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Monitoring for Patients Receiving Herceptin for Breast Cancer

Among patients with HER2-positive breast cancer who are being treated with Herceptin (trastuzumab), monitoring for cancer spread (metastases) to the brain may be beneficial . These results were recently published in Annals of Oncology.

HER2-positive breast cancer is a category of breast cancer accounting for approximately 20% of all breast cancers. It refers to the cancers expressing too many HER2 proteins on the surface of their cells.

HER2 proteins are involved in a biologic pathway associated with cellular replication, growth and spread. Agents targeted specifically against the HER2-protein, such as Herceptin, have improved outcomes for patients with HER2-positive breast cancer.

The brain is a fairly common site of metastases for many types of cancers. The brain and spinal cord are covered by a thin membrane referred to as the blood-brain barrier. This barrier protects the brain and spinal cord as it only allows certain substances to pass through.

One difficulty in creating agents to protect against, or treat, brain metastases, is that many drugs are not able to permeate the blood-brain barrier. Therefore, these agents are not able to confer protective or treatment effects to the brain or spinal cord as they are able to within the rest of the body.

Researchers believe that larger-sized drugs, such as Herceptin, might not be able to pass through the blood-brain barrier and thus are not able to provide benefit to the brain and spinal cord of patients taking the drug. Furthermore, researchers speculate that brain metastases of HER2-positive breast cancer patients might not express as many HER2 receptors on their surface. Both of these issues lead to less effective effects of Herceptin on the brain than for the rest of the body in these patients.

Researchers from the Ohio State University Comprehensive Cancer Center recently evaluated data from over 9,000 patients with HER2-positive breast cancer who were involved in different clinical studies.

The first site of metastasis being in the brain versus other sites in the body among these women was significantly increased for those treated with Herceptin versus those not treated with Herceptin.
The initial site of metastasis being in the brain versus other sites in the body among HER2-positive breast cancer patients appears to be higher among women treated with Herceptin compared to those not treated with Herceptin. These results do not suggest that Herceptin increases the risk of brain metastasis; it only suggests that Herceptin does not confer the protective effects in the brain as it does for the rest of the body.

Researchers continue to explore reasons for this, such as the potential that Herceptin does not permeate the blood-brain barrier, as well as to evaluate other targeted agents and associated effects on brain metastasis. Patients taking Herceptin may wish to speak with their physician regarding monitoring for brain metastases, so they can be treated in their earliest stages.

Reference: Olson E, Abdel-Rasoul M, Maly J, et al. Incidence and risk of central nervous system metastases as site of first recurrence in patients with HER2-positive breast cancer treated with adjuvant trastuzumab. Annals of Oncology. 2013. doi: 10.1093/annonc/mdt036. First published online: March 4, 2013.