind of like a paratrooper. The antibody is a parachute -- or targeted delivery system -- the linker is the brave soldier, and the molecule that causes cell death is the rifle. Roche already owns the intellectual property for trastuzumab through its subsidiary Genentech, but has licensed both emtansine and the linker from ImmunoGen.

The drug was tested in patients suffering from HER2-positive breast cancer who have already received prior treatment, while another group of patients with the same diagnosis received the commonly prescribed drug combination lapatinib, which is sold under the brand name Tykerb by GlaxoSmithKline (NYSE:GSK), and capecitabine, which is marketed as Xeloda by Roche. T-DM1 drastically improved patients' survival rates by a median of 5.8 months, and the overall risk of death dropped by 32% compared to the group treated with the lapatinib/capecitabine combination. This latest data reinforces the positive clinical study results that Roche and ImmunoGen reported this summer.

Patients aren't the only ones happy with these results. Shares of both Roche and ImmunoGen popped by about 2% on the news. Roche, which is carrying the development of the drug forward through its Genentech group, recently filed a Biologics License Application with the Food and Drug Administration in order to get the drug approved. Investors should continue to watch this news closely until the drug gets the official OK from the U.S. regulatory agency to be commercialized.

Max Macaluso, Ph.D. has no positions in the stocks mentioned above. The Motley Fool owns shares of GlaxoSmithKline. Motley Fool newsletter services recommend GlaxoSmithKline and ImmunoGen. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.