Panitumumab Targeted Therapy Provides Anticancer Activity
According to results presented at the 42nd annual meeting of the American Society of Clinical Oncology (ASCO), the targeted agent panitumumab provides high anticancer responses in patients with advanced colorectal cancer that has stopped responding to standard therapies.
Colorectal cancer is the second leading cause of cancer-related deaths in the U.S. Metastatic colorectal refers to cancer that has spread from its site of origin to distant sites in the body.
Standard treatment for metastatic colorectal cancer includes chemotherapy with or without targeted therapy. Although patients with metastatic colorectal may experience an anticancer response to initial therapy, cancer will recur in a majority of these patients, leaving unfavorable survival rates. New treatment approaches and anticancer drugs are needed so that outcomes may be improved.
Panitumumab is a new targeted therapy that has been granted “fast-track” status (a designation for promising drugs that facilitates the approval process) and priority review by the FDA for the treatment of colorectal cancer. Results from recent clinical trials were reported at ASCO and confirm panitumumab’s anticancer activity in colon cancer.
Panitumumab is a monoclonal antibody that binds to specific targets on cancer cells. Panitumumab targets the epidermal growth factor receptor (EGFR), a biologic pathway that is involved in the growth and spread of cancer. By targeting EGFR, panitumumab can destroy cancer cells directly while sparing healthy cells from the side effects of treatment.
Interim results from two clinical trials presented at ASCO appeared to confirm the results of a large previous study evaluating panitumumab in colon cancer. Both trials evaluated panitumumab in patients with metastatic colorectal cancer whose disease had progressed despite prior standard chemotherapy. Patients in both trials had been treated with two or three prior chemotherapy regimens.
Panitumumab therapy was reported to be well tolerated and showed notable anticancer activity-43% of patients achieved disease control. The most common side effects associated with panitumumab were fatigue, abdominal pain, nausea, diarrhea, and side effects to the skin.
Previous results from a Phase III trial (the phase of trials prior to FDA review) were recently reported and indicated a significant reduction in cancer progression among patients with metastatic colorectal cancer that had stopped responding to prior chemotherapy.
This trial was a multi-national trial that included 463 patients who were treated with panitumumab plus best supportive care (BSC) or BSC alone. Best supportive care was defined as the best palliative care available (care to relieve symptoms and improve quality of life), but did not include anticancer chemotherapy.
After a median of seven weeks, 75% of patients initially treated with BSC alone “crossed-over” and were treated with panitumumab due to cancer progression on BSC alone.
- Shrinkage of cancer occurred in 8% of patients treated with panitumumab, whereas no patients treated with BSC experienced shrinkage.
- Stabilization of the disease occurred in 28% of patients treated with panitumumab compared with only 10% treated with BSC.
- The median duration of anticancer responses for those treated with panitumumab was 17 weeks.
- After six months approximately four times as many patients treated with panitumumab were alive without cancer progression as those who were treated with BSC.
- After eight months over twice as many patients treated with panitumumab were alive without cancer progression as those treated with BSC.
The researchers conducting these trials concluded that treatment with panitumumab is generally very well tolerated and provides significant anticancer activity against metastatic colorectal cancer. Longer follow-up will help determine the potential survival benefits associated with panitumumab.
 Hecht J, Mitchell E, Baranda J, et al. Panitumumab Antitumor Activity in Patients (PTS) with Metastatic Colorectal Cancer (mCRC) Expression Low (1-9%) or Negative (<1%) Levels of Epidermal Growth Factor Receptor (EGFr). Proceedings from the 42nd annual meeting of the American Society of Clinical Oncology. June 2006. Atlanta, GA. Abstract #3547.
 Amgen. Randomized Phase 3 Trial Shows Panitumumab Significantly Improved Progression-Free Survival and Disease Control in Metastatic Colorectal Cancer Patients. Available at: . Accessed April 2006.
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