Pemetrexed: A promising new treatment for breast cancer

Metastatic breast cancer is a chemotherapy-responsive disease, and significant palliation of cancer-related symptoms can be achieved with effective treatment. New treatments are needed because patients with metastatic breast cancer commonly outlive the effectiveness of currently available cytotoxic and hormonal treatments. Pemetrexed is a novel antimetabolite that inhibits three enzymes critical in purine and pyrimidine biosynthetic pathways: thymidylate synthase, dihydro-folate reductase, and glycinamide ribonucleotide formyltransferase. Several phase II studies of pemetrexed have showed objective response rates of more than 30% in minimally pretreated metastatic breast cancer patients and approximately 20% in more heavily pretreated patients. Pemetrexed is associated with limited toxicity when administered with folic acid and vitamin B₁₂ supplementation and is therefore a promising agent both for palliative treatment of metastatic disease and for incorporation into combination regimens for treating newly diagnosed metastatic and early-stage breast cancer.