The present application describes the use of low HER3 as a selection criterion for treating patients with a HER inhibitor, such as pertuzumab. It also describes the use of high HER2:HER3 ratio as a selection criterion for treating cancer patients, such as ovarian cancer patients, with a HER inhibitor, such as pertuzumab. In addition, the application describes the use of high HER3 as a selection criterion for treating cancer patients with a chemotherapeutic agent, for instance gemcitabine.
