The American Cancer Society estimates that in 2004, almost 150,000 Americans will develop colorectal cancer , and over 50,000 will die from it. Colorectal cancer is most commonly treated by surgery, radiation therapy , and/or chemotherapy . In addition, new, targeted drug therapies called monoclonal antibodies are being used as well.

A cancerous tumor cannot grow unless it establishes its own blood supply through which the tumor can get the oxygen and nutrients it needs to grow and spread. Bevacizumab (Avastin) is a monoclonal antibody that targets vascular endothelial growth factor (VEGF), a naturally occurring protein that stimulates the creation of new blood vessels. When VEGF is bound to bevacizumab, new vessel formation is inhibited, and tumor growth is slowed.

Avastin was approved by the Food and Drug Administration (FDA) for the treatment of colorectal cancer in February 2004, after it was shown to extend colorectal patient’s lives when used in combination with chemotherapy. A new study in the New England Journal of Medicine found that colorectal cancer patients who received standard chemotherapy plus bevacizumab had significant increases in survival, compared with patients who received standard chemotherapy plus placebo.

About the Study

This study included 813 people with untreated metastatic colorectal cancer (colorectal cancer that has spread to other parts of the body). Approximately half of the participants (402) were randomly assigned to receive standard chemotherapy (irinotecan, fluorouracil, and leucovorin) plus bevacizumab (treatment group), while the other half (411) received the same chemotherapy plus a placebo pill (control group).

The researchers assessed the participants’ tumor status every six weeks for the first 24 weeks of the study, then every 12 weeks thereafter. To monitor the safety of the treatment combination, the researchers kept track of reports of adverse events, laboratory test results, and vital sign measurements throughout the study.

The researchers followed the participants to determine overall survival, progression-free survival (time before cancer begins to grow again), and treatment response and safety.

The Findings

The researchers found that after one year, the survival rate in the treatment group was 74%, while the survival rate in the control group was 63%. Overall survival was significantly longer in the treatment group than in the control group (20.3 months versus 15.6 months, respectively), and the participants in the treatment group had a 34% reduced risk of death, compared to those in the control group.

Progression-free survival was also significantly longer in the treatment group compared to the control group (10.6 months versus 6.2 months, respectively). Furthermore, the duration of the response to treatment was 10.4 months in the treatment group, compared to 7.1 months in the control group.

Participants in the treatment group experienced about 10% more adverse events than those in the control group. This effect was largely attributed to high blood pressure requiring treatment, diarrhea , and leukopenia (low white blood cell count). In addition, six participants (1.5%) in the treatment group—but none in the control group—developed a gastrointestinal perforation (a whole in the wall of the stomach or intestine).

It is important to note that this study was funded by Genentech, which is the pharmaceutical company that manufactures Avastin.

How Does This Affect You?

These findings suggest that bevacizumab, when used in conjunction with chemotherapy, should be considered a promising option for the treatment of metastatic colorectal cancer. This is exciting, since it is the first time in decades that a new treatment has been shown to extend survival in patients with this type of cancer.

The benefits of bevacizumab shown in this study are both statistically significant and clinically meaningful. More research will investigate the potential risks (i.e., high blood pressure, gastrointestinal perforation) associated with bevacizumab, but for now, the benefits of this drug seem to outweigh the risks. For many people facing the diagnosis of metastatic colorectal cancer, the availability of a life-extending therapy can be very comforting.

Beyond supporting the use of this drug in colorectal cancer patients, this study highlights the notion that bevacizumab and other monoclonal antibodies may be useful in treating other cancers. By targeting naturally occurring growth factors in the body, these drugs can increase the effectiveness of traditional therapies, and slow the growth and spread of existing cancers. These drugs—and others on the horizon—will likely lead to a dramatic change in cancer treatment as we know it today.