Are patterns of HER-2/neu amplification and expression among primary tumors and regional metastases indicative of those in distant metastases and predictive of Herceptin response?

Abstract

HER-2/neu (ERB-B2), a member of the receptor tyrosine kinase superfamily, is altered by gene amplification and/or protein overexpression in a wide variety of human epithelial malignancies. Such alterations activate signaling systems that promote cell growth, angiogenesis, cancer metastases, and other procarcinogenic pathways (1). These HER-2 abnormalities are found in approximately one third of breast cancers. HER-2 “status” is a loose and suboptimal term that is commonly used to describe the degree of HER-2 gene amplification and/or the extent of Her-2 protein overexpression. HER-2 status has been used as a marker for breast cancer prognosis (in addition to the classic markers lymph node status, tumor size, type and grade, hormone receptor status, and proliferation rate), because, in the majority of cases, HER-2 alterations independently portend a worse outcome. In addition, associations have been found between the degree of HER-2 expression or gene copy number and the likelihood that a patient may derive benefit from some chemotherapy regimens, i.e., predictive value (2–4). Statistically significant interactions between HER-2 status and chemotherapeutic agents other than anthracyclines have also been reported (5). Given these chemotherapeutic/HER-2 interactions and new anti-HER-2 therapeutic agents, it is no longer always correct to assume that cancers with an altered HER-2 status will have a poor outcome. As noted, HER-2 has become an important target for novel therapeutic strategies, such as trastuzumab (Herceptin), a monoclonal antibody that acts as an HER-2 antagonist. This agent has shown promise in treating a subset of patients with otherwise chemorefractory, late-stage breast cancer. Many recently opened breast cancer trials combine Herceptin with other agents to treat various stages of disease. There are several laboratory methods to evaluate HER-2. These include fluorescent in situ hybridization (FISH), to determine HER-2 gene copy number, reverse transcription– polymerase chain reaction, to measure HER-2 messenger RNA levels, and immunohistochemical (IHC) analysis, to detect overexpressed HER-2. Any or all of these methods can be used to determine the HER-2 status of a given tumor. The majority of these methods use a single sample of formalin-fixed tissue from the primary breast cancer. However, it remains unclear which method, reagent, or protocol provides superior prognostic or predictive data. None of these methods determine whether the effectors downstream of HER-2 are activated, whether HER-2 is bound to the EGF receptor (erbB-1) or to its other dimerization partners, whether HER-2 is phosphorylated and thus in its activated configuration, or whether HER-2 is internalized or recycled to the membrane. Assays that could delineate these important and biologically relevant variables or pathways, or a single sentinel test to better assess the functional status of the receptor, need to be developed. The study by Simon et al. (6) in this issue of the Journal utilizes both IHC and FISH to determine the HER-2 status of primary breast tumors and regional (axillary) metastases. The study was designed to compare HER-2 data derived by each method as well as the HER status of primary breast cancers and their associated metastases. The reader should be clear that, in this study, the metastases being analyzed are regional, concurrent lymph node metastases from the primary cancer rather than distant (usually visceral or bony) metastases. One should not assume that the two types of metastases are equivalent, since distant metastases often represent clonal outgrowths with genetic and other modifications that are often identified years after resection of the primary cancer. Furthermore, cells that metas-