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.
The purpose of this study is to determine if margetuximab is effective in the treatment of certain patients with relapsed or refractory advanced breast cancer.