The Oncologist, Vol. 10, No. suppl_3, 20-29, October 2005; doi:10.1634/theoncologist.10-90003-20 © 2005 AlphaMed Press
Extending Survival with Chemotherapy in Metastatic Breast CancerBaylor-Sammons Cancer Center, Dallas, Texas, USA Key Words. Metastatic • Overall survival • Docetaxel • Paclitaxel • Trastuzumab • Bevacizumab Correspondence: Joyce OShaughnessy, M.D., Baylor-Sammons Cancer Center, 3535 Worth St., Collins 5, Dallas, Texas 75246, USA. Telephone: 214-370-1795; Fax: 214-370-1850; e-mail: joyce.o'shaughnessy{at}usoncology.com Received October 3, 2005; accepted for publication October 7, 2005.
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Metastatic breast cancer (MBC) remains essentially incurable, and goals of therapy include the palliation of symptoms, delay of disease progression, and prolongation of overall survival time without negatively impacting quality of life. Anthracycline and taxane-based therapies have traditionally shown the highest degree of activity in MBC. Though numerous randomized clinical trials have shown improvements in overall response rates, few have found clear survival benefits. In recent years, however, there has been a small but growing series of clinical trials demonstrating modest, but meaningful survival advantages in metastatic disease. A common feature in many of these trials has been the use of a taxane, and more recently, a taxane combined with an antimetabolite. In addition, the development of targeted biologic agents active against MBC, such as trastuzumab and bevacizumab, has demonstrated great potential for enhancing the effects of chemotherapy and producing meaningful survival improvements. The role of the taxanes, antimetabolites, and biologics in extending survival in MBC is discussed.
Breast cancer is the most frequently diagnosed cancer in women in the U.S. In 2005, an estimated 211,240 new cases of invasive breast cancer are expected to occur [1]. Continuing on a trend established over the past decade, the overall incidence of breast cancer continues to gradually increase. The mortality rate from breast cancer declined approximately 2.3% per year from 1990 through 2001, due in large part to increased awareness, earlier detection, and improved therapies [1]. Nonetheless, it is estimated that 40,410 women in the U.S. will die of breast cancer in 2005, with breast cancer ranking second only to lung cancer in cancer-related mortality in women. The majority of breast cancer-related deaths are a result of complications from recurrent or metastatic disease. As an initial presentation, metastatic breast cancer (MBC) is uncommon, occurring in only about 6% of newly diagnosed cases [2]. Despite advances in the treatment of breast cancer, approximately 30% of women initially diagnosed with earlier stages of breast cancer eventually develop recurrent advanced or metastatic disease. There is no single standard of care for patients with MBC, as treatment plans require an individualized approach based on multiple factors. These include specific tumor biology, growth rate of disease, presence of visceral metastases, history of prior therapy and response, risk for toxicity, and patient preference. MBC remains essentially incurable, and current goals of therapy are to ameliorate symptoms, delay disease progression, improve or at least maintain quality of life (QoL), and prolong overall survival. Chemotherapy is a treatment option for many patients with MBC. There are a number of agents with established single-agent activity, with the anthracyclines and taxanes generally considered the most active. In addition, capecitabine (Xeloda®; Hoffmann-La Roche Inc., Nutley, NJ, http://www.rocheusa.com), gemcitabine (Gemzar®; Eli Lilly and Company, Indianapolis, http://www.lilly.com), and vinorelbine (Navelbine®; GlaxoSmithKline, Philadelphia, http://www.gsk.com) have also demonstrated substantial activity in the metastatic setting [3]. Selection of agents for treatment is an individualized process. The relative benefits and toxicities of individual agents or combinations must be considered as well as the treatment history and clinical status of the patient. Many patients with recurrent disease will already have had substantial anthracycline exposure from adjuvant chemotherapy, and retreatment with doxorubicin (Adriamycin®; Bedford Laboratories, Bedford, OH, http://www.bedfordlabs.com) or epirubicin (Ellence®; Pfizer Pharmaceuticals, New York, http://www.pfizer.com) is generally avoided. Taxane-based therapy is often considered for patients with anthracycline-pretreated breast cancer; however, it is becoming increasingly common for patients to have received both an anthracycline and a taxane in the adjuvant setting. Time to recurrence is also an important consideration. If time to recurrence is several years following adjuvant therapy, retreatment with prior active agents may be desirable. If progression or disease recurrence takes place in a relatively short time (i.e., <12 months), the use of different classes of classes of agents is generally preferable. Capecitabine, a novel, oral fluoropyrimidine carbamate, has been extensively evaluated in anthracycline- and taxane-pretreated MBC. Four large, multicenter trials have evaluated single-agent capecitabine in patients with MBC that has progressed during or following anthracycline and taxane therapy [48], showing consistent efficacy and safety data. Response rates of 15%26% were demonstrated, with a median survival time of approximately 1 year. Capecitabine demonstrated a favorable safety profile in those trials, with predominant adverse events of cutaneous and gastrointestinal events. Myelo-suppression was particularly rare, as was alopecia. The use of combination therapy versus monotherapy or sequential single agents remains a controversial issue [9]. Depending on the individual patient and specific treatment goals, either can be appropriate. Combination therapies generally result in higher overall response rates and times to disease progression than with sequential single agents, but usually at a cost of greater toxicity. In addition, the higher overall response rates with combination therapy versus sequential single agents may not necessarily translate into superior survival outcomes.
Demonstrating this point are the results of Intergroup trial E1193, in which patients were randomized to receive either paclitaxel (Taxol®; Bristol-Myers Squibb, Princeton, NJ, http://www.bms.com), docetaxel (Taxotere®; Aventis Pharmaceuticals Inc., Bridgewater, NJ, http://www.aventispharma-us.com), or a combination of the two as first-line treatment of MBC [10]. In both the single-agent arms, patients were crossed over to treatment with the alternate single agent at the time of disease progression. Combination therapy produced a significantly higher overall response rate and longer time to treatment failure than either single agent arm; however, there were no differences in overall survival times among the three arms (Table 1
Combinations of traditional chemotherapeutics with targeted biologic agents, such as trastuzumab (Herceptin®; Genentech, Inc., South San Francisco, CA, http://www.gene.com) and more recently bevacizumab (Avastin®; Genentech, Inc.), appear to present a new dimension. With the potential to realize clinical synergism between chemotherapy and the biologics, significant improvements in overall survival with the use of these agents in combination have been seen [1416]. Optimization of chemotherapy for the treatment of MBC remains an ongoing effort. While it is generally accepted that chemotherapy can provide substantial clinical benefit, the potential to positively impact overall survival and QoL remains the subject of debate. This manuscript provides an overview of recent randomized trials in MBC, focusing on survival outcomes and QoL issues.
In the treatment of MBC, there is an underlying assumption that improvements in overall response rates would translate into long-term survival benefits. While there is indirect evidence to support a relationship between response and overall survival [1720], few randomized trials have provided direct evidence. There are indications, though, that with modern chemotherapeutic agents and biologics, progress has been made toward improving survival outcomes in women with MBC. In a population-based analysis of survival outcomes in MBC conducted in British Columbia, the introduction of new agents over the past decade, such as the taxanes, aromatase inhibitors, and trastuzumab, was associated with significant improvements in overall survival times across the population [21]. In addition, there is a small but growing number of randomized clinical trials reporting statistically significant survival improvements in women with MBC [14, 15, 2230]. A common feature of these studies has been the use of a taxane or combination therapy with a targeted biologic agent such as trastuzumab.
Taxanes in Anthracycline-Pretreated Patients with MBC
A survival advantage with the use of single-agent docetaxel in women with anthracycline-pretreated MBC has been observed in two of four randomized phase III trials (Table 2
The second study compared single-agent docetaxel (100mg/m2) with single-agent paclitaxel (175mg/m2) in 449 patients with MBC who had previously received first-line metastatic therapy with an anthracycline-based regimen or had disease progression within 12 months of completing anthracycline-based adjuvant or neoadjuvant therapy [23]. The overall response rate in the intent-to-treat population was 32% with docetaxel, compared with 25% with paclitaxel; this difference did not reach statistical significance. The median time to disease progression and median overall survival time were statistically significantly longer in the docetaxel arm (Table 2 Paclitaxel was also directly compared with albumin-bound paclitaxel (ABI-007) in 460 patients with MBC (who had not received prior paclitaxel or docetaxel for MBC) in a randomized phase III trial [35]. ABI-007 was associated with a significantly greater response rate (33% vs. 19%; p = .001) and time to tumor progression (23 weeks vs. 16.9 weeks; p = .006) than paclitaxel, but median survival rates were similar in the two treatment groups (65 weeks vs. 55.7 weeks, respectively).
Two additional phase III trials compared single-agent docetaxel with either sequential methotrexate and 5-fluorouracil or 5-fluorouracil in combination with vinorelbine (Table 2
Clinical outcomes with taxane combination regimens in anthracycline-pretreated breast cancer patients have been very encouraging, with significant survival benefits observed in two phase III trials [2426]. The first of those trials compared the combination of docetaxel (75 mg/m2) and capecitabine (2,500 mg/m2) with docetaxel alone (100 mg/m2) in 511 patients with disease progression or recurrence following anthracycline-based chemotherapy (Table 3
The incidences of grade 34 adverse events were similar in both treatment groups, and though these rates were relatively high, treatment was generally tolerable. Gastrointestinal adverse events and hand-foot syndrome were more common with combination therapy, whereas febrile neutropenia, sepsis, arthralgia, and myalgia were more common with single-agent docetaxel. QoL scores were similar in the two treatment arms, and overall global health quality was generally maintained over time. For patients treated with docetaxel alone, crossover to single-agent capecitabine was not mandatory. A subsequent survival analysis suggested that patients who received capecitabine following docetaxel had a longer median survival time than patients receiving other poststudy chemotherapy agents [36]. Although retrospective, these data suggest that sequential administration of docetaxel and capecitabine may also have favorable survival outcomes.
The second phase III trial compared the combination of paclitaxel (175 mg/m2) and gemcitabine (1,250 mg/m2) with single-agent paclitaxel (175 mg/m2) in 529 patients with MBC who had previously received an anthracycline but had no prior chemotherapy for metastatic disease [25, 26]. Combination therapy resulted in a significantly higher overall response rate and longer progression-free and overall survival times than single-agent paclitaxel (Table 3
In addition to the E1193 trial, two randomized phase III trials have evaluated a single-agent taxane therapy versus single-agent doxorubicin for patients with MBC without prior anthracycline exposure [38, 39]. The first of these trials compared docetaxel (100 mg/m2) with doxorubicin (75 mg/m2) in 326 patients who had previously received alkylating agent-based therapy, either in the adjuvant setting or for advanced disease [38]. There was no planned crossover design, and further treatment at the time of disease progression was at the investigators discretion. The overall response rate with docetaxel was significantly higher than the rate with doxorubicin, though there were no differences in median time to disease progression or overall survival time (Table 4
A second phase III trial compared paclitaxel (200 mg/m2) with doxorubicin (75 mg/m2) in 331 patients as first-line chemotherapy for metastatic disease [39]. Patients could not have received any prior anthracycline therapy, though prior alkylating agentbased chemotherapy in the adjuvant setting was permitted. At the time of disease progression, patients were to be crossed over to the alternate treatment. The overall response rate and time to disease progression were significantly greater for patients randomized to doxorubicin than for those given paclitaxel, but there was no statistical difference in overall survival time between groups (Table 4
An additional phase III trial compared single-agent paclitaxel (200 mg/m2) with the alkylating agentbased combination of cyclophosphamide, methotrexate, fluorouracil, and prednisone (Deltasone®; Pfizer Pharmaceuticals) (CMFP) in 209 patients as first-line therapy for metastatic disease [27]. Prior adjuvant chemotherapy was permitted. Overall response rates and times to disease progression were not different between the two study arms (Table 4
Seven phase III trials have evaluated a taxane in combination with an anthracycline versus a standard anthracycline-based combination in patients with MBC (Table 5
The combination of doxorubicin (50 mg/m2) and docetaxel (75 mg/m2) (AD) was compared with doxorubicin (60 mg/m2) and cyclophosphamide (500 mg/m2) (AC) as first-line chemotherapy in 429 women with MBC [40]. Prior nonanthracycline-based adjuvant chemotherapy was allowed. The overall response rate and median time to disease progression were statistically superior with AD than with AC, though the median overall survival time did not differ between the two treatment arms (Table 5 A second phase III trial compared docetaxel, doxorubicin, and cyclophosphamide (TAC) at doses of 75/50/500 mg/m2, respectively, with the combination of 5-fluorouracil, doxorubicin, and cyclophosphamide (FAC, 500/50/500 mg/m2) as first-line chemotherapy for meta-static disease in 484 women [41]. Prior adjuvant chemotherapy was allowed, and patients could have received prior doxorubicin up to a cumulative dose of 240 mg/m2. While the overall response rate with TAC was significantly higher, time to disease progression and overall survival times were similar in the two treatment groups. A greater percentage of patients in the FAC group received crossover treatment with a taxane than those in the TAC group (46.2% vs. 16.5%). Both regimens were associated with a high rate of grade 34 hematologic toxicities, though neutropenia and febrile neutropenia occurred more frequently with TAC. A randomized phase II study compared AD (50/75 mg/m2) with FAC (500/50/500 mg/m2) as first-line chemotherapy in 215 MBC patients [28]. That study permitted limited prior doxorubicin exposure in the adjuvant setting. In contrast to the previous trial, significant differences in time to disease progression and overall survival time along with a superior overall response rate were seen with AD versus FAC. The absolute median survival difference was 6.5 months, representing a 40% longer survival time than in the FAC arm. The incidences of grade 34 neutropenia were similar for both arms, although febrile neutropenia occurred more frequently with AD. Among the three trials evaluating paclitaxel-based combinations, one demonstrated significantly better outcomes favoring the taxane combination. That trial compared doxorubicin and paclitaxel (50/220 mg/m2) with FAC (500/50/500 mg/m2) as first-line chemotherapy in 267 anthracycline-naïve MBC patients [29]. The overall response rate, median time to disease progression, and overall survival time were significantly better with AP than with FAC, with AP producing a median survival time that was 4 months longer. Approximately the same number of patients on the FAC and AP arms received second-line chemotherapy (44% and 48%, respectively). Paclitaxel and docetaxel were administered to 10% and 14% of patients, respectively, in the FAC group and each was administered to 1% of patients in the AP group. Grade 34 neutropenia occurred more frequently with AP, although the incidence of febrile neutropenia was low in both arms. Overall QoL measures were similar in the two treatment arms. Symptom scales of pain, fatigue, insomnia, and diarrhea favored FAC therapy, while the nausea and vomiting symptom scale favored AP therapy. In a phase III trial comparing AP (60/175 mg/m2) with AC (60/600 mg/m2) as first-line chemotherapy in 265 anthracycline-naïve patients, no differences in response or survival outcomes were seen between treatment arms [42]. A QoL analysis found no difference between treatment groups, and overall QoL was maintained. In two similar comparisons of epirubicin and paclitaxel versus epirubicin and cyclophosphamide in women with MBC, there were also no differences in either overall response rates or survival times [43, 44].
Targeted biologic therapies offer an entirely new treatment dimension for patients with MBC. The monoclonal antibody trastuzumab targets an extracellular domain of the HER-2 receptor [45]. Overexpression of HER-2 is associated with clinically aggressive disease and a shorter survival time. Synergistic activity has been observed in cellular models between trastuzumab and several chemotherapeutic agents, including docetaxel and carboplatin (Paraplatin®; Bristol-Myers Squibb), while additive activity has been observed with paclitaxel, doxorubicin, and epirubicin [45]. Clinically, trastuzumab therapy is generally well tolerated. One important caveat, however, is the potential for congestive heart failure. As the risk for congestive heart failure is much greater when trastuzumab is given with doxorubicin, this combination is generally avoided [14].
Two important phase III trials have evaluated the addition of trastuzumab to chemotherapy in women with HER-2overexpressing MBC [14, 15]. In a pivotal clinical trial reported by Slamon et al., patients received chemotherapy with either doxorubicin and cyclophosphamide (AC) or single-agent paclitaxel with or without trastuzumab. The combination of chemotherapy and trastuzumab resulted in significantly higher overall response rates with a longer median time to disease progression and overall survival time than with chemotherapy alone (Table 6
In a separate study, a QoL analysis was performed in a sample of 400 patients who received either chemotherapy with trastuzumab (n = 208) or chemotherapy alone as first-line therapy for MBC [46]. After completion of therapy, fatigue scores were significantly better than baseline scores in patients receiving chemotherapy and trastuzumab (p < .05). In addition, patients who received trastuzumab had a significant improvement in global QoL scores (p < .05).
The results of a phase III trial evaluating single-agent docetaxel (100 mg/m2) with or without trastuzumab as first-line therapy for MBC have also shown a significant benefit from the addition of trastuzumab (Table 6 Bevacizumab is a monoclonal antibody targeting vascular endothelial growth factor (VEGF). Angiogenesis is essential for cancer growth and metastasis. The consequent hyperpermeable, irregular vessels cause irregular blood flow and high interstitial fluid pressure within the tumor, which can impair the delivery of oxygen (a known radiation sensitizer) and drugs to the tumor site. Bevacizumab decreases interstitial fluid pressure in tumors, improving drug delivery and penetration [47]. Preclinical data indicate that breast cancer invasiveness and metastasis is dependent on the establishment of new blood vessels, and VEGF is a potent stimulator of angiogenesis [48].
Phase II data indicate a modest response rate of 9% for bevacizumab alone in previously treated MBC patients [49]. Building on this, a phase III trial comparing the combination of bevacizumab and capecitabine with capecitabine alone was conducted, enrolling MBC patients who had previously received both an anthracycline and a taxane (Table 6
Preliminary results from a phase III trial of paclitaxel with or without bevacizumab as first-line treatment of 715 patients with MBC appear very promising [16]. Significantly greater overall response rate and median time to disease progression were seen with the combination (Table 6
The assessment of the true survival benefits from chemotherapy in MBC can be difficult, given the potential for confounding issues, such as the impact of subsequent therapies. Nonetheless, there is an increasing number of randomized clinical trials that have documented significant survival differences. With chemotherapy regimens, the taxanes have figured prominently in those trials exhibiting a survival benefit. When present, the improvement in survival time has usually been on the order of 3 months, representing a survival time that is about 20%30% longer. It is interesting to note that, among all these trials, in no case has a docetaxel-based regimen been inferior with respect to overall survival outcome. Capecitabine and gemcitabine, two antimetabolite cytotoxic agents, have shown high activity and acceptable tolerability in a range of settings for MBC. These include single-agent and combination regimens, including inpatients with anthracycline- and/or taxane-pretreated disease. The debate concerning combination therapy versus sequential single agents continues. Combination therapies are associated with higher overall response rates, albeit at a cost of greater toxicities. And aside from the E1193 trial, well-defined comparisons of combination regimens with the same agents in sequence are not available, and the ultimate impact on survival outcomes between the two approaches remains to be seen. With targeted biologics, such as trastuzumab and bevacizumab, the potential for enhanced or synergistic activity is a compelling argument for the use of these agents in combination with traditional chemotherapeutics. In randomized studies, response and survival benefits have been impressive, with combination therapies resulting in substantially higher overall response rates. Trials with chemotherapy and trastuzumab have also demonstrated substantial improvements in overall survival ranging from 4 to 8 months, representing increases of 24% and 37% in survival time. Early data from the combination of paclitaxel and bevacizumab also appear to support a survival benefit. With respect to QoL measures, in general, treatment regimens for MBC do not appear to impair overall QoL. With trastuzumab therapy, there has even been an indication of an improvement in overall QoL following treatment. Overall, there is a growing body of phase III data on MBC that demonstrates that the introduction of modern chemotherapeutic agents, such as the taxanes, antimetabolites, and targeted biologic agents, has helped to improve survival outcomes in MBC.
Dr. OShaughnessy has acted as a consultant for Eli Lilly, Pfizer, Roche, sanofi-aventis, Abraxis, and Genentech and has received support from Roche, sanofi-aventis, Lilly, Genentech, and Abraxis.
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