Genentech, the South San Francisco-based unit of Roche, said it has turned in its application to the FDA to start selling a souped-up version of the hit breast cancer drug trastuzumab (Herceptin). The new antibody is attached to a toxin to give it more tumor-killing punch. The drug, known as T-DM1, was developed by Genentech with technology from Waltham, MA-based ImmunoGen (NASDAQ: IMGN). Last December, Genentech showed in a clinical trial it was able to completely or partially shrink tumors for about one-third of women who had received an average of seven prior rounds of treatment. I wrote an in-depth feature last month about the twists and turns of T-DM1’s development history.