According to a combined analysis of five clinical trials, treatment of metastatic colorectal cancer, breast cancer, or non–small lung cancer with a combination of Avastin and chemotherapy results in a higher risk of arterial blood clots than treatment with chemotherapy alone. These results were published in the Journal of the National Cancer Institute.

Avastin is a drug that blocks a protein known as vascular endothelial growth factor (VEGF). VEGF stimulates the growth of new blood vessels.

Drugs that interfere with VEGF can slow or stop the growth of cancer cells. In addition, drugs that interfere with VEGF may improve the delivery of chemotherapy to cancer cells by normalizing blood supply.

While clinical trials have indicated that the combination of Avastin and chemotherapy improves survival among patients with certain types of metastatic cancer, some of these trials have also suggested that this treatment combination may increase the risk of blood clots in the arteries.

To provide additional information about the risk of blood clots in patients treated with Avastin and chemotherapy, researchers combined information from five clinical trials. These trials enrolled a total of 1,745 patients with metastatic colorectal, breast, or non–small cell lung cancer. Each of the trials compared the combination of Avastin and chemotherapy to chemotherapy alone.

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Patients were classified as having an arterial blood clot if they experienced one of the following adverse events: angina pectoris, arterial thrombosis, cerebral infarct, cerebral ischemia, cerebrovascular accident, myocardial infarction, or myocardial ischemia.

  • Risk of a blood clot in the artery was 3.1 per 100 people per year among patients treated with chemotherapy alone and increased to 5.5 per 100 people per year among patients treated with Avastin and chemotherapy.
  • Other factors that increased the risk of arterial blood clots were older age (age 65 or older) and history of arterial blood clots.
  • Risk of a blood clot in a vein was not increased among patients treated with Avastin and chemotherapy.

The researchers conclude that compared to chemotherapy alone, the combination of chemotherapy and Avastin increases the risk of blood clots in the arteries.

Reference: Scappaticci FA, Skillings JR, Holden SN et al. Arterial thromboembolic events in patients with metastatic carcinoma treated with chemotherapy and bevacizumab. Journal of the National Cancer Institute. 2007;99:1232-9.

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