Pertuzumab monotherapy following trastuzumab-based treatment
 

http://www.abstract.asco.org/AbstView_65_34193.html

Hopeful

"The combination of the two antibodies appears to be more active than either antibody alone. The combination is also active in patients that had failed both antibodies given separately. In clinical studies, the use of the two antibodies combined is justified."

It's like the combination amounts to an entirely new drug.