Standard management in the treatment of many solid tumors has improved in recent years, yet many metastatic solid tumors remain incurable. Factors that limit the success of treatment include drug resistance and lack of tumor selectivity. Although progress has occurred in cytotoxic therapy for breast cancer, interest in new interventions continues. Because of the ability of the immune system to target specific responses, the area of immunotherapy has great potential in future management of cancer.

This update includes material presented at a symposium sponsored by the European Oncology Nursing Society, as part of the 1999 European Cancer Conference in Vienna, Austria.

Research focusing on nonspecific immunotherapy had modest beginnings in the 1960s and 1970s. As we reach the turn of the century, public and political pressure to search for the "magic bullet" for cancer treatment continues to drive scientists at an ever-increasing pace. Important findings in immunology have had significant bearing on cancer diagnosis and treatment, particularly in regard to breast cancer. Research in this field has led to a far greater understanding of how cells function, proliferate, differentiate, and survive. Many cellular growth factors have been identified and are being isolated as a means to control, suppress, or eliminate cancer cells.

The immune system functions with a high degree of specificity and sensitivity. Each immunoglobulin/antibody is designed to react to a specific corresponding antigen. The biological effects of this reaction result in neutralization or elimination of an antigen. As a result, scientists have studied antibodies as vehicles for therapeutic targeting for many years. As the science in this field has evolved, monoclonal antibodies (antibodies produced by a single cell that is specific for a given antigen) have proven most capable of binding to tumor antigens with a high degree of specificity.

This heightened understanding of the immune system, the development of methods to evaluate aspects of the immune response, and the development of monoclonal antibodies has transformed the field of immunotherapy. In the future, advances related to humanized monoclonal antibody that are directed at amplified HER2 growth factor receptors are certain to be among the first of many biologicals that will be used in breast cancer treatment.

HER2 is an acronym for human epidermal growth factor receptor, also known as c-erbB-2/neu. Growth factors are protein products of genes called proto-oncogenes, which are fundamentally important for normal cells. The proto-oncogenes interact with other genes and their products; these genes, called tumor suppressor genes, also have important roles in normal cell division. Tim Cooke,^[1] professor of surgery at the University of Glasgow, Scotland, described how malignant transformation can occur with the alteration in one of these genes, such as the loss of a tumor suppressor gene or mutation or amplification of proto-oncogenes, resulting in uncontrolled cell proliferation.

HER2 is a proto-oncogene found on chromosome 17. It encodes a protein and functions as a cell membrane receptor (see Figure 1). HER2 is one of a family of 4 structurally related receptors.^[2] The HER family plays an important role in regulating cell growth, survival, and differentiation in a complex manner.

Figure 1. Model of the HER2 protein. © Gardiner-Caldwell Communications Ltd. 1999.

The HER2 receptor has no identified ligand but is able to form a heterodimer, or a compound formed by the union of 2 differing molecules of simpler compounds, with other members of the HER2 family. Ligand binding to this heterodimer receptor complex on the cell surface leads to activation of intrinsic protein tyrosine kinase activity, triggering a cascade of events. This results in the transmission of signals across the cell membrane and across the intracellular space to the nucleus, where gene activation occurs.^[3,4] Figure 2 depicts the steps in growth factor signal transduction. Understanding these receptors and identifying their ligands and the resulting signal transduction pathways represent a major conceptual advance.^[5-7] Several steps in these pathways are currently being targeted for therapeutic intervention, including tyrosine kinase inhibitors.^[8]

Figure 2. Steps involved in growth factor signal transduction. © Gardiner-Caldwell Communications Ltd. 1999.

All normal epithelial cells contain 2 copies of the HER2 gene and express low levels of HER2 receptor on the cell surface. In some cases, during oncogenic transformation the number of gene copies per cell is increased, leading to an increase in mRNA transcription and a 10- to 100-fold increase in the number of HER2 receptors on the cell's surface, called overexpression (see Figure 3).

Figure 3. Indicators of HER2 status: gene or DNA amplification and mRNA or protein overexpression. © Gardiner-Caldwell Communications Ltd. 1999.

In vitro and animal studies indicate that HER2 gene amplification and protein overexpression play a pivotal role in oncogenic transformation, tumorigenesis, and metastasis. Transfection (the incorporation of exogenous DNA into a cell) of the HER2 gene into human breast and ovarian tumor cell lines produced more aggressive growth characteristics, such as increased DNA synthesis, cell growth, growth in soft agar in vitro, tumorigenicity, and metastatic potential in nude mice.^[9,10] (see Figure 4). Dr. Cooke also pointed out that the growth of tumors and human breast cancer cell lines that overexpress the HER2 receptor is inhibited by anti-HER2 monoclonal antibodies, further indicating the role of HER2 gene amplification/receptor overexpression in oncogenesis.

Figure 4. HER2 overexpression following transfection of human MCF-7 breast cancer cells with HER2 DNA and phenotypic transformation. © Gardiner-Caldwell Communications Ltd. 1999.

Gene amplification/receptor overexpression has been demonstrated in breast, ovarian, bladder, gastric, and pancreatic tumors. Gene amplification is associated with aggressive cell behavior and poor prognosis (see Figure 5). It has also been suggested that overexpression may be associated with resistance to tamoxifen.^[11] Some tumors show receptor overexpression without gene amplification and have a more favorable prognosis, yet the biologic significance of this variant is less certain.

In general, the presence of HER2 amplification/overexpression appears to be a key factor in malignant transformation and is predictive of a poor prognosis in breast cancer.

Figure 5. Disease-specific survival and HER2 expression. Courtesy of Prof. T.G. Cooke.

Breast cancer was the first tumor type in which abnormalities of HER2 gene copy number and/or expression were associated with reduced disease-free and overall survival. Scientists have focused on HER2 over the past 20 years and have succeeded in confirming overexpression. Patricia Rovelon,^[1].a nurse from the Institut Gustav Roussy in Villejuif, France, pointed out that HER2 is universally accepted as a new prognostic marker and predictor of therapeutic response. But she and other speakers cautioned that the prognostic value of HER2 varies, depending on the assay method used.^[12]

Test methods. Leaders in the field of HER2 have stressed the importance of developing a simple and accurate method of determining HER2, one that is both inexpensive and reproducible. The 2 techniques currently used to measure HER2 gene copies are quantitative polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). The process for PCR is fully automated and requires only minimal amounts of tumor tissue. This method will allow retrospective studies to be performed with archival tissue. FISH also only requires small tissue samples, and has extreme sensitivity to detect amplification from a histologic section.^[13] However, FISH is not widely available in hospital laboratories. The result of this method can vary considerably if the assay is not standardized, and is thereby dependent on the skill of the pathologist.

A more widely used test is immunohistochemistry (IHC), which measures HER2 protein expression. IHC has been specifically adapted for detection of HER2 protein using specific antibodies. The advantages to this method are that it can be used on fresh and archival tissue and that it utilizes technical and human resources readily available in pathology laboratories. Unfortunately there are some disadvantages to this method. IHC uses different antibodies with different binding affinities and different epitope specificities, thereby creating differences in HER2 overexpression rates. In addition, HER2 overexpression scoring systems differ and often rely on subjective measures of staining intensity and pattern. When IHC staining techniques that are too sensitive are employed, it becomes problematic to differentiate between normal versus the high HER2 protein levels that are associated with gene amplification.

The enzyme-linked immunosorbent assay (ELISA) is another method of testing HER2 protein in serum samples. While the technology is simple and well suited to automation, it may produce significantly different results to those obtained with IHC and FISH. While IHC and FISH measure HER2 receptor protein (mostly intracellular) and gene amplification respectively, ELISA specifically measures levels of the extracellular HER2 receptor proteins released into the plasma from HER2 overexpressing tumors.^[14,15]

It is widely acknowledged that the ideal test for HER2 status is one that is simple to perform, specific, sensitive, standardized, stable over time, and allows archival tissue to be assayed. At present the test that best meets these criteria is IHC. With standardization of laboratory testing and appropriate quality control in place, the reliability of IHC will be improved further. It is expected that FISH will become more widely used in the future as well.

The oncology nurse's role. It is important for oncology nurses who counsel patients to be fully aware of the advantages and disadvantages of the various testing methods and the impact that these test methods and results may have in terms of prognosis and treatment for the patient. This may require detailed communication with the pathologist about how the test sample was obtained, clarification with the laboratory about the test method employed (and its potential variability), and discussion with the oncologist to interpret the results. Knowledge of testing methods and a determination of the accuracy of results is critical to appropriately identify patients that may benefit from anti-HER2 therapies.

The prognosis of breast cancer can be assessed using variables including tumor type, size, and grade; lymph node status; degree of vascular invasion; estrogen and progesterone receptor status; cell proliferation index; S phase; DNA ploidy; and growth factors. Yet it is widely acknowledged that tumor grade, lymph node status, and hormone receptor status are the variables that carry the most predictive weight for prognosis. Using a combination of factors is most helpful. End-point measures of disease-free survival (DFS) and overall survival (OS) generally determine prognosis.

The HER2/neu proto-oncogene is amplified and as a result overexpressed in 25%-30% of human breast cancers.^[16,17] This finding is associated with a more aggressive form of the disease, in that women whose tumors contain amplification/overexpression have shorter DFS and OS.^[16-18]

Along with the other factors used to determine prognosis, the presence of HER2 amplification/overexpression is associated with more aggressive forms of the disease (found in 25% to 30% of all breast cancers) and can be indicative of a shorter disease-free period and overall survival.

Nursing assessment. Many patients who are currently being tested for HER2 status are women with metastatic breast cancer who have been heavily pretreated. Therefore, it is important to gather information about the patient's health history, performance status, all prior treatments, emotional well being, as well as the understanding of the disease status, the meaning of HER2 testing, and its possible implications. Nurses may collaborate with other practitioners in obtaining any or all of this information. It is also critically important to involve family members in the process of gathering accurate and thorough information.

Dennis Slamon,^[1] MD, chief of the Division of Hematology-Oncology at UCLA's Jonsson Comprehensive Cancer Center, is a central figure in the study of HER2 and anti-HER2 therapies. In multiple presentations at the 1999 ECCO conference, he provided a brief historical summary of early studies and the course taken by researchers over the last several years. Once HER2 overexpression was identified as a factor in breast cancer, subsequent studies demonstrated that this alteration was found to play a direct role in causing the aggressive phenotype.^[10,21-23] Consequently, studies designed to evaluate therapeutic targets to HER2 amplification/ overexpression followed.^[21-25]

Monoclonal antibodies studied in mice were found to have positive antitumor activity but showed limited results when administered in humans due to immune response to the nonhuman protein. Trastuzumab humanized monoclonal anti-HER2 antibody (rhuMAb HER2, Herceptin) was produced. Phase I and II trials demonstrated that trastuzumab is well tolerated and produced responses both alone and in combination with cisplatin.^[26,27].

The mechanism of action for trastuzumab remains unknown but is believed to be multidimensional. Possible effects include down-regulation of HER2 overexpression, accelerated receptor degradation, disruption of receptor heterodimer formation, altered signal transduction, and induction of antibody-dependent cell-mediated cytotoxicity.

Early trial results provided the rationale to study trastuzumab as a single agent and in combination with chemotherapy in pivotal phase II and III clinical trials conducted by Slamon and his colleagues.^[28-30] The first of these was an open-label multinational trial of single agent trastuzumab given to 222 HER2-overexpressing metastatic breast cancer patients.^[28] The overall response rate in the trastuzumab-treated patients was 15%, with 6 confirmed with a complete response and 25 confirmed with partial responses. Median duration of responses was 8.4 months and median survival was 13 months.

The second and more definitive study evaluated 469 women who were treated with first-line therapy for metastatic disease with either chemotherapy alone (6 cycles of anthracyline plus cyclophosphamide or, if they had received prior adjuvant anthracyclines, paclitaxel) or trastuzumab plus chemotherapy.^[29,30] An important note is that women who received chemotherapy alone and failed the treatment had the option to cross over to receive trastuzumab at the end of the study. Despite this potential bias, Dr. Slamon was pleased with the results. At 29 months of follow-up, the following results were demonstrated:

1. Time to disease progression and median response duration were significantly longer in the trastuzumab plus chemotherapy group than in the group receiving chemotherapy alone.
2. Overall response rate (50% vs 32%) and overall survival duration (25.4 vs 20.3 months) were significantly greater in the trastuzumab plus chemotherapy group.
3. One-year survival rates differed significantly between the 2 groups: 78% in the trastuzumab plus chemotherapy group versus 67% in the chemotherapy alone group.
4. Responders in the trastuzumab plus chemotherapy group survived a median of 10 months longer.

It should be noted that cardiotoxic effects have been reported in regard to trastuzumab. The cardiotoxicity was most severe when trastuzumab was administered with anthracyclines. The evidence suggests that trastuzumab alone is not cardiotoxic, but it may be when used with, or proximal to, an anthracycline.

In markets where it is approved for clinical use, trastuzumab is indicated as a single agent for the treatment of women with HER2- positive metastatic breast cancer who have received prior chemotherapy for metastatic disease. It can also be used in combination with paclitaxel for the first-line treatment of women with HER2-positive metastatic breast cancer. Christel Bohme,^[1] an oncology research and liaison nurse at Kantonsspital, St. Gallen, Switzerland, reviewed how anti-HER2 therapy is administered, as well as subsequent side effects and their management.

Administration. Trastuzumab is administered as a 4 mg/kg loading dose by IV infusion over 90 minutes in normal saline, followed by weekly 2 mg/kg maintenance doses administered by IV infusion over 30 minutes. As with other biologic therapies, trastuzumab should not be given by IV bolus or push.

Routine monitoring of vital signs is necessary. Optimal treatment duration has not been determined, but trastuzumab is generally given until there is evidence of progression of disease. It is recommended that the initial treatment be closely monitored in the hospital; all subsequent treatments can be safely administered in an outpatient setting. It is important that the physician as well as the nurse be very familiar with the properties of this therapy.

Side effects/precautions. In contrast to the many traditional chemotherapeutic agents for breast cancer, trastuzumab is very well tolerated. Severe nausea and alopecia have not been reported, and myelosuppression is rare. In both the phase II single agent^[28] and phase III combination study,^[29,30] the most common adverse events were mild to moderate fever and chills. These side effects occurred primarily during initial administration and did not occur during subsequent treatments, and they were easily managed with antipyretics. It is important to note that because trastuzumab is well tolerated and easily administered, this therapy has a minimal impact on nursing workload.

Experts who have the most experience with trastuzumab suggest that cardiac monitoring is necessary. The incidence of cardiac dysfunction was highest in the combination trial, particularly for those receiving trastuzumab plus anthracycline. Severe cardiac dysfunction (NYHA class III/IV) was 16% in patients receiving anthracyclines plus trastuzumab compared with 3%, 2%, and 1% in those receiving anthracyclines alone, paclitaxel plus trastuzumab, and paclitaxel alone, respectively. In both the phase II and phase III trials, 70%-80% of the patients who developed cardiac dysfunction continued to receive trastuzumab, and the majority either stabilized or improved with standard cardiac management. Given these findings, a thorough cardiac history and work-up is warranted for patients before they receive this therapy.

Quality of life. A critical end point in current studies relates to quality of life (QOL). In patients for whom QOL data are available,^[31] trastuzumab monotherapy maintained QOL until disease progression and improved global and social function scores. In patients who responded to trastuzumab therapy, health-related QOL improved.

As with all new therapies, the monitoring of QOL measures is critical. This is an ideal area for nursing involvement in trials; oncology nurses should become familiar with QOL measurement tools, learn about previous QOL studies relating to HER2, and ensure accurate and consistent data collection.

Patient and family education. Nurses are ideally suited to be the medical liaison to patients and their families when embarking upon anti-HER2 therapy. They can provide the education and support needed to inform and guide patients through clinical trials with trastuzumab. Patients need to be informed of the potential extent of benefit expected with the treatment and should receive information regarding the administration, potential side effects, and follow-up required.

Teach patients and family that trastuzumab:

• acts specifically on cancer cells and has no significant effect on normal cells;
• significantly improves overall survival in women with HER2-positive metastatic breast cancer, offering new hope for patients;
• does not interact adversely with concomitantly administered drugs; and
• does not negatively affect patient well being, unlike cytotoxic chemotherapy.

The ability to identify HER2-positive patients and offer them anti-HER2 therapy has significantly changed the treatment for that subgroup of metastatic breast cancer patients. Such advances have allowed for very individualized treatment planning, thereby eliminating potentially unnecessary interventions.

To realize this potential, patients with HER2 overexpression must be accurately identified. Reliable, standardized, and accurate testing is essential. It is important that HER2 status is determined at the time of diagnosis, because this information will become increasingly important in the management of patients with both primary and metastatic breast cancers. Patients need to be informed of the potential extent of benefit expected with the treatment, and therapy must be used optimally.

Researchers in the area of HER2 are enthusiastic about the potential for further advances toward the treatment of both adjuvant and metastatic breast cancer. With HER2 testing and the responses seen with anti-HER2 therapy, it is likely that we will see trastuzumab introduced into adjuvant therapy trials. New information is also emerging regarding the increased activity seen when trastuzumab is combined with platinum salts.

Although it is not yet understood when or why the alteration in HER2 expression takes place, Dr. Slamon believes that they are coming very close to knowing when it occurs. This information would undoubtedly lead to more exciting new studies and perhaps new therapies for this difficult-to-treat patient group.

Progress in the field of growth factors, gene therapy, angiogenesis, and other therapies has led to novel treatments for breast cancer. Therapies such as trastuzumab will continue to play an increasing role and may eventually replace some therapies used today. While optimism is warranted, it must be acknowledged that many challenges remain to further understand and improve the treatment of breast cancer. To ensure optimal outcomes for our patients, practitioners will be challenged to maintain and update their knowledge base as new therapeutic advances come to the forefront.

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27. Pegram MD, Lipton A, Hayes DF, et al. Phase II study of receptor-enhanced chemosensitivity using recombinant humanized anti-p185 HER2/neu monoclonal antibody plus cisplatin in patient with HER2/neu-overexpressing metastatic breast cancer refractory to chemotherapy treatment. J Clin Oncol. 1998;16:2659-2671.
28. Cobleigh MA, Vogel CL, Tripathy D, et al. Multinational study of the efficacy and safety of humanized anti-HER2 monoclonal antibody in women who have HER2-overexpressing metastatic breast cancer that has progressed after chemotherapy for metastatic disease. J Clin Oncol. In press.
29. Slamon D, Layland-Jones B, Shak S, et al. Addition of Herceptin® (humanized anti-HER2 antibody) to first line chemotherapy for HER2 overexpressing metastatic breast cancer (HER2+/MBC) markedly increases anti-cancer activity: a randomised multinational controlled phase III trial. Proc Am Soc Clin Oncol. 1998;17:98a. Abstract 377.
30. Slamon D, Layland-Jones B, Shak S, et al. Concurrent administration of anti-HER2 monoclonal antibody and first-line chemotherapy for HER2-overexpressing metastatic breast cancer: a phase III, multinational randomized, uncontrolled trial. N Engl J Med. 1999. In press.
31. Lieberman G, Burchmore MJ, Ferhenbacher L, Cobleigh M. Health related quality of life (HRQL) of patients with HER-2 overexpressing metastatic breast cancer (MBC) treated with Herceptin® (trastuzumab) as a single agent. Proc Am Soc Clin Oncol. 1999;18:417a. Abstract 1613.