Systematic review of ixabepilone for treating metastatic breast cancer

BACKGROUND

Ixabepilone is now a Food and Drug Administration-approved therapeutic option for patients with metastatic breast cancer (MBC) whose disease has progressed despite prior anthracycline and taxane therapy. We conducted a systematic review and meta-analysis to systematically evaluate the efficacy and safety of ixabepilone for treating metastatic breast cancer.

METHODS

A systematic review and meta-analysis were conducted. Randomized controlled studies applying ixabepilone for treating MBC were included. The primary outcome was Overall Survival (OS). The authors of primary articles were contacted and methodological quality was evaluated. Subgroups were drawn based on intervention measures; heterogeneity and bias were discussed.

RESULTS

Eight studies with 5247 patients were included. Compared with a weekly schedule, a triweekly schedule of ixabepilone was better at improving overall response rate (ORR), while there were no differences in improving OS and progression-free survival (PFS). Ixabepilone plus capecitabine was superior to capecitabine monotherapy in improving OS, PFS and ORR. Paclitaxel was more effective than ixabepilone in terms of OS and PFS. There was no difference in the improvement of ORR, clinical benefit rate (CBR) and disease control rate (DCR) between ixabepilone and eribulin.

CONCLUSIONS

Current evidence suggests that a triweekly schedule of ixabepilone is more effective than weekly dosing in improving ORR. Use of ixabepilone in combination with capecitabine possesses superior clinical efficacy to the use of capecitabine alone. Paclitaxel was more effective than ixabepilone in terms of OS and PFS. The efficacy and safety between ixabepilone and eribulin were identical.

Taxane-containing regimens for metastatic breast cancer

BACKGROUND

It is generally accepted that taxanes are among the most active chemotherapy agents in the management of metastatic breast cancer. This is an update of a Cochrane review first published in 2003.

OBJECTIVES

The objective of this review was to compare taxane-containing chemotherapy regimens with regimens not containing a taxane in the management of women with metastatic breast cancer.

SEARCH METHODS

In this review update, we searched the Cochrane Breast Cancer Group Specialised Register, MEDLINE, EMBASE, the World Health Organization's International Clinical Trials Registry Platform (WHO ICTRP), and ClinicalTrials.gov on 14 February 2013 using keywords such as 'advanced breast cancer' and 'chemotherapy'. We searched reference lists of articles, contacted study authors, and did not apply any language restrictions.

SELECTION CRITERIA

Randomised controlled trials comparing taxane-containing chemotherapy regimens to regimens without taxanes in women with metastatic breast cancer. We included published and unpublished studies.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We derived hazard ratios (HRs) for overall survival, time to progression, and time to treatment failure where possible, and used a fixed-effect model for meta-analysis. We represented objective tumour response rates and toxicity as risk ratios (RRs). We extracted quality of life data where present.

MAIN RESULTS

This review included 28 studies. The updated analysis included 6871 randomised women, while the original review had 3643 women. Of the 28 included studies, we considered 19 studies to be at low risk of bias overall; however, some studies failed to report details on allocation concealment and methods of outcome assessment for those outcomes that are more likely to be influenced by a lack of blinding (for example tumour response rate). Studies varied in the taxane-containing chemotherapy backbone, and the comparator arms and were categorised into three groups: Regimen A plus taxane versus Regimen A (2 studies); Regimen A plus taxane versus Regimen B (14 studies); and single-agent taxane versus Regimen C (13 studies). Thirteen studies used paclitaxel, 14 studies used docetaxel, and 1 study allowed the investigator to decide on the type of taxane; the majority of studies delivered a taxane every 3 weeks. Twenty studies administered taxanes as first-line treatment, and 21 studies involved anthracycline naïve women in the metastatic setting. The combined HR for overall survival and time to progression favoured the taxane-containing regimens (HR 0.93, 95% confidence interval (CI) 0.88 to 0.99, P = 0.002, deaths = 4477; and HR 0.92, 95% CI 0.87 to 0.97, P = 0.002, estimated 5122 events, respectively) with moderate to substantial heterogeneity across trials. If the analyses were restricted to studies of first-line chemotherapy, this effect persisted for overall survival (HR 0.93, 95% CI 0.87 to 0.99, P = 0.03) but not for time to progression (HR 0.96, 95% CI 0.90 to 1.02, P = 0.22). Tumour response rates appeared to be better with taxane-containing chemotherapy in assessable women (RR 1.20, 95% CI 1.14 to 1.27, P < 0.00001) with substantial heterogeneity across studies. Taxanes were associated with an increased risk of neurotoxicity (RR 4.84, 95% CI 3.18 to 7.35, P < 0.00001, 24 studies) and hair loss (RR 2.37, 95% CI 1.45 to 3.87, P = 0.0006, 11 studies) but less nausea/vomiting compared to non-taxane-containing regimens (RR 0.62, 95% CI 0.46 to 0.83, P = 0.001, 26 studies). Leukopaenia and treatment-related death did not differ between the two groups (RR 1.07, 95% CI 0.97 to 1.17, P = 0.16, 28 studies; and RR 1.00, 95% CI 0.63 to 1.57, P = 0.99, 23 studies, respectively). For quality of life measures, none of the individual studies reported a difference in overall or any of quality of life subscales between taxane-containing and non-taxane chemotherapy regimens.

AUTHORS' CONCLUSIONS

Taxane-containing regimens appear to improve overall survival, time to progression, and tumour response rate in women with metastatic breast cancer. Taxanes are also associated with an increased risk of neurotoxicity but less nausea and vomiting compared to non-taxane-containing regimens. The considerable heterogeneity encountered across studies probably reflects the varying efficacy of the comparator regimens used in these studies and indicates that taxane-containing regimens are more effective than some, but not all, non-taxane-containing regimens.

Phase II randomized trial of weekly and every-3-week ixabepilone in metastatic breast cancer patients

This multicenter, open-label, randomized phase II trial compared the efficacy and tolerability of weekly ixabepilone versus the standard 3 weekly dosing regimen. Patients with human epidermal growth factor receptor 2-negative, metastatic breast cancer (MBC) were randomly assigned to receive either ixabepilone 16 mg/m(2) as a 1-h intravenous (IV) infusion weekly on days 1, 8, and 15 of a 28-day cycle (1 week off therapy; n = 85), or 40 mg/m(2) as a 3-h IV infusion on day 1 of a 21-day cycle (n = 91), until disease progression or unacceptable toxicity. Randomization was stratified by (i) measurable versus nonmeasurable (evaluable) disease, (ii) ≤two versus >two prior chemotherapy regimens for MBC, and (iii) hormone receptor (HR)-positive versus HR-negative breast cancer. The primary endpoint was rate of progression-free survival (PFS) at 6 months. Of 176 randomized patients, 171 were treated. The 6-month PFS rate was significantly higher in patients treated with ixabepilone every 3 weeks (42.7, 95 % confidence interval [CI] 31.5-53.5) compared with those who received ixabepilone weekly (28.6, 95 % CI 18.9-38.9; log-rank P = 0.03). Every-3-week dosing significantly prolonged median PFS versus weekly dosing (5.3 vs. 2.9 months; log-rank P = 0.05). The every-3-week regimen was associated with higher rates of grade 3/4 toxicities, particularly neutropenia (38.2 vs. 6.1 %) and a higher rate of patient withdrawal due to adverse events. These results suggest that every-3-week ixabepilone is more effective than weekly treatment in MBC, albeit with more toxicity.

Biomarker analysis of neoadjuvant doxorubicin/cyclophosphamide followed by ixabepilone or Paclitaxel in early-stage breast cancer

PURPOSE

Predictive biomarkers offer the potential to improve the benefit:risk ratio of a therapeutic agent. Ixabepilone achieves comparable pathologic complete response (pCR) rates to other active drugs in the neoadjuvant setting. This phase II trial was designed to investigate potential biomarkers that differentiate response to this agent.

EXPERIMENTAL DESIGN

Women with untreated, histologically confirmed primary invasive breast adenocarcinoma received neoadjuvant doxorubicin/cyclophosphamide, followed by 1:1 randomization to ixabepilone (n = 148) or paclitaxel (n = 147). Rates of pCR were compared between treatment arms based on predefined biomarker sets: TUBB3, TACC3, and CAPG gene expression, a 20- and 26-gene expression model, MDR1 protein expression, and other potential markers of sensitivity. βIII-tubulin protein expression is reported separately but is referred to here for completeness. All patients underwent a core needle biopsy of the primary cancer for molecular marker analysis before chemotherapy. Gene expression profiling data were used for molecular subtyping.

RESULTS

There was no significant difference in the rate of pCR in both treatment arms in βIII-tubulin-positive patients. Higher pCR rates were observed among βIII-tubulin-positive patients than in βIII-tubulin-negative patients. Furthermore, no correlation was evident between TUBB3, TACC3, and CAPG gene expression, MDR1 protein expression, multi-gene expression models, and the efficacy of ixabepilone or paclitaxel, even within the estrogen receptor-negative subset.

CONCLUSION

These results indicate that βIII-tubulin protein and mRNA expression, MDR1 protein expression, TACC3 and CAPG gene expression, and multigene expression models (20- and 26-gene) are not predictive markers for differentiating treatment benefit between ixabepilone and paclitaxel in early-stage breast cancer.

Beyond taxanes: the next generation of microtubule-targeting agents

Taxanes are a standard first-line option for metastatic breast cancer (MBC), but their utility may be limited by primary or acquired resistance. New microtubule-targeting agents have been developed to overcome taxane resistance and provide additional options for improving patient outcomes. This article reviews these alternative microtubule-targeting agents and their potential clinical benefits for MBC patients. Relevant clinical data were compiled through searches within PubMed and congress abstract databases. Ixabepilone, a novel microtubule-stabilizing drug approved by the US Food and Drug Administration (FDA), has proven efficacy across multiple lines of therapy, including patients with taxane-resistant/refractory disease. In phase III trials, ixabepilone plus capecitabine significantly improved progression-free survival compared with capecitabine alone in anthracycline/taxane-pretreated patients. Eribulin has recently been approved by the FDA and by the European Medicines Agency for the treatment of patients with MBC who have received at least two prior chemotherapy regimens for late-stage disease. In a phase III trial, eribulin extended overall survival compared with the physician’s treatment choice in heavily pretreated MBC patients. In addition, several investigational microtubule-targeting agents may have therapeutic potential in MBC. The development of new microtubule-targeting agents helps to address the need for additional effective regimens for patients progressing after standard treatment with anthracycline- and taxane-containing regimens.

Global experience with ixabepilone in breast cancer

Ixabepilone approval in a number of countries across the world as monotherapy and in combination with capecitabine has led to widespread uptake in the later-line breast cancer setting. However, individualized data for ixabepilone in different ethnic groups are limited. Overall, data from small numbers of ethnic subgroups including Hispanic, Japanese and Chinese patients have revealed no clinically significant variation in the disposition, efficacy or tolerability of ixabepilone from that established in pivotal trials. Global use of ixabepilone, while usually along the lines of standard practice, may vary because of local regulatory decisions, clinical practice guidelines and cost considerations. Further information on the global patterns of use of ixabepilone will assist in optimizing the use of this novel therapy.

Synergistic activity of ixabepilone plus other anticancer agents: preclinical and clinical evidence

Ixabepilone demonstrates marked synergistic activity in combination with capecitabine, which served as the rationale for the evaluation of this combination in the clinic. Ixabepilone plus capecitabine is currently approved for patients with locally advanced or metastatic breast cancer (MBC) progressing after treatment with an anthracycline and a taxane; approval was based on the results of two phase III trials comparing the combination with capecitabine monotherapy. An array of preclinical studies in multiple solid tumor types show that ixabepilone demonstrates therapeutic synergy with targeted therapies including trastuzumab, bevacizumab, brivanib, and cetuximab; with immune-modulating agents such as anti-CTLA-4 antibody; and with other chemotherapy drugs such as irinotecan and epirubicin. Notably, experiments in several xenograft models show that ixabepilone provides greater antitumor synergism when combined with bevacizumab than either paclitaxel or nab-paclitaxel combined with bevacizumab. These preclinical findings provide a foundation for ongoing phase II clinical trials using ixabepilone in combination with trastuzumab or lapatinib in HER2-positive breast cancer; with bevacizumab in breast cancer, endometrial cancer, renal cancer, and non-small cell lung cancer (NSCLC); with cetuximab in breast cancer, NSCLC, and pancreatic cancer; and with brivanib, dasatinib, sorafinib, sunitinib, or vorinostat in MBC. Preliminary results from several of these trials suggest that ixabepilone-based combinations have promising anticancer activity.

Weekly ixabepilone administration in heavily pretreated metastatic breast cancer patients

Ixabepilone 40 mg/m(2) administered on an every 3-week schedule is approved for use in metastatic breast cancer (MBC) as monotherapy, or in combination with capecitabine in anthracycline/taxane resistant tumors. Because the mechanism of action and toxicity profile is similar to the taxanes, it has been suggested that weekly administration (15-20 mg/m(2) on days 1, 8, 15 for 28 days/cycle) may provide a therapeutic advantage while minimizing toxicity. We report 24 MBC patients treated with weekly ixabepilone. Demographics, ER/PR/HER-2/neu, ECOG performance status (PS), sites of metastatic disease, lines of previous therapy, dosage, treatment duration, dose reductions/interruptions, hematologic/non-hematologic toxicities, growth factor use, reasons for discontinuation, time to progression (TTP), and response rate were recorded. Median age was 61 years (33-79). 0-1 ECOG PS was 54%. Sixty-seven percent of patients received ≥ 4 previous chemotherapy regimens. Median treatment duration was 1.4 months (0.5-10.8). Median dose was 16 mg/m(2) (15-20). In 37.5% of patients, the dose was held due to toxicities with median missed dose of 2. Partial response and stable disease were 4 and 48%. Median TTP was 2.1 months (0.9-16.4). Majority of patients discontinued therapy due to disease progression (84%). Grade 3-4 neutropenia and neuropathy were 4% and 8%. It is not yet clear whether the weekly administration of ixabepilone impacts the risk/benefit profile. There are clinical data to suggest that weekly ixabepilone is efficacious and tolerable. Upcoming clinical trials will continue to inform the question. Our data suggest that weekly ixabepilone is well tolerated with a manageable side-effect profile in this small, heavily pretreated population.