Abstract
Taxanes have remained a cornerstone of breast cancer treatment over the past three decades, improving the lives of patients with both early- and late-stage disease. The purpose of this review is to summarize the current role of taxanes, including an albumin-bound formulation that enhances delivery of paclitaxel to tumors, in the management of metastatic breast cancer (MBC). Since the introduction of Cremophor EL-paclitaxel to the clinic in the mid-1990s, a substantial amount of investigation has gone into subjects such as formulation, dose, schedule, and taxane resistance, allowing physicians greater flexibility in treating patients with MBC. This review will also examine how the shrinking pool of taxane-naive patients, a result of the expansion of taxanes into the neoadjuvant and adjuvant settings, will respond to taxane retreatment for metastatic disease. Taxane treatment seems likely to continue to play an important role in the treatment of MBC.
Introduction
Apart from cancers of the skin, breast cancer is the most common cancer among women. 1 Since 1990, mortality rates for breast cancer have steadily declined. 1 However, despite significant improvements in survival, breast cancer remains second to lung cancer as one of the leading causes of cancer-related deaths among women in the United States. 1 It is estimated that 226,870 women will be diagnosed with invasive breast cancer in 2012 and that breast cancer will claim the lives of almost 40,000 women over the year. 1 Most new diagnoses of breast cancer are made at an early stage of disease; however, of those diagnosed with early breast cancer, an estimated 1 in 3 will eventually develop recurrent or metastatic disease. 2 For these women, prognosis remains poor, with median 5-year survival of <25%.1,3 Moreover, treatment-related toxicities in conjunction with common complications associated with metastatic disease, including bone fractures, liver failure, pneumonia, and respiratory failure, negatively impact the health and quality of life (QOL) of women with metastatic breast cancer (MBC).
MBC remains an incurable disease for the majority of patients. Only a select few with highly chemosensitive tumors will achieve complete response with combination chemotherapy regimens. For the remaining patients, treatment for metastatic disease is strictly palliative and is initiated with the hope of delaying disease progression, alleviating disease symptoms, improving or maintaining QOL, and potentially prolonging survival. 2 Thus, systemic chemotherapies with minimal toxicity are preferred. No single standard of care for MBC exists and treatment plans are largely individualized according to patient-(eg, age, patient preference, and QOL considerations) and tumor-specific factors. Treatment selection for MBC is highly influenced by hormone receptor (HR; composed of estrogen receptor and progesterone receptor) status and human epidermal growth factor receptor 2 (HER2) status of the tumor. 4 Current guidelines recommend systemic chemotherapy for women with HR-negative disease that is not localized to bone or soft tissue and is associated with symptomatic visceral disease or for women with HR-positive disease that has demonstrated resistance to endocrine therapy. 4 Single agents including taxanes, anthracyclines, antimetabolites, and vinca alkaloids or combinations of these agents have demonstrated clinically meaningful benefit in such women with HR-negative MBC. For women with HER2-positive disease, trastuzumab in combination with a taxane, vinorelbine, or capecitabine are the preferred treatment regimens. 4
Taxane-based regimens are among the most effective and commonly used systemic therapies for breast cancer, particularly in the adjuvant setting. Accordingly, the role of taxanes in the metastatic setting continues to evolve as clinicians seek new strategies to optimize outcomes of their patients. This review describes the evolution of taxane therapy for MBC including the development of the novel delivery platform of nanoparticle albumin-bound (
Historical Overview of Taxanes for the Treatment of Breast Cancer
The introduction of taxanes in the mid-1990s marked a significant advance in the treatment of MBC. In clinical trials, these potent antitumor agents provided improved outcomes for patients with both early and advanced disease.5,6 The antitumor activity of paclitaxel, isolated from extracts from Pacific yew trees (
Docetaxel, a more potent semisynthetic derivative of paclitaxel, derived from extracts from the needles of the European yew tree (
Cremophor EL (CrEL-) paclitaxel (Taxol), initially approved for the treatment of relapsed ovarian cancer, received US Food and Drug Administration (FDA) approval in 1994 for the treatment of patients with MBC who did not respond to anthracycline-based combination chemotherapy or with breast cancer that recurred within 6 months of adjuvant chemotherapy.7,13–15 Approval was based on a phase III trial of 2 different doses (175 or 135 mg/m2) of CrEL-paclitaxel given every 3 weeks (q3w) in patients with MBC who had failed to respond to previous chemotherapy. The higher dose (175 mg/m2) vs. the lower dose (135 mg/m2) of CrEL-paclitaxel was associated with a longer median time to disease progression (4.2 vs. 3.0 months, respectively;
Docetaxel (Taxotere) received FDA approval in 1996 for locally advanced or metastatic breast cancer after failure of prior chemotherapy, marking a second important milestone in the treatment of MBC.10,18 In a phase III trial in patients with MBC whose disease had progressed despite previous anthracycline-containing therapy, single-agent docetaxel 100 mg/m2 q3w was superior to mitomycin 12 mg/m2 dose every 6 weeks plus vinblastine 6 mg/m2 q3w in terms of overall response rate (ORR; 30.0% vs. 11.6%;
The promising activity of docetaxel as a single-agent therapy spurred direct comparison of docetaxel and CrEL-paclitaxel in the treatment of MBC. In a phase III randomized trial comparing CrEL-paclitaxel 175 mg/m2 given by 3-hour infusion q3w and docetaxel 100 mg/m2 given by 1-hour infusion q3w in patients with MBC whose disease had progressed during or within 12 months of receiving anthracycline-containing chemotherapy, docetaxel was superior to CrEL-paclitaxel in terms of OS (15.4 vs. 12.7 months, respectively;
Efficacy in head-to-head trials of taxanes.
Safety in head-to-head trials of taxanes (grade 3/4 adverse events).
Role of nab-Paclitaxel in the Management of MBC
Both CrEL-paclitaxel and docetaxel have demonstrated significant clinical efficacy in MBC; however, both agents are associated with characteristic toxicities, mainly hypersensitivity reactions and peripheral neuropathy at least partially due to their respective solvents–-CrEL and polysorbate 80.10,13,20 Efforts to improve on the tolerability of the solvent-based taxanes using a novel method for drug delivery led to the development of
The ORR was also significantly higher in patients who received
The proposed mechanism of drug delivery of
SPARC is overexpressed in many tumors, especially in cells associated with the tumor stroma and vasculature, and may play a role in cancer progression and metastasis.
30
SPARC appears to be more highly expressed in breast tumors relative to normal tissue,
31
and Jones et al
32
found that high levels of SPARC transcription in tumor samples were significantly associated with a shorter OS of patients with breast cancer. More recently, it has been shown that SPARC expression positively correlates with treatment response to
Optimizing Taxane Therapy
Combination therapies with taxanes
A number of combination therapies have been studied for the treatment of MBC, and several taxane combinations are highlighted by the National Comprehensive Cancer Network (NCCN) as preferred regimens, including doxorubicin with docetaxel or CrEL-paclitaxel, capecitabine with docetaxel, and gemcitabine with CrEL-paclitaxel. 4 The NCCN guidelines go on to state that although combination chemotherapy often produces higher response rates and longer disease-free intervals in comparison with single agents, these regimens are associated with increased toxicity and do not lead to significant improvements in OS. Administering single agents sequentially reduces the likelihood for dose reductions. Thus, the NCCN panel states that there is “little compelling evidence that combination chemotherapy is superior to sequential single agents.” 4
Schedule: CrEL-paclitaxel and docetaxel
Single-agent CrEL-paclitaxel administered q3w36,37 or weekly
38
is active as initial or subsequent therapy for MBC. Similarly, docetaxel is active in anthracycline-resistant and/or pretreated patients with MBC when administered q3w or weekly.39–41 A phase III study showed efficacy benefits of a weekly (n = 346) vs. q3w (n = 383) schedule of CrEL-paclitaxel in terms of ORR (42% vs. 29%, respectively;
Docetaxel, on the other hand, may exhibit greater clinical efficacy on a q3w schedule for patients with MBC (Table 3). A phase III study comparing a q3w schedule vs. a first-3-of-4-weeks (qw 3/4) schedule (n = 59 for each) for docetaxel demonstrated a higher ORR (35.6% vs. 20.3%, respectively) and similar progression-free survival (PFS; 5.7 vs. 5.5 months;
Dose optimization for the taxanes: efficacy.
Schedule: nab-paclitaxel
Early dosing regimens of
The influence of schedule on clinical outcomes in patients receiving taxanes and the feasibility of dosing
Breast Cancer Subtypes
Histologic subtypes
In the era of personalized medicine, it is prudent to consider how taxanes are used to treat different subtypes of breast cancer. Histological subtypes of breast cancer are defined by tumor expression of estrogen receptor (ER), progesterone receptor (PR), and HER2.
4
Physicians now have the ability to tailor treatment based on the expression of these molecules. Guidelines defined by the NCCN recommend that patients with ER/PR+ metastatic disease receive first-line endocrine therapy.
4
On the other hand, patients whose tumors are negative for hormone receptor expression should consider chemotherapy. Among the options for ER/PR– disease are single-agent therapy or combination therapy. CrEL-paclitaxel, docetaxel, and
BRCA1 and BRCA2
The breast cancer genes 1 and 2 (BRCA1 and BRCA2) are known to play important roles in DNA repair,50,51 and mutation of these genes is known to associate with breast cancer.
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The utility of taxane treatment for patients with mutations in BRCA1 and BRCA2 vs. patients with “sporadic” breast cancer has been examined in the metastatic setting.
53
In this trial, the majority of patients received docetaxel (83%), and the most treatment took place in either the second- or third-line setting (84%). Interestingly, it appeared that patients with BRCA1 mutations demonstrated lower response rates (23% vs. 38%,
Genetic Markers for Taxane Treatment
Genetic markers that predict response, resistance, or toxicity are a promising avenue by which to identify patients most appropriate for treatment with taxanes. Several studies have focused on identifying mechanisms that underlie resistance to taxane treatment. Mutations in or differential expression of β-tubulin and the multidrug resistance 1 (
CrEL-Paclitaxel and Docetaxel in Early Breast Cancer
The management of breast cancer continues to evolve with the introduction of new, more effective agents and the expanding role of taxanes in early breast cancer treatment.
6
In 1999, CrEL-paclitaxel administered sequentially with standard doxorubicin-containing combination therapy was approved as adjuvant treatment for patients with node-positive breast cancer.13,14 Subsequently in 2004, a similar indication was added for docetaxel in the adjuvant setting with an approval in combination with doxorubicin and cyclophosphamide for patients with node-positive resectable breast cancer.10,18 A Cochrane meta-analysis reported a positive benefit in a combined analysis of both taxanes in the adjuvant treatment of breast cancer in terms of OS (hazard ratio, 0.81; 95% CI, 0.75–0.88;
One of the first trials to demonstrate the benefit of a taxane in the neoadjuvant setting was a trial of 162 women with locally advanced breast cancer who were treated with doxorubicin/cyclophosphamide plus vincristine and prednisolone as induction chemotherapy.
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Patients who responded to induction therapy were then randomized to continue the induction chemotherapy regimen or switch to docetaxel. Responding patients who switched to docetaxel achieved a significantly higher pathologic complete response compared with those who did not (34% vs. 16%;
Impact of Early Taxane Use on Decision Making by Physicians for Treating MBC
Treatments for taxane- or anthracycline-treated MBC
Resistance to chemotherapy accounts for >90% of treatment failures in patients with metastatic cancer.65,66 As a result, treatment options have become limited for these patients with MBC and prior exposure to chemotherapy. Until recently, capecitabine was the only approved agent for the treatment of patients with anthracycline- or taxane-resistant MBC.67,68 Numerous trials have shown response rates of 15% to 40% in patients receiving capecitabine after exhibiting resistance to anthracycline- or taxane-based therapy. In these trials, the median TTPs were 3 to 6 months.69–72 Recently, two additional agents were approved by the FDA for the treatment of anthracycline- or taxane-resistant MBC: ixabepilone with or without capecitabine and eribulin mesylate.68,73,74 Other drugs used in this setting include
Retreatment with taxanes
More patients with breast cancer are receiving anthracycline- or taxane-containing regimens in the adjuvant setting, which has resulted in a higher number of patients with resistant or refractory disease in the metastatic setting.49,64,66 Several studies have looked at retreatment with a taxane for metastatic disease after failure of prior taxane therapy. In two small retrospective studies, patients had received CrEL-patients had received prior CrEL-paclitaxel or docetaxel, respectively.75,76 In both studies, partial cross-resistance between CrEL-paclitaxel and docetaxel was observed. Retreatment of 24 patients with docetaxel 75 mg/m2 q3w after failure of CrEL-paclitaxel treatment led to an ORR of 25%. 75 A similar ORR of 32% was observed in 44 patients retreated with CrEL-paclitaxel 80 mg/m2 weekly after prior exposure to docetaxel (42 patients had also received prior anthracycline therapy). 76 Response lasted a median of 6 months, and median TTP was 5 months. Among the 14 responders to taxane retreatment with CrEL-paclitaxel, half had documented primary resistance to docetaxel therapy, which was defined as disease progression during docetaxel treatment or within 12 months of completing docetaxel treatment. In this trial, the most common grade 3/4 adverse events were neutropenia (27%), leukopenia (25%), and sensory neuropathy (14%).
Prospective studies of taxane retreatment documented similar findings. In a phase II trial of CrEL-paclitaxel 80 mg/m2 given weekly to previously treated patients with MBC (n = 212), 25% (54 patients) had received prior taxane therapy (38 CrEL-paclitaxel, 15 docetaxel, and 1 patient had received both). 38 Prior taxane therapy was primarily given in the metastatic setting (49 patients), whereas 5 patients had received adjuvant CrEL-paclitaxel. The median duration from prior taxane therapy to retreatment with CrEL-paclitaxel was 83 days, and 28 patients had previously been exposed to a taxane within 3 months of retreatment. Among the 45 evaluable patients who had received prior taxane therapy, 7 patients (15.6%) had a response to CrEL-paclitaxel retreatment. In a separate phase II trial, retreatment of CrEL-paclitaxel-resistant patients with MBC (n = 44 evaluable patients) with docetaxel 100 mg/m2 q3w led to an ORR of 18.1% (1 complete and 7 partial). 77 Duration of response lasted 29 weeks, and median TTP was 10 weeks. An interesting finding from this study was that it appeared that the length of CrEL-paclitaxel infusion correlated with the response to retreatment with docetaxel. None of the 12 patients who received CrEL-paclitaxel over a 24-hour infusion responded to retreatment with docetaxel, whereas 25% of the 32 patients receiving short infusions of CrEL-paclitaxel (1- or 3-hour infusion) achieved an objective response. The most common severe adverse events were febrile neutropenia (24%), asthenia (22%), and infection (13%). Grade 3 sensory neuropathy occurred in 7% of patients. Taken together, the results from these trials demonstrate that 20% to 30% of patients who failed a prior taxane-containing regimen may still be able to achieve a response with taxane retreatment.
Many of the studies described above defined patients with prior exposure to a taxane in the metastatic setting and not exclusively the neoadjuvant or adjuvant setting. A recent study out of Germany called the Taxane Re-Challenge Cohort Study retrospectively identified 381 patients with recurrent disease who were treated in the neoadjuvant or adjuvant setting with a taxane-based regimen.
78
Data were collected on their subsequent treatment. A total of 106 patients (27.8%) were retreated with a taxane-containing regimen as first-line or later-line therapy for recurrent disease. A response rate of 48.6% was observed for 74 patients who received first-line taxane-based therapy for recurrent disease; 27% had complete response. The ORR for later-line therapy was 28.2%. Response to taxane retreatment was dependent on the disease-free interval. If patients had disease recurrence within 1 year, response rates were 34.8%; 1 to 2 years, 42.9%; and >2 years, 63.3% (
Physicians must base the decision to treat patients with taxane-refractory disease by rechallenge with a taxane vs. a switch to a different agent on a number of factors. If taxane rechallenge is desirable, the oncologist must consider the dosing schedule of previous taxane regimens. Another important consideration is the length of time that has passed from the completion of previous taxane therapy (adjuvant or metastatic). Patients with disease recurrence several years after taxane therapy can receive taxane therapy again. For treatment very soon after the failure of a taxane, a different regimen, such as single-agent capecitabine, eribulin mesylate, or ixabepilone, may be considered.4,66 Additionally, the combination of ixabepilone plus capecitabine demonstrated a longer PFS vs. capecitabine alone in women with MBC that had progressed during anthracycline and taxane treatment (5.8 vs. 4.2 months; hazard ratio = 0.75;
nab-Paclitaxel for taxane-exposed patients
Taxane formulation may also play a key role in determining whether previously taxane-exposed patients will respond to taxane rechallenge. Specifically, there is evidence that patients who have previously received solvent-based taxanes may benefit from treatment with
The response rates in taxane-exposed patients in the Blum et al study described above agree with those of a study presented at the annual meeting of the American Society of Clinical Oncology in 2011 on the repeat use of taxanes for MBC.
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That study reported a response rate of 14.7% in patients (n = 34) receiving
Although the studies above describe clinical outcomes in patients who had received taxanes as a previous course of therapy for MBC, it is also important to establish the role of
Conclusions
As discussed throughout this review, the taxanes remain a key component of MBC treatment. Data presented here demonstrate the gains in efficacy that have been seen with the evolution of taxane treatment from the development of CrEL-paclitaxel beginning in the 1960s through the ongoing investigation of
Resistance to taxane treatment has spurred investigation of numerous combination therapies. Although many taxane-containing combination therapies are recognized as possessing benefits in terms of response rates and PFS, NCCN guidelines point to the lack of OS benefit and increased toxicities that combination therapies have demonstrated as disadvantages to combination therapy. 4 However, sequential systemic therapies do not appear to suffer from these same drawbacks.
The development of
Author Contributions
Conceived and designed the experiments: WJG. Analysed the data: WJG. Wrote the first draft of the manuscript: WJG. Contributed to the writing of the manuscript: WJG. Agree with manuscript results and conclusions: WJG. Jointly developed the structure and arguments for the paper: WJG. Made critical revisions and approved final version: WJG. The author reviewed and approved of the final manuscript.
Funding
This work was funded by Celgene Corporation.
Competing Interests
Author(s) disclose no potential conflicts of interest.
Disclosures and Ethics
As a requirement of publication author(s) have provided to the publisher signed confirmation of compliance with legal and ethical obligations including but not limited to the following: authorship and contributorship, conflicts of interest, privacy and confidentiality and (where applicable) protection of human and animal research subjects. The authors have read and confirmed their agreement with the ICMJE authorship and conflict of interest criteria. The authors have also confirmed that this article is unique and not under consideration or published in any other publication, and that they have permission from rights holders to reproduce any copyrighted material. Any disclosures are made in this section. The external blind peer reviewers report no conflicts of interest. Provenance: the authors were invited to submit this paper.
Footnotes
Acknowledgments
The author received editorial support in preparation of this manuscript from John McGuire, PhD, of MediTech Media, Ltd. The author was fully responsible for content and editorial decisions for this manuscript.
