Breast Cancer Drug Raises Blood Clot Risk, Should Have 'Black Box' Warning, JAMA Study Says

Main Category: Breast Cancer
Also Included In: Blood / Hematology
Article Date: 20 Nov 2008 - 9:00 PST

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Genentech's cancer drug Avastin -- which FDA approved in February for treatment of advanced breast cancer -- increases a patient's risk of developing blood clots in veins, a condition known as venous thromboembolism, or VTE, according to a study published Wednesday in the Journal of the American Medical Association, HealthDay News/U.S. News and World Report reports. According to HealthDay News/U.S. News and World Report, FDA's approval of Avastin as a treatment for breast cancer was "controversial" because an FDA advisory committee voted 5-4 against recommending the expanded approval. According to the committee, the drug's ability to slow tumor progression did not outweigh the risks of side effects, such as blood clots and cardiovascular problems. Previously known risks associated with Avastin -- which was approved for lung and colon cancer treatment in 2004 -- include clots in the arteries, heart attacks, strokes and bowel perforations (Gardner, HealthDay News/U.S. News and World Report, 11/18). The Wall Street Journal reports that the study likely will not affect physicians' use of the drug but could lead to changes to its label (Gryta, Wall Street Journal, 11/18).

According to the new study, which analyzed 15 earlier studies, 7.3% of breast cancer patients taking Avastin developed VTE. Overall, patients who took Avastin had a 33% increased risk of developing VTE than did patients who did not take the drug, and the risk was higher regardless of whether patients were taking a low or high dose. Avastin is the first treatment to be approved from a family of drugs designed to attack cancers by cutting off their blood supply through inhibiting the action of a protein that promotes the growth of blood vessels, according to HealthDay News/U.S. News and World Report (HealthDay News/U.S. News and World Report, 11/18). It also is among a new generation of "targeted therapies" that have been touted as safer and gentler than traditional chemotherapy, USA Today reports. Study author Shenhong Wu of Stony Brook University said the magnitude of the drug's risk were not known previously because earlier studies were too small to identify clear trends.

According to USA Today, because blood clots are among the leading causes of illness and death among cancer patients, the study's authors advise that Avastin should receive a "black box" warning from FDA, the agency's strongest warning. Kristina Becker, a spokesperson for Genentech, said Avastin's label already includes a warning about the risk of blood clots. She added that clots are a common problem in cancer patients -- regardless of the type of treatment they receive -- and that such clots typically can be treated or prevented with blood-thinning medications.

According to USA Today, many physicians "had hoped drugs such as Avastin, which can cost up to $55,000 a year for breast cancer, might spare patients from the miseries of traditional chemotherapy, including nausea, crushing fatigue and life-threatening infections." Nevertheless, few patients benefit from Avastin alone and, in most cases, patients treated with the drug continue to take the older chemotherapies, which means patients may develop more side effects rather than fewer. Neal Meropol of Philadelphia's Fox Chase Cancer Center -- who was not involved in the study -- said that serious side effects are much less common with Avastin than with traditional chemotherapies, adding that he believes most physicians will continue to prescribe the drug. Meropol added that he hopes the study will encourage research into methods for preventing and treating blood clots, such as prescribing low-dose aspirin before the clots form (Szabo, USA Today, 11/19).

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