The Oncologist, Vol. 11, No. suppl_1, 34-41, September 2006; doi:10.1634/theoncologist.11-90001-34 © 2006 AlphaMed Press
HER-2-Positive Metastatic Breast Cancer: Optimizing Trastuzumab-Based TherapyDepartment of Gynecology and Obstetrics, Klinikum Offenbach, Offenbach, Germany Key Words. Trastuzumab • Metastatic breast cancer • Combination therapy • Treatment beyond disease progression Correspondence: Christian Jackisch, M.D., Klinikum Offenbach GmbH, Department of Gynecology and Obstetrics, Starkenburgring 66, D-63069 Offenbach, Germany. Telephone: 49-0-69-8405-3850; Fax: 49-0-69-8405-4456; e-mail: christian.jackisch{at}klinikum-offenbach.de Received June 12, 2006; accepted for publication June 21, 2006.
Trastuzumab with a taxane as first-line therapy is now the standard of care for patients with human epidermal growth factor receptor 2 (HER-2)-positive metastatic breast cancer (MBC). The search for additional and more effective trastuzumab-based therapies continues. Novel combinations of trastuzumab with chemotherapeutic agents, including vinorelbine, gemcitabine, and capecitabine, and hormonal therapy agents, such as tamoxifen and aromatase inhibitors, are currently under investigation in clinical trials. Available data suggest these combinations will provide additional treatment options that may ultimately lead to better outcomes for patients with HER-2-positive MBC. Evidence is growing for the use of trastuzumab treatment beyond disease progression and retreatment after (neo)adjuvant relapse is being explored to assist in clinical decision making. Already, the use of trastuzumab in the metastatic setting has changed HER-2-positive status from a marker of poor prognosis to one of better overall outcome, and ongoing studies should expand further the treatment options for patients with HER-2-positive MBC.
Human epidermal growth factor receptor 2 (HER-2) is a transmembrane receptor tyrosine kinase with a key role in normal cell growth and differentiation. Overexpression of HER-2, usually as a result of her-2 gene amplification, can result in malignant transformation of cells and is seen in tumor tissue in up to 30% of patients with metastatic breast cancer (MBC) [15]. HER-2 overexpression is usually associated with a more aggressive tumor phenotype, and women with HER-2-positive disease have a poor overall prognosis and faster relapse times at all stages of cancer development [1, 6, 7]. The advent of trastuzumab (Herceptin®; F. Hoffmann-La Roche, Basel, Switzerland), a humanized monoclonal antibody against the extracellular domain of HER-2, represented a major breakthrough in the treatment of women with HER-2-positive MBC. Pivotal trials of trastuzumab alone or in combination with taxanes have resulted in significant clinical benefit [811], and trastuzumab plus taxanes as first-line therapy is now the standard of care for patients with HER-2-positive disease. In order to further improve patient care, the search for even more effective trastuzumab-based therapies continues in preclinical research and within clinical trials.
The pivotal randomized combination trials of trastuzumab (H0648g and M77001) demonstrated that trastuzumab plus a taxane is associated with a clinical benefit that is superior to that of a taxane alone [9, 11]. Four hundred sixty-nine HER-2-positive MBC patients who had not received prior treatment for advanced disease were enrolled in the H0648g trial. Patients who had previously received anthracyclines in the adjuvant setting or who were not suitable to receive anthracyclines (n = 188) were randomized to receive paclitaxel with or without trastuzumab. All other patients (n = 281) were randomized to receive an anthracycline plus cyclophosphamide with or without trastuzumab. The combination of trastuzumab with paclitaxel or with an anthracycline plus cyclophosphamide improved all clinical end points over paclitaxel or an anthracycline plus cyclophosphamide alone (median follow-up, 30 months). The overall survival duration was longer (22.1 vs. 18.4 months) with trastuzumab plus paclitaxel and with trastuzumab plus an anthracycline plus cyclophosphamide (26.8 vs. 21.4 months ) [9]. Despite these improvements in survival, the number of cardiac events reported in that trial was higher than anticipated from initial clinical data. A retrospective analysis revealed that trastuzumab-associated cardiac events mainly occurred with concomitant use of anthracyclines. Of patients receiving trastuzumab plus an anthracycline plus cyclophosphamide, 28% experienced a cardiac event, compared with only 9.6% receiving an anthracycline plus cyclophosphamide alone [12]. As a result of this finding, the combination of trastuzumab with an anthracycline plus cyclophosphamide is not currently indicated for clinical use. Of patients receiving trastuzumab plus paclitaxel, 13% experienced a cardiac event, compared with 1% receiving paclitaxel alone. This combination is now indicated for use in a number of countries worldwide. In the pivotal trial, trastuzumab plus paclitaxel resulted in a higher objective response rate, 49% versus 17%, and longer time to progression (TTP) and response duration (RD), 6.9 versus 3.0 months and 10.5 versus 4.5 months, respectively [9]. Notably, a subset analysis revealed that trastuzumab plus paclitaxel improved outcomes in patients with immunohistochemistry (IHC) 3+ disease relative to the overall patient population (IHC 2+ and 3+). The median survival time in patients with IHC 3+ disease was 18 months without trastuzumab and 25 months with trastuzumab [13]. The M77001 trial investigated the combination of standard weekly trastuzumab plus weekly or 3-weekly docetaxel in 188 patients with previously untreated MBC. At a 24-month follow-up, the median overall survival time was 22.7 months with docetaxel alone and 31.2 months with trastuzumab plus docetaxel (p = .0062), despite a 57% documented crossover. All clinical outcomes investigated, including the median RD (11.4 vs. 5.1 months) and median TTP (10.6 vs. 5.7 months), were superior for trastuzumab plus docetaxel versus docetaxel alone. Only one patient receiving trastuzumab plus docetaxel experienced symptomatic heart failure (1%). Another patient experienced symptomatic heart failure 5 months after discontinuation of trastuzumab because of disease progression and following treatment with an investigational anthracycline for 4 months [11]. Both pivotal trials demonstrated a favorable safety profile for the combination of trastuzumab with a taxane. The addition of trastuzumab did not significantly add to the toxicity profile of taxanes alone.
There is continuing interest in new trastuzumabchemotherapy combinations, arising from the ongoing aim of improving treatment efficacy. Also, taxanes are increasingly being used in the adjuvant setting, and trastuzumab-based treatment options are needed for patients with MBC who are not candidates for taxane-containing regimens. Combinations of trastuzumab (standard schedule, 4 mg/kg loading dose followed by 2 mg/kg weekly) with agents such as vinorelbine, gemcitabine, and capecitabine have been investigated with encouraging results. Trastuzumab has also been investigated with chemotherapy combinations, including capecitabine and docetaxel, and taxanes and platinum agents.
Trastuzumab Plus Vinorelbine
Trastuzumab Plus Gemcitabine The combination of trastuzumab with gemcitabine in patients with HER-2-positive MBC has also been reported as effective and well tolerated. In a study conducted by the Hellenic Cooperative Oncology Group (HeCOG) [23], 28 patients with HER-2-positive disease received trastuzumab plus gemcitabine (1,000 mg/m2 on days 1, 8, and 15) as salvage treatment after failure of prior chemotherapy with at least one taxane- and/or anthracycline-containing regimen. The overall response rate was 36%, median TTP was 7.8 months, and median overall survival time was 18.7 months (median follow-up, 17.2 months). Similarly, in a phase II study of trastuzumab plus gemcitabine (1,200 mg/m2 on days 1 and 8 every 3 weeks) in MBC patients who had previously received a taxane- and/or anthracycline-containing regimen, the overall response rate in evaluable patients (n = 61) was 38%. The median RD was 5.8 months, median overall survival time was 14.7 months, and median TTP was 5.8 months. These data support the suggestion of additive antitumor activity between gemcitabine and trastuzumab. Moreover, the combination of trastuzumab plus gemcitabine was well tolerated, with no cases of congestive heart failure [24].
Trastuzumab Plus Capecitabine As recent studies have shown a survival benefit for trastuzumab plus docetaxel [11], and also for docetaxel plus capecitabine [29], there is a clear rationale for exploring the combination of trastuzumab plus docetaxel and capecitabine. A randomized trial of trastuzumab plus docetaxel with or without capecitabine in patients with HER-2-positive metastatic or locally advanced breast cancer (Capecitabine, Herceptin, and Taxotere [CHAT]) is currently in progress. An interim safety analysis of CHAT (n = 110) reported a congestive heart failure incidence of 2% [30], which is the same as that reported in recent trials of trastuzumab plus docetaxel [11]. The rate of complicated neutropenia (26%) was also comparable with that seen in previous trials of trastuzumabdocetaxel or docetaxelcapecitabine combination therapy [11, 29]. As of November, 2005, recruitment to CHAT was complete, with 225 patients enrolled, and efficacy results are awaited.
Triple-Combination Regimens
TrastuzumabAnthracycline Combinations Anthracyclines are a mainstay of therapy for patients with MBC; therefore, combination with trastuzumab is an area of active investigation. The significant benefit of adding trastuzumab to an anthracycline (mainly doxorubicin) and cyclophosphamide was clearly demonstrated in the pivotal trastuzumab combination trial (H0648g) [9, 13], despite a higher rate of cardiac events with this combination [12]. For this reason, several studies are examining the cardiac safety of trastuzumab combined with anthracyclines less cardiotoxic than doxorubicin, such as epirubicin or liposomal formulations of doxorubicin. Initial analyses of the Herceptin, Cyclophosphamide, and Epirubicin (HERCULES) trial, a multicenter phase III trial of trastuzumab plus epirubicincyclophosphamide (EC) versus EC alone as first-line therapy for MBC, indicate that, because of its lower potential for cardiotoxic events compared with an anthracyclinecyclophosphamide combination, it is feasible to combine trastuzumab with EC [38]. In phase I of this trial, patients with HER-2-positive disease initially received trastuzumab plus 60 mg/m2 epirubicin (EC60; n = 26). Once it was established that this regimen was not associated with any dose-limiting toxicity, phase II of the trial was initiated. Patients with HER-2-positive disease were then enrolled into an arm of trastuzumab plus 90 mg/m2 epirubicin (EC90; n = 25) and HER-2-negative patients received EC90 alone (n = 24). Both trastuzumab-containing arms met the criteria for acceptable tolerability, with only three patients experiencing a cardiac event: asymptomatic decline in LVEF to <50% in one patient receiving trastuzumab plus EC60 and congestive heart failure in two patients receiving trastuzumab plus EC90. One patient in the EC90-alone arm experienced arrhythmia/ tachycardia. Response rates were 62% for trastuzumab plus EC60 and 64% for trastuzumab plus EC90. This compared favorably with a response rate of 26% in patients with HER-2-negative disease treated with EC90 alone [38]. In the M77035 trial, the efficacy and safety of combining trastuzumab with the liposomal doxorubicin TLC D-99 (Myocet®; Elan Pharmaceuticals, Princeton, NJ) was investigated [39]. By formulating doxorubicin within a liposome, exposure of normal cells to the cytotoxic agent is minimized, resulting in fewer cardiac events. The triple combination of trastuzumab plus paclitaxel (80 mg/m2, weekly) plus TLC D-99 (50 mg/m2, 3-weekly) was generally well tolerated. Two cases of cardiac insufficiency were reported but were not related to study treatment. The combination was also highly active, as evidenced by an objective response rate of 93% in 54 evaluable patients [39].
In estrogen receptor (ER)-positive patient populations, the rate of HER-2 positivity is 11%35% [4042]. In the trastuzumab pivotal trials, approximately 50% of patients with HER-2-positive metastatic disease were also ER positive [43]. Together, these data show that ER/HER-2-copositive disease is common, and it is of interest to explore specific treatment options for these patients. In the pivotal trials, hormone-receptor status did not affect the efficacy of trastuzumab given as a single agent or combined with chemotherapy [811, 44], indicating that trastuzumab is equally effective in ER-negative and ER-positive disease (Fig. 2
Resistance to hormonal therapy, particularly tamoxifen, appears to be a characteristic of ER-positive, HER-2-positive tumors [45], and it has been hypothesized that the addition of trastuzumab to hormonal therapy may overcome this relative resistance. In preclinical studies, the combination of tamoxifen with anti-HER-2 antibodies was shown to produce a greater inhibitory effect on cell growth than either agent alone [46, 47]. There is also some evidence that, compared with tamoxifen, aromatase inhibitors may elicit a greater response in HER-2-positive tumors [48]. Taken together, these findings provide a clear rationale for combining trastuzumab with hormonal agents in patients with HER-2/ER-copositive MBC. Several clinical trials of trastuzumab plus hormonal therapy as first- or subsequent-line therapy in patients with HER-2-positive, ER-positive, metastatic or locally advanced breast cancer are planned or ongoing. Two important phase III randomized trials are nearing completion: first-line trastuzumab with or without letrozole and first-line trastuzumab with or without anastrozole (TrAstuzumab in Dual HER2 ER-Positive Metastatic breast cancer [TAnDEM]). Recruitment to the TAnDEM trial was completed in May of 2004, and results are expected toward the end of 2006. It is anticipated that the results of these trials will help establish the role of trastuzumab in this specific population.
The potential benefit of continuing trastuzumab treatment beyond disease progression with a new chemotherapy partner is a topic of considerable interest in clinical practice. To date, no results from randomized trials have been published; however, preclinical observations and a range of clinical data provide some evidence to support the concept of treatment beyond progression.
In preclinical studies using HER-2-positive human xenograft models, tumor regrowth was observed if levels of trastuzumab monotherapy were not sustained [49]. Also, continuous administration of trastuzumab in combination with a taxane after progression on trastuzumab monotherapy was shown to potentiate the antitumor activity of taxanes even after trastuzumab monotherapy was no longer effective (Fig. 3
Clinical evidence for trastuzumab treatment beyond progression was provided by the H0659g trial, an extension of the pivotal phase III H0648g trial, in which patients were given the opportunity to continue trastuzumab at the time of disease progression, either alone at a higher dose or with a new chemotherapy partner. Prolonged use of trastuzumab was safe and well tolerated and did not appear to increase the risk of cardiac dysfunction. The efficacy of trastuzumab treatment beyond progression was also encouraging, with an objective response rate of 11% and median RD of 6.7 months [51].
Follow-up of patients who progressed on trastuzumab plus docetaxel in a phase II MBC trial reported a median postprogression survival time of 20 months for six patients who continued trastuzumab treatment beyond progression [52], and results from several retrospective analyses of case series also indicate that patients continue to derive benefit from trastuzumab after disease progression [5355]. In a retrospective analysis of patients with HER-2positive MBC, objective response rates and TTP were maintained in patients receiving two or more trastuzumab-based regimens (Table 2
One large randomized trial investigating trastuzumab treatment beyond progression is currently under way: MO17038, a phase III study of trastuzumab plus capecitabine compared with capecitabine alone in women with HER-2-positive MBC progressing after trastuzumab in combination with a taxane or other chemotherapy.
Results from four large-scale global trials have demonstrated that adjuvant trastuzumab reduces the risk of disease recurrence by approximately 50% [5658]. Further to this, the joint analysis of two of these trials demonstrated a significant survival benefit when patients received a total of 1 year of trastuzumab [57]. Based on these groundbreaking results, the use of trastuzumab in the adjuvant setting is becoming standard clinical practice. There is, therefore, a need to determine the optimal treatment regimen for those patients who relapse after adjuvant trastuzumab. The Retreatment after HErceptin Adjuvant (RHEA) retreatment trial is a phase II study of trastuzumab with or without a taxane for the first-line treatment of HER-2-positive MBC in women who have relapsed after (neo)adjuvant treatment with trastuzumab. It is anticipated that data from that trial will provide guidance on how best to treat this important subgroup of patients.
The combination of trastuzumab with chemotherapy is now standard for the first-line treatment of women with HER-2-positive MBC. The use of trastuzumab in the metastatic setting has changed HER-2-positive status from a marker of poor prognosis to one of better overall outcome. In a phase II trial of vinorelbine with or without trastuzumab according to HER-2 expression, women with HER-2-positive disease treated with vinorelbine plus trastuzumab had a better prognosis than patients with HER-2-negative disease treated with vinorelbine alone, thus suggesting that trastuzumab can change the natural history of HER-2positive disease [22]. Novel trastuzumab-containing combinations with additive or even synergistic effects are of great interest, and several are being studied in ongoing clinical trials. Trastuzumab combined with cytotoxic agents such as taxanes, vinorelbine, gemcitabine, and capecitabine has been shown to produce superior response rates, TTP, and overall survival times in patients with MBC, and triplet combinations have the potential to offer additional benefit. Moreover, trastuzumab can be combined with a wide range of chemotherapy regimens while adding little to the toxicity profile of chemotherapy. Cardiac events can occur during trastuzumab treatment but are generally reversible and manageable. However, combinations with anthracyclines are not recommended outside clinical trials and combinations with less cardiotoxic anthracyclines are currently under investigation. HER-2/ER-copositive disease is common: up to 25% of ER-positive tumors are also HER-2 positive. In this population, the combination of trastuzumab with hormonal therapies such as tamoxifen, exemestane, anastrozole, and letrozole is under investigation, and the results from several large clinical trials are eagerly anticipated. Trials of trastuzumab treatment beyond disease progression and retreatment after (neo)adjuvant relapse are also under way, and it is hoped that data from those trials will provide further guidance for clinical practice. The number of trastuzumab-based treatment options in clinical practice is steadily increasing with each new clinical trial. Trastuzumab has become the foundation of care in HER-2-positive disease, and ongoing studies seek to provide further improvements in outcomes, broaden potential treatment approaches, and provide further information about the optimal use in clinical practice.
C.J. has acted as a consultant and performed contract work for Roche within the past 2 years.
The author would like to thank Alan Russell for medical writing support during the preparation of this manuscript.
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