Abstract #3142 Background: Most HER2+ metastatic breast cancer (MBC) patients who initially respond to trastuzumab (T)-based therapies will experience disease progression (PD). Standard practice is to discontinue the cytotoxic agent on which disease progressed, however there is evidence that tumors may remain sensitive to HER2 targeting and that there may be a potentiating effect of T on chemotherapy. We examined the treatment history of a large population of HER2+ MBC patients to assess outcomes associated with continuation of T beyond PD.
Methods: This analysis was carried out on patients enrolled in registHER, a prospective observational study of 1023 patients with newly diagnosed (within 6 months) HER2+ MBC. Median f/u from MBC diagnosis is 25 months at the time of data cut-off (12/31/07). For those treated with T prior to first PD, we compared demographics and baseline tumor characteristics for those patients treated with or without T following first PD. Treatment with T was defined as a minimum of 21 days of therapy prior to PD. In addition, we evaluated time to second PD, and overall survival post PD (both endpoints calculated from initial PD). Overall survival (OS) was also calculated from the date of treatment initiation to death for the entire treated cohort.
Results: Of 1023 evaluable patients, 873 (85%) were treated with any T-based first-line therapy. 622 T-treated patients progressed and 500 were subsequently treated with T following first PD. Patients who received T post first PD tended to be younger ( Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3142.