Appendix A Case Study: The Role of Biospecimens for Discovery of a Targeted Cancer Therapy Human epidermal growth factor receptor-2 (HER2; also called ErbB2 or Neu) is a cell-surface protein involved in cell development. In normal cells, HER2 controls aspects of cell growth and division. Activation of HER2 in cancer cells, however, accelerates many cellular processes associated with tumor formation, including cell proliferation, angiogenesis, adhesion, and resistance to chemotherapy. In 1987, Dennis Slamon and colleagues examined tumor samples from 189 breast cancer patients enrolled in an ongoing study and discovered that the gene that codes for HER2 is amplified in 20 to 30 percent of human breast cancers. Two years later, upon examining the gene and its RNA and protein products in more than 650 frozen and paraffin-embedded human breast cancer samples, Slamon and colleagues demonstrated that amplification of the HER2 gene correlates strongly with poor clinical prognosis. Slamon also observed that tissue samples subjected to freezing processes retained more protein activity for analysis than did samples prepared using paraffin-based or other fixative methods. As a result of these groundbreaking observations, which were made possible by the use of tissue specimens, HER2 has subsequently become a pivotal biomarker in breast cancer and has promoted the development of the revolutionary anti-cancer drug, trastuzumab. The development of trastuzumab (Herceptin®; Genentech, San Francisco, CA) is a success story that demonstrates the potential of biomarkers in the rational design and development of cancer drugs. Trastuzumab is a recombinant monoclonal antibody directed against the extracellular domain of HER2. Designed specifically for those breast cancer tumors that overexpress HER2, trastuzumab has been highly effective as a single agent and in combination with other standard chemotherapy regimens for certain types of breast cancer. Based on trastuzumab’s clinical trial success, the FDA approved the drug for treatment of HER2-positive metastatic breast cancer in 1998. However, in all clinical trials with trastuzumab prior to approval, the antibody was studied only in patients whose tumors tested "HER2-positive." This classification was determined using a set of research-grade immunohistochemistry (IHC) assays, in which the tissue sample is treated with an antibody specific to the protein of interest. This antibody binds to the protein and is then reacted with a second, specific antibody that contains a fluorescent or chemiluminescent "tag," allowing the protein-antibody complex to be visualized as it naturally appears in the tissue. Access to banked tissue samples proved pivotal in translating these research assays into an FDA-approved assay (HercepTest) that could be used in a wide range of pathology laboratories. NCI’s Cooperative Breast Cancer Tissue Resource provided 1,200 specimens that were used to demonstrate adequate concordance between the test methods. Following initial approval of trastuzumab, the development of more sophisticated approaches to assess HER2 status has confirmed that patients who display high levels of HER2 overexpression (measured using IHC) or an amplification of the HER2 gene (measured using fluorescence in situ hybridization (FISH) techniques) receive the greatest clinical benefit from the drug. In one clinical trial evaluating trastuzumab as monotherapy in women with advanced metastatic breast cancer, all responding women who were moderately IHC-positive also tested FISH-positive, suggesting that the combination of IHC and FISH can further identify patients who may benefit from trastuzumab. Access to tissue samples has proven crucial to the development of trastuzumab, from the initial observation that linked HER2 level with poor outcomes in metastatic breast cancer to the identification of target patient populations for clinical trials and response to therapy with the approved drug. The success of trastuzumab proves that biomarker-based patient selection at an early stage in the clinical trial process can optimize the development of successful cancer therapy. In retrospect, the clinical benefits of trastuzumab would almost certainly have been insufficient for FDA approval if the agent had been tested in unselected patient populations. Moreover, molecular insights gained from clinical trials with trastuzumab will promote research with new biomarkers, as well as the development of future therapies using monoclonal antibodies and other rationally designed drugs.

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