Breast Cancer: The Test Case
Hormone receptor (HR) status has been used to direct the treatment of breast cancer for 20 years. But in the past two years,
new biomarker-based tests have emerged to identify patients at low risk of recurrence. The first tests are for RNA detection
or for the identification of DNA copy number changes in tumor samples; these latter tests can accurately identify low risk
of recurrence in both HR positive and HR negative patients. The advent of biomarker testing will undoubtedly have an impact,
according to Hans Winkler, PhD, senior director of functional genomics for Johnson & Johnson, who suggested in his presentation
at the 2005 Biomarker World Congress that in the future, it may take five drugs to treat breast cancer—one for each subtype.
But getting physicians to use specific biomarker-based tests takes time, proof in practice, and education, as evidenced by
the seven-year history of HER2/neu testing to define which patients should be treated with Genentech's Herceptin (trastuzumab).
Today, physicians sometimes refer to "HER2 disease," and HER2/neu testing is ordered routinely.
Tests like the HercepTest with Herceptin, and EGFR pharmDx with Erbitux (cetuximab), have focused almost exclusively on the
question of: "Which patients will benefit from a specific treatment?" It remains to be seen how EGFR testing might be used
for Erbitux, Tarceva (erlotinib), or Iressa (gefitinib). As an emerging example of a biomarker-based test with the potential
to have an impact on the use of multiple drugs, the Roche AmpliChip CYP450 detects changes in the 2D6 and 2C19 genes to address
the small genetic differences in individuals that result in a significant difference in drug metabolism for some commonly
Suzanne Z. Mattingly, PhD, is vice president, business development and marketing, for
Exagen Diagnostics. She can be reached at email@example.com
Bo E. H. Saxberg, MD, PhD, is founder and president of DDO Strategic Services, LLC. He can be reached