Wednesday, June 11, 2008

Are Her2 inhibitors an alternative to chemo in breast cancer?

Herceptin Fab (antibody) - light and heavy chainsImage via WikipediaSeveral studies exploring the use of lapatinib (Tykerb, GlaxoSmithKline) in metastatic breast cancer have suggested that it may offer an alternative to chemotherapy in this setting, both as monotherapy, and in combination with other targeted therapies.

One study explored the use of lapatinib alone, whereas others investigated combinations with trastuzumab (Herceptin, Genentech/Roche), with bevacizumab (Avastin, Genentech/Roche), and with the investigational agent pazopanib (under development by GlaxoSmithKline).

Studies presented at American Society of Clinical Oncology opened up an interesting debate regarding whether biological therapy without chemotherapy for metastatic breast cancer is feasible.

The efficacy of these targeted agents is higher when they are combined with chemotherapy, and the toxicity of these agents in combination needs to be explored further. Hence, the preferred front-line choice for metastatic breast cancer is presently trastuzumab with chemotherapy, and the evidence suggests that continuation of trastuzumab is the best option for patients who progress. Combining drugs that have different targets is also a promising option.

Lapatinib is currently approved in the US for a very narrow indication in combination with capecitabine (Xeloda, Roche) for advanced metastatic HER2+ breast cancer in women who have received previous chemotherapy, including an anthracycline, a taxane, and trastuzumab. A similar approval in Europe is pending with the EMEA.

The largest of the new trials presented was a phase 3 study of lapatinib monotherapy compared with a combination of lapatinib and trastuzumab (EGF104900). Both of these drugs target HER2+ breast cancer, but trastuzumab (a monoclonal antibody) is a large-protein molecule that targets the part of the HER2 protein on the outside of the cell; lapatinib (an oral drug) is a smaller molecule that enters the cell and blocks the function of this and other proteins intracellularly. The combination effectively attacks HER2 from multiple angles.

The trial involved 269 patients with HER2+ breast cancer who had documented progression on trastuzumab in the metastatic setting. The combination of lapatinib plus trastuzumab showed a significant increase in progression-free survival, compared with lapatinib alone (12 weeks vs 8.1 weeks). This translates into a 27% reduction in the risk for disease progression (hazard ratio [HR], 0.73; P = .008). The overall clinical-benefit rate (the response rate and the rate of durable stable disease) for the combination was double that for monotherapy (24.7% vs 12.4%; P = .01). There was a trend toward improved overall survival.

More data on the role of combined HER2+ therapy in combination with chemotherapy will be available soon from the ongoing ALTTO (Adjuvant Lapatinib and/or Trastuzumab Treatment Optimization) study. ALTTO is being conducted in less-heavily pretreated patients with early-stage disease.

A trial of lapatinib plus bevacizumab was reported in a small phase 2 single-group study, conducted in 32 patients who had received a median of 5 previous metastatic breast cancer therapies. 28 of these 32 patients had received prior treatment with trastuzumab.

The combination resulted in a 34.4% clinical-benefit rate (defined as complete response plus partial response plus stable disease at 24 weeks or more), and 62.5% of patients were progression free at week 12.

The most common adverse events were diarrhea (81%), rash (66%), nausea (56%), fatigue (56%), and vomiting (46%). There were 2 grade 2 asymptomatic LVEF decreases, 1 grade 3 gastrointestinal hemorrhage, and 1 grade 3 hypertensive event.

Overall, blocking both the HER2 and the VEGF pathways led to anticancer activity for even heavily pretreated patients with metastatic breast cancer that could potentially advance the treatment of this high-risk disease.

A combination study of lapatinib plus pazopanib, where both drugs were taken orally once daily, suggested that they might provide a potential future treatment option for HER2+ breast cancer. It involved 141 patients and compared the combination with lapatinib monotherapy.

The results confirmed the efficacy of lapatinib monotherapy and showed a trend toward better outcomes with the combination. At 12 weeks, 36.2% of patients taking the combination and 38.9% taking the monotherapy experienced disease progression (P=.37). The response rate was 44.9% with the combination and 28.8% with the monotherapy according to investigator assessment, and 36.2% vs 22.2%, respectively, according to independent assessment.

1 comment:

Dominus said...

The combination of trastuzumab and lapatinib certainly looks very promising.