Purpose: To determine the activity of successive trastuzumab-containing regimens in HER2-overexpressing metastatic breast cancer (MBC) as well as the response rate (RR), time to progression (TTP), and predictive factors for response.
Patients and methods: We performed a descriptive retrospective study of trastuzumab activity in patients with HER2-overexpressing MBC treated at our hospital from October 1999 to October 2003.
Results: Fifty-eight patients were evaluated, in whom an overall RR (complete response plus partial response) of 39.7% was obtained for first-time administration of trastuzumab; stable disease (SD) was seen in 29.3%, and the clinical benefit rate was 69%. Median TTP was 6 months (range, 1 months to > 39 months). A total of 31 patients (53.4%) received a second trastuzumab-containing regimen, with an RR of 25.8%; SD was seen in 12.9%, and the clinical benefit rate was 38.7%. Median TTP was 3 months (range, 1 months to > 22 months). A total of 8 patients (14.3%) received a third trastuzumab-containing regimen. The RR for the third trastuzumab regimen was 12.5%; SD was seen in 12.5%, and the clinical benefit rate was 25%. Median TTP was 2 months (range, 1 months to > 12 months). A total of 4 patients (7.1%) received a fourth trastuzumab-containing regimen, with an RR of zero and SD in 25%. Predictive factors for response were disease in soft tissue or bone (P = 0.03; odds ratio [OR], 3.25; 95% confidence interval [CI], 1.08-9.8) and metastases at < 2 sites (P = 0.03; OR, 6.2; 95% CI, 1.25-30.9). We observed a better RR in the second trastuzumab-containing regimen when the patient responded to the first regimen (P = 0.03; OR, 13.2; 95% CI, 1.36-126).
Conclusion: Trastuzumab-containing regimens beyond disease progression in MBC show activity even in heavily pretreated patients. The activity noted does not allow us to ascertain the independent contribution of trastuzumab in this setting. There were more responses in patients with few metastases in the soft tissues or bone. Patients who have shown a previous response to trastuzumab can show a response to a second trastuzumab-containing regimen.