At the annual American Society of Clinical Oncology (ASCO) conference this week, Genentech released results of a phase III clinical trial of T-DM1. The data showed improvement in progression-free survival of just over 3 months in women with Her2 positive metastatic breast cancer. T-DM1 is a drug BCAction has been following for some time. This drug enables targeted delivery of chemo to HER2+ cancer cells. Based on recent results, Genentech has said they will seek FDA approval.
We do not believe progression free survival is an adequate substitute for overall survival. The T-DM1 data on overall survival is not yet mature, and while there appears to be a benefit, it is too early to know if it is statistically significant. In evaluating new drugs and their benefit to women, we also consider cost (unknown at this time) and side effects. While there are still a large number of women experiencing severe side effects (grade 3 or worse) the percentage is smaller than with standard chemo (41% compared to 57% on standard chemo). At this point, we are continuing to monitor and evaluate the data. The importance of days and weeks and months for women who are dying cannot be underestimated. However, we’re still talking about incremental progress and let’s be clear – we need better.
The real significance of this ‘breakthrough’ – if it is that – is in the science of attaching a cytotoxic agent in this case Maytansine, to the monoclonal antibody Trastuzumab (Herceptin) using a stable linker. Though Genentech’s process for creating the conjugate is proprietary, the potential is there for other conjugates to be found using that process or newly discovered processes and with different drugs and antibodies, which might work better and for different subtypes.
Of course, it’s hard to get really excited. The media and medical uproar inspired by this additional 3.2 months of progression free survival is a sobering reminder of how desperately we need improved options for women with metastatic disease.