According to the FDA, the recurrence of breast cancer is partly dependent on the activation and suppression of certain genes located in the breast tumor.2 MammaPrint measures the activity of 70 genes associated with breast cancer recurrence from a sample of a surgically removed breast tumor. A complicated algorithm (formula) is then used to produce a risk score that indicates whether the patient is at low or high risk of the cancer spreading to other parts of the body. The risk score can then be used to help decide which treatments are appropriate—a woman with a low risk score may even utilize the test in deciding whether to forgo chemotherapy.
The test has limitations. It is far better at predicting low risk than high risk of recurrence. According to news reports, 23 percent of women with a high risk score had a recurrence of cancer somewhere in the body within five years (a 77 percent false positive rate), whereas only about 5 percent of those with a low risk score had a recurrence (a 5 percent false negative rate).3 The FDA describes the test as “useful in predicting time to distant metastasis in women who are under age 61 and in the two earliest stages of the disease (Stage I and Stage II) and who have tumor size equal to or less than five centimeters and no evidence that the cancer has spread to nearby lymph nodes (lymph node negative).”4
The FDA continues to allow tests developed by and produced in a single laboratory (known as “home brew” tests) to be marketed without approval. Because the FDA does not require formal approval for these tests, Oncotype DX—a “home brew” test—has been in use since 2004. However, the FDA has signaled that it may require approval for all tests, stating in the MammaPrint approval press release, “Several months ago, FDA issued a draft guidance document concerning the need for these complex molecular tests to meet pre-market review and post-market device requirements even when the tests are developed and used by a single laboratory.”5
1 Andrew Pollack, “Test to Predict Breast Cancer Relapse Is Approved,” New York Times, February 7, 2007.
2 Food and Drug Administration, “FDA Clears Breast Cancer Specific Molecular Prognostic Test,” news release, February 6, 2007.