Phase 2 Study of the Monoclonal Antibody MGAH22 (Margetuximab) in Patients With Relapsed or Refractory Advanced Breast Cancer

In the pivotal study that established that Herceptin® was highly effective when added to standard chemotherapy in the front-line treatment of women with HER2 positive metastatic breast cancer, benefit appeared to accrue to those patients whose tumors expressed the HER2 oncoprotein at the 3+ level by immunohistochemistry (IHC) or those patients whose tumors demonstrated evidence of HER2 gene amplification by fluorescence in situ hybridization (FISH) testing. Similarly, when Herceptin® was used as a single therapy in women with metastatic breast cancer that had progressed following cytotoxic chemotherapy, 3+ overexpression of HER2, but not 2+ expression, was associated with response to treatment. These and other studies have led to the recommendation that Herceptin® should be administered to patients with breast cancer whose tumors exhibit 3+ overexpression or gene amplification. This study will evaluate whether treatment of patients with tumors that would not be expected to respond to Herceptin® therapy, namely those that lack HER2 gene amplification and express the oncoprotein at the 2+ level by IHC, may benefit from the use of the anti-HER2 monoclonal antibody, MGAH22. If 5 or more responses are seen in 41 evaluable patients, then further clinical development of margetuximab will be justified.