Review of the contemporary cytotoxic and biologic combinations available for the treatment of metastatic breast cancer.

Background: Treatment of metastatic breast cancer (MBC) with > or =2 chemotherapeutic agents concurrently has been shown to increase response rates, often at the cost of a substantial increase in toxicity, and with minimal impact on the overall survival. However, some combinations of the newer cytotoxic agents, as well as combinations of chemotherapeutic agents and targeted biologic anticancer agents, can produce synergistic efficacy with a manageable toxicity profile.

Objectives: The aims of this work were to provide an overview of the currently approved combination regimens available for the treatment of MBC and to consider the clinical data supporting other drug combinations that may supplement the current therapeutic choices in the near future.

Methods: Literature searches were performed using MEDLINE/PubMed, with a focus on combination therapies for the treatment of MBC that are approved by the US Food and Drug Administration (FDA) or in Phase III clinical trials. The National Institutes of Health's Clinical Trial Registry was searched for relevant ongoing clinical trials in specific areas. Bibliographies were also searched for additional relevant material. Preference was given to recently published, larger, well-designed clinical trials that influence current prescribing practices. Phase I and II studies, and/or studies older than 10 years (ie, published earlier than 1999), were afforded less emphasis or were disregarded.

Results: Combinations of taxanes with capecitabine or gemcitabine, and ixabepilone plus capecitabine, are approved by the FDA as combination regimens for the treatment of MBC. The use of targeted therapies such as trastuzumab, bevacizumab, or lapatinib in combination with taxanes (for the former two) or capecitabine (for lapatinib) is also approved. Several investigational drug combinations are also currently undergoing evaluation in clinical trials, including combinations of bevacizumab and gemcitabine with capecitabine or alternative taxanes. Although results from Phase I and II studies are largely encouraging so far, the data from ongoing Phase III studies will ultimately dictate changes in clinical practice. It seems unlikely that any single agent or combination regimen will emerge as superior in all patients with MBC, given the heterogeneous nature of the disease and patient population.

Conclusion: New combination regimens for MBC may broaden the range of treatment options currently available to delay disease progression for as long as possible.