Efficacy and acceptability of neoadjuvant endocrine therapy in patients with hormone receptor‐positive breast cancer: A network meta‐analysis

Abstract

Background

The optimal sequence of endocrine therapy in a neoadjuvant setting for hormone receptor‐positive (HR+) breast cancer is unclear. Our study evaluated the efficacy and acceptability of neoadjuvant endocrine therapy for HR+ breast cancer.

Methods

We identified studies based on titles and abstracts that were published before 22 June 2018 in the following databases: PubMed, EMBASE, and the Cochrane Library. Eligible studies were randomised controlled trials with at least one arm that evaluated the effectiveness of one or a combination of anastrozole, letrozole, palbociclib, tamoxifen, fulvestrant, abemaciclib, everolimus, gefitinib, ribociclib, taselisib, and exemestane. We pooled effect sizes using the odds ratio (OR) and corresponding 95% credibility interval (95% CrI). The primary outcomes were response rate and treatment completion.

Results

Our network meta‐analysis included 3,306 participants and 16 eligible studies, which assessed 15 treatments. In terms of response rates, compared with letrozole combined therapy, tamoxifen was associated with a significant reduction in response rate (OR, 0.34; 95% CrI, 0.13–0.85; OR, 0.32; 95% CrI, 0.13–0.80; OR, 0.26; 95% CrI, 0.09–0.83; and OR, 0.30; 95% CrI, 0.09–0.96; for letrozole plus everolimus, letrozole plus taselisib, letrozole plus zoledronic acid, and letrozole plus lapatinib, respectively). Based on the surface under the cumulative ranking curves ranking, letrozole plus zoledronic acid was associated with the highest rate of response (87.6%), followed by letrozole plus lapatinib (85.2%), and letrozole plus taselisib (79.3%).

Conclusions

Ultimately, our study established that letrozole plus zoledronic acid may be an optimal treatment based on its current rank in a neoadjuvant setting for HR+ breast cancer.

Neoadjuvant therapy enhance the rate of success for breast conservation surgery. Neoadjuvant endocrine therapy (NET) is effective for hormone receptor‐positive breast cancer. The optimal sequence of NET is not clear. Letrozole plus zoledronic acid may be the optimal treatment in terms of response rate.

1. INTRODUCTION

Among women, breast cancer is one of the most commonly diagnosed malignant diseases and the main cause of cancer‐related deaths worldwide (Torre et al., 2015). The main treatment strategies for breast cancer are surgery, radiotherapy, chemotherapy, endocrine therapy, and targeted therapy, which could each improve the survival rate in breast cancer. Neoadjuvant chemotherapy (NCT), as the standard of care in preoperative systemic therapy for breast cancer, has achieved robust clinical efficacy. The clinical advantages of neoadjuvant therapy are known to include a reduction in tumour volume, which can both make breast cancer patients candidates for breast conservation surgery (BCS) rather than mastectomy and enhance the rate of success for BCS (Mauriac et al., 1999; Rastogi et al., 2008). Nevertheless, for hormone‐sensitive breast cancer patients or patients who cannot tolerate chemotherapy, it is difficult to obtain a pathologic complete response using NCT (H. D. Bear et al., 2003; H. Bear et al., 2006; Toi et al., 2008). Moreover, a previous systemic review and meta‐analysis demonstrated that neoadjuvant endocrine therapy (NET) yielded a similar response rate as NCT, but with less toxicity (Spring et al., 2016). Therefore, especially for hormone‐sensitive, postmenopausal women with breast cancer, NET is likely to be more suitable than NCT (Dixon et al., 2000; Reinert, Gonçalves, & Ellis, 2018).

Currently, the most commonly used endocrine therapy includes the following types of drugs: selective oestrogen receptor modulators, an aromatase inhibitor (AI), and selective oestrogen receptor downregulators. Although endocrine therapy primarily has been used in adjuvant settings, it is also effective in a neoadjuvant setting. Since the introduction of third‐generation AI, several studies have been conducted to investigate the effectiveness of NET against hormone receptor‐positive (HR+) breast cancer. For example, for both the objective response rate and BCS, letrozole is superior to tamoxifen as neoadjuvant therapy in postmenopausal patients with hormone‐sensitive breast cancer and is associated with less toxicity based on data from the P024 trial (Eiermann et al., 2001). A phase 2 clinical trial of anastrozole versus fulvestrant as preoperative treatment in postmenopausal women with HR+ breast cancer demonstrated that fulvestrant is as effective as anastrozole and is well tolerated (Lerebours et al., 2016). Moreover, clinical evidence favouring the combination of everolimus and letrozole rather than letrozole alone was established in a phase 2 trial in oestrogen receptor‐positive (ER+) breast cancer. In that study, response rates by clinical palpation were 68.1% in the letrozole plus everolimus group, compared with 59.1% in the letrozole alone group (Baselga et al., 2009).

Although a previous network meta‐analysis of NET was conducted (Wang et al., 2012), currently there are many neoadjuvant trials testing new drugs, such as taselisib or palbociclib combined with letrozole in patients with ER+ breast cancer (ClinicalTrials.gov, 2018; Saura et al., 2017). This increase in choices for neoadjuvant endocrine agents prompted us to define the optimal neoadjuvant therapy for hormone‐sensitive breast cancer. Therefore, to effectively guide the clinical application of these agents, we adopted a network meta‐analysis to combine direct and indirect evidence according to new clinical data and to further verify the effectiveness and acceptability of NET.

2. MATERIALS AND METHODS

2.1. Literature search

For studies published before 22 June 2018, we identified studies of interest by first performing an electronic literature search based on titles and abstracts of the following databases: PubMed, EMBASE, and the Cochrane Library. No restrictions were made for language or year of publication. Grey literatures were not included. For database searches, the following primary keywords were used: breast neoplasms, anastrozole, letrozole, palbociclib, tamoxifen, fulvestrant, abemaciclib, everolimus, gefitinib, ribociclib, taselisib, exemestane, and randomised controlled trials. The search strategy was designed and developed by JH Tian (>10 years' experience as information specialist). Moreover, additional relevant references were manually identified by tracking eligible trials that cited the articles that we included and through related systematic reviews and meta‐analyses. The detailed search strategies of the different databases are shown in Supporting Information Tables S1–S3.

We performed a network meta‐analysis based on the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta‐Analysis (PRISRM) extension for network meta‐analysis (Hutton et al., 2015).

2.2. Inclusion and exclusion criteria

Inclusion and exclusion criteria were generated based on the framework of the population‐intervention‐comparator‐outcomes‐study design (PICOS; Costantino, Montano, & Casazza, 2015). The included population was female postmenopausal HR+ breast cancer patients; other tumours were excluded, such as unresectable or metastatic breast cancer. Eligible studies were randomised, controlled, neoadjuvant clinical trials that had at least one arm that evaluated the effectiveness of one or a combination of anastrozole, letrozole, palbociclib, tamoxifen, fulvestrant, abemaciclib, everolimus, gefitinib, ribociclib, taselisib, or exemestane. The primary outcome was the response rate. The secondary outcome was treatment completion. Studies that did not have a valid outcome indicator for consolidation were excluded. If more than one publication of the same trial was retrieved, only the most comprehensive and/or informative publication was included. In addition, our network meta‐analysis represents a combined analysis of the available literature, and each article provides a detailed description of its consent process; therefore, institutional review board approval was not required for this meta‐analysis.

2.3. Data extraction and quality assessment

Two authors (T. T. Z. and Y. Y.) independently extracted data and performed quality assessments; if there was a disagreement, it was resolved by consensus, while a third author (F. B. F.) provided arbitration when necessary. Data were extracted using a predefined spreadsheet based on intent‐to‐treat analysis, including the following data: first author's name, publication date, national clinical trial, funding, journal, study design information, sample size, disease stage, treatments (dose, duration time, and frequency), detailed information of participants (median age, hormone receptor status, postmenopausal status, human epidermal growth factor receptor‐2 status, ethnicity, and histological type), and specific outcomes (response rate, treatment completion, and BCS).The response rate was defined as the percentage of patients who achieved complete remission and/or partial remission, which was measured according to response evaluation criteria in solid tumours (RECIST), Union for International Cancer Control (UICC), and World Health Organization (WHO) criteria. Treatment completion was defined as the number of patients who completed treatments. After all data extraction was completed, the two authors cross‐checked all data to ensure its accuracy.

We evaluated the risk of bias using the Cochrane Collaboration's risk of bias assessment tool (Higgins et al., 2011). In general, the following domains were used for evaluation: random sequence generation; allocation concealment; blinding (participants, personnel, and outcome assessment); incomplete outcome data; and selective reporting and other bias. These domains were categorised as having a high, low, or unclear risk of bias.

2.4. Statistical Methods

The primary and secondary outcomes were response rate and treatment completion, respectively. We directly extracted the number of incidents and total sample size from the included studies. If only percentages were reported, rounding was required to estimate the number of incidents instead of the actual number. In brief, we pooled the effect size using the odds ratio (OR) because all outcomes of interest were binary variables.

To compare the differences between direct and indirect evidence for a certain set of interventions, we applied a node‐splitting method to assess whether there were any inconsistencies. In addition, we calculated the corresponding p value to evaluate differences between direct and indirect evidence. If the p > 0.05, then we considered that there was no significant inconsistency (Dias, Welton, Caldwell, & Ades, 2010). Therefore, based on the random effect Bayesian model provided with the GeMTC 0.14.3 software, (van Valkenhoef et al., 2012) we used a consistency model for analysis and merged the direct and indirect evidence. We used ORs and the corresponding 95% credibility intervals (CrIs) to estimate both the response rate of NET in postmenopausal breast cancer and the completion of treatment throughout the trials. Furthermore, we used the surface under the cumulative ranking curves (SUCRA) value to define the rank of all treatments. If the SUCRA of treatment was closer to 100, it indicated that it should always occur first, whereas values that were closest to 0 should be last (Salanti, Ades, & Ioannidis, 2011).

A network plot was drawn with STATA version 13.0 software (Stata Corporation, College Station, TX), in which the line width is proportional to the number of trials that compare every pair of treatments and the size of the node is proportional to the number of patients assigned to receive treatment. Other calculations were conducted using GeMTC version 0.14.3. For methodological assessments, Review Manager version 5.3 (The Nordic Cochrane Centre: The Cochrane Collaboration, Copenhagen, Norway) was used to evaluate the risk of bias for each assessment.

3. RESULTS

The PRISMA flowchart illustrates the literature search scheme and study selection details on the basis of inclusion and exclusion criteria (Figure 1). Overall, 12,888 potentially relevant citations were identified by the search and, after duplicates were removed, 1,193 citations were excluded. After first reviewing the titles and abstracts, we further excluded 11,611 publications. A total of 84 publications were selected for further review of the entire text. Of these, 68 publications were excluded for the following specific reasons: inappropriate participants (n = 3), nondesired outcomes reported (n = 22), nonrandomised controlled trials (RCTs) (n = 5), from the same trial (n = 14), the desired intervention agent was not in the study (n = 13), and unfinished studies (n = 11). Ultimately, 16 studies (Alba et al., 2012; Baselga et al., 2009; Cataliotti et al., 2006; Chow, Yip, Loo, Lam, & Toi, 2008; Eiermann et al., 2001; Ellis et al., 2001; Ellis et al., 2011; Fasching et al., 2014; Guarneri et al., 2014; Hojo et al., 2013; Lerebours et al., 2016; Palmieri, Cleator, et al., 2014; Polychronis et al., 2005; Saura et al., 2017; Smith et al., 2005, 2007) met our inclusion criteria and were included in our network meta‐analysis.

Figure 1.

Flowchart for search results and selection details. RTC: nonrandomised controlled trial

3.1. Characteristics

Detailed characteristics of qualified studies in the network meta‐analysis are summarised in Table 1. The included trials were mostly multicentre, open‐label trials, although they varied considerably in terms of sample size. In total, our study involved 16 RCTs with 3,306 participants. The included trials were published from 2001 to 2017. The median age across the studies ranged from 50.5 to 73.2, except one study that did not report the age of participants. Relevant interventions included the following agents: chemotherapy, letrozole, anastrozole, exemestane, tamoxifen, gefitinib, lapatinib, taselisib, fulvestrant, celecoxib, everolimus, and zoledronic acid. Regarding hormone receptor status, only five studies did not report it, and the percentages in the remaining reports ranged from 22.7% to 100%. The primary end point in the majority of studies was the response rate.

Table 1.

Characteristics of 15 included RCTs in network meta‐analysis

Authors	Clinical stage	Median age (years)	Arm	Sample size	HR status (%)	HER‐2 status (%)	Primary end point
Palmieri (2014)	T2/above/any T stage with nodal ≥20 mm diameter	59.8 (55.1–5.6)	Letrozole	22	ER+/PR+:63.6	+:9.1	Feasibility OR (by US or mammography based on RECIST criteria v1.1) was a secondary end point
					ER+/PR−:31.8	–:90.9
			CT	22	ER+/PR+:7.7	+:9.1
					ER+/PR−:22.7	−:81.8
Eiermann (2001)	T2‐4a‐c, N0‐2, M0	68	Letrozole	154	ER+ and/ or PR+:100	NR	OR by clinical palpation OR by US/mammography was a secondary end point
		67	Tamoxifen	170	ER+ and/ or PR+:99	NR
Smith (2005)	LABC	73.2 (51.8–90.2)	Anastrozole	113	ER+:98.2	NR	OR by caliper assessment based on WHO criteria OR by US was a secondary end point
		71.5 (49.8–88.4)	Tamoxifen	108	ER+:99.1	NR
		73.2 (51.6–85.7)	Tamoxifen + anastrozole	109	ER+:96.3	NR
Cataliotti (2006)	LABC	67.3 (48.7–91.5)	Anastrozole	228	ER+/PR+:69.7	NR	OR based on US by RECIST criteria
					ER+/PR−:24.6
		66.7 (44.1–95.9)	Tamoxifen	223	ER+/PR+:68.2	NR
					ER+/PR−:26.5
Smith (2007)	I–IIIB	69.8	Anastrozole + gefitinib	121	ER+:97	+:10.2	Change in Ki67. Secondary end point was OR (modality not specified) based on UICC/WHO criteria
					PR+:61
		70.3	Anastrozole	85	ER+:98	−:89.8
					PR+:79
Chow (2008)	Invasive BC	69 (49–87)	Exemestane(<20 weeks) + celecoxib	30	ER+:100	+:20	OR by caliper assessment based on UICC criteria
					PR+:73	−:80
		67 (48–91)	Exemestane(<20 weeks)	24	ER+:100	+:8
					PR+:54	−:92
		75 (49–93)	Letrozole	28	ER+:100	+:7
					PR+:89	−:93
Baselga (2009)	M0	69 (46–88)	Letrozole + everolimus	138	–	NR	OR based on palpation by WHO criteria OR also assessed by US/mammography
		67 (43–84)	Letrozole	132	–	NR
Ellis (2011)	T2‐T4c, N0‐3, M0	69 (43–90)	Exemestane( < 20weeks)	124	–	+:6.5	OR by clinical assessment based on WHO criteria
						−:90.3
		65 (49–90)	Letrozole	127	–	+:10.2
						−:85.8
						+:9.8
		65 (51–87)	Anastrozole	123	–	−:87.8
Hojo (2013)	IIA–IIIA	66 (51–80)	Exemestane( < 20weeks)	26	ER+:100	NR	OR by caliper assessment based on RECIST criteria
					PR+:76.9
		64 (57–80)	Exemestane( ≥ 20weeks)	26	ER+:96.2	NR
					PR+:69.2
Saura (2017)	I–III	64.6	Letrozole + taselisib	166	–	−:100	OR by centrally assessed breast MRI/RECIST v1.1
		64.7	Letrozole	168	–	−:100
Fasching (2014)	Invasive BC	70 (54.0–88.0)	Letrozole + zoledronic acid	81	ER+:96.6	NR	OR by mammography based on RECIST criteria v1.0
					PR+:90.8
		71 (54.0–89.0)	Letrozole	75	ER+:97.0	NR
					PR+:89.4
Alba (2012)	–	50.5 (33–72)	Exemestane	48	–	−:100	OR by MRI based on RECIST criteria v1.0
		51 (32–74)	CT	47	–	−:100
Ellis (2001)	Primary BC	–	Letrozole	154	ER+:60	NR	OR by clinical assessment based on WHO criteria OR by US/mammography was a secondary end point
					PR+:62.9
		–	Tamoxifen	170	ER+:39.8	NR
					PR+:42.9
Polychronis (2005)	–	63.4	Anastrozole + gefitinib	27	ER+:100	NR	Change in Ki67. Secondary end points included clinical and US assessments
					PR+:70.4
		64.7	Gefitinib	29	ER+:100	NR
					PR+:72.4
Lerebours (2016)	M0	70.7 (53–92)	Anastrozole	59	–	−:100	OR by mammography/US/MRI/RECIST v1.0
		72.5 (51–88)	Fulvestrant	57	–	−:100
Guarneri (2014)	II–IIIA	70 (49–88)	Letrozole + lapatinib	43	ER+:89	−:100	OR based on US by RECIST criteria
					PR+:56
		70 (47–88)	Letrozole	49	ER+:90	−:100
					PR+:52

Note. BC: breast cancer; CT: chemotherapy; ER+: oestrogen receptor positive; LABC: locally advanced breast cancer; NR: not reported; PR+: progesterone receptor positive; OR: overall response rate; RECIST v1.1: response evaluation criteria in solid tumours version 1.1; UICC: Union for International Cancer Control; US: ultrasonography; WHO: World Health Organization.

3.2. Quality assessments

The risk of bias in all 16 studies is shown in Figure 2. The methodology quality of the studies was rated as high, although some studies did not describe details about random sequence generation or adequate allocation concealment. Most trials had an unclear risk of bias. For the blinding of participants and personnel, six studies (Alba et al., 2012; Baselga et al., 2009; Ellis et al., 2011; Fasching et al., 2014; Hojo et al., 2013; Palmieri, Cleator, et al., 2014) were at a high risk of bias and seven studies (Baselga et al., 2009; Cataliotti et al., 2006; Eiermann et al., 2001; Guarneri et al., 2014; Polychronis et al., 2005; Saura et al., 2017; Smith et al., 2005) were at a low risk of bias. However, for the blinding of outcome assessments, only two studies (Polychronis et al., 2005; Smith et al., 2005) had a low risk of bias. We considered that the majority of studies had a low risk of bias for outcome data and selective reporting. Additionally, eight studies (Cataliotti et al., 2006; Chow et al., 2008; Eiermann et al., 2001; Ellis et al., 2001; Fasching et al., 2014; Saura et al., 2017; Smith et al., 2005) had an unclear risk of bias for “other bias.”

Figure 2.

Cochrane risk of bias tool assessment (+: low risk of bias;−: high risk of bias; ?: unclear risk of bias) [Color figure can be viewed at wileyonlinelibrary.com]

3.3. Network meta‐analysis

3.3.1. Response rate

Figure 3 shows the network of eligible comparisons for response rates of the network meta‐analysis. The networks for treatment completion and response rate for dichotomous outcomes were essentially the same. A total of 15 treatments were involved, of which seven were combined and eight were monotherapy. Among all compared treatments, letrozole was the most frequently compared drug. Based on the node‐splitting method, we evaluated disagreements between direct and indirect evidence. As the p > 0.05, there was consistency between direct and indirect comparisons.

Figure 3.

Network of eligible comparisons for network meta‐analysis for response rate [Color figure can be viewed at wileyonlinelibrary.com]

The 16 analysed studies included 3,306 patients that contributed to the analysis of response rates. As is shown in Table 2, letrozole was superior to tamoxifen (OR, 2.00; 95% CrI, 1.25–3.33). Tamoxifen was associated with a significant reduction in response rate compared with letrozole combined therapy (OR, 0.34; 95% CrI, 0.13–0.85; OR, 0.32; 95% CrI, 0.13–0.80; OR, 0.26; 95% CrI, 0.09–0.83; OR, 0.30; 95% CrI, 0.09–0.96; for letrozole plus everolimus, letrozole plus taselisib, letrozole plus zoledronic acid, and letrozole plus lapatinib, respectively). However, tamoxifen did not differ statistically compared with anastrozole (OR, 0.74; 95% CrI, 0.45–1.21), exemestane (<20 weeks; OR, 0.95; 95% CrI, 0.46–1.99), exemestane (≥20 weeks; OR, 1.07; 95% CrI, 0.32–3.90), gefitinib (OR, 0.89; 95% CrI, 0.12–5.34), or fulvestrant (OR, 1.34; 95% CrI, 0.48–4.25). Moreover, anastrozole plus gefitinib was also associated with a lower rate of response than that noted with exemestane (<20 weeks) pluscelecoxib (OR, 0.21; 95% CrI, 0.04–0.84), exemestane (<20 weeks; OR, 0.30; 95% CrI, 0.09–0.98), letrozole plus everolimus (OR, 0.11; 95% CrI, 0.03–0.37), letrozole plus taselisib (OR, 0.10; 95% CrI, 0.03–0.36), letrozole plus zoledronic acid (OR, 0.08; 95% CrI, 0.02–0.34), or letrozole plus lapatinib (OR, 0.10; 95% CrI, 0.02–0.41). Additionally, letrozole, tamoxifen, anastrozole, and anastrozole plus tamoxifen were significantly superior to anastrozole plus gefitinib.

Table 2.

Network meta‐analysis comparison of neoadjuvant endocrine therapies for response rate and treatment completion

Let	1.30	2.02	1.49	1.49	6.72	1.20	1.89	0.68	2.17	0.63	0.53	2.04	2.86	0.55
	(0.39, 5.09)	(1.24, 3.38)	(0.85, 2.73)	(0.65, 3.77)	(2.31, 20.97)	(0.40, 3.61)	(1.02, 3.50)	(0.29, 1.57)	(0.63, 7.32)	(0.30, 1.46)	(0.17, 1.36)	(0.29, 22.14)	(0.93, 9.05)	(0.19, 1.62)
1.22	CT	1.58	1.16	1.24	5.27	0.94	1.46	0.52	1.71	0.49	0.39	1.58	2.19	0.41
(0.40, 4.98)		(0.38, 5.44)	(0.28, 4.01)	(0.25, 4.90)	(0.92, 23.41)	(0.17, 3.81)	(0.37, 4.80)	(0.10, 2.10)	(0.62, 4.17)	(0.10, 1.99)	(0.07, 1.89)	(0.15, 15.98)	(0.38, 10.20)	(0.08, 1.87)
2.00	1.69	Tam	0.74	0.75	3.35	0.60	0.93	0.34	1.09	0.31	0.26	1.02	1.43	0.27
(1.25, 3.33)	(0.38, 5.59)		(0.45, 1.23)	(0.35, 1.71)	(1.21, 9.57)	(0.18, 1.90)	(0.45, 1.91)	(0.12, 0.86)	(0.29, 3.87)	(0.13, 0.85)	(0.08, 0.76)	(0.14, 10.65)	(0.48, 4.26)	(0.09, 0.86)
1.49	1.19	0.74	Ana	1.05	4.54	0.79	1.26	0.45	1.49	0.43	0.35	1.37	1.93	0.36
(0.87, 2.65)	(0.28, 4.21)	(0.45, 1.21)		(0.47, 2.20)	(1.85, 11.32)	(0.24, 2.60)	(0.62, 2.51)	(0.16, 1.28)	(0.42, 5.19)	(0.16, 1.20)	(0.10, 1.08)	(0.22, 13.20)	(0.73, 4.99)	(0.11, 1.24)
1.51	1.21	0.74	1.01	Ana+Tam	4.33	0.77	1.22	0.45	1.42	0.42	0.34	1.31	1.85	0.35
(0.58, 3.74)	(0.24, 5.32)	(0.35, 1.65)	(0.49, 2.16)		(1.31, 14.68)	(0.20, 2.98)	(0.48, 3.22)	(0.13, 1.44)	(0.34, 5.83)	(0.13, 1.36)	(0.09, 1.19)	(0.18, 16.64)	(0.54, 6.34)	(0.09, 1.42)
6.28	4.95	3.12	4.28	4.39	Ana+Gef	0.17	0.28	0.10	0.33	0.09	0.08	0.31	0.42	0.08
(2.25,18.50)	(0.94, 24.41)	(1.15, 8.78)	(1.84, 10.51)	(1.30, 13.57)		(0.04, 0.79)	(0.09, 0.89)	(0.02, 0.38)	(0.07, 1.51)	(0.03, 0.38)	(0.02, 0.33)	(0.06, 2.17)	(0.11, 1.67)	(0.02, 0.39)
1.33	1.10	0.67	0.88	0.87	0.21	Exe a +Cel	1.58	0.58	1.84	0.52	0.43	1.64	2.38	0.46
(0.41, 3.74)	(0.18, 4.68)	(0.18, 2.00)	(0.25, 2.71)	(0.21, 3.06)	(0.04, 0.84)		(0.52, 4.86)	(0.15, 2.24)	(0.43, 8.54)	(0.14, 2.17)	(0.10, 1.89)	(0.20, 21.01)	(0.55, 11.42)	(0.11, 2.21)
1.93	1.57	0.95	1.29	1.25	0.30	1.47	Exe a	0.36	1.17	0.33	0.28	1.09	1.53	0.29
(0.98, 3.60)	(0.39, 4.96)	(0.46, 1.99)	(0.66, 2.59)	(0.46, 3.83)	(0.09, 0.98)	(0.51, 4.58)		(0.13, 1.02)	(0.35, 3.47)	(0.13, 0.95)	(0.09, 0.86)	(0.16, 13.77)	(0.44, 5.03)	(0.09, 0.98)
0.66	0.57	0.34	0.46	0.45	0.11	0.50	0.35	Let+Eve	3.20	0.92	0.80	3.02	4.32	0.80
(0.30, 1.50)	(0.11, 2.16)	(0.13, 0.85)	(0.16, 1.20)	(0.13, 1.45)	(0.03, 0.37)	(0.14, 2.15)	(0.12, 0.95)		(0.69, 14.31)	(0.31, 3.06)	(0.19, 2.68)	(0.37, 41.30)	(0.98, 17.53)	(0.23, 3.21)
2.14	1.78	1.07	1.46	1.38	0.33	1.69	1.14	3.27	exe b	0.29	0.24	0.91	1.26	0.24
(0.71, 7.30)	(0.63, 4.50)	(0.32, 3.90)	(0.44, 5.04)	(0.35, 5.91)	(0.08, 1.63)	(0.38, 8.37)	(0.39, 3.42)	(0.83, 13.36)		(0.07, 1.37)	(0.05, 1.21)	(0.10, 10.52)	(0.26, 6.92)	(0.05, 1.20)
0.65	0.55	0.32	0.44	0.43	0.10	0.48	0.33	0.97	0.29	Let+Tase	0.85	3.19	4.54	0.86
(0.29, 1.43)	(0.10, 2.01)	(0.13, 0.80)	(0.17, 1.11)	(0.13, 1.34)	(0.03, 0.36)	(0.14, 1.99)	(0.12, 0.90)	(0.31, 2.99)	(0.07, 1.16)		(0.22, 2.76)	(0.39, 43.47)	(1.12, 17.30)	(0.24, 3.04)
0.52	0.44	0.26	0.36	0.36	0.08	0.40	0.27	0.78	0.24	0.83	Let+Zol	3.80	5.34	1.06
(0.20, 1.36)	(0.08, 1.77)	(0.09, 0.83)	(0.12, 1.09)	(0.09, 1.22)	(0.02, 0.34)	(0.10, 1.83)	(0.08, 0.89)	(0.23, 2.59)	(0.05, 1.10)	(0.23, 2.73)		(0.48, 61.13)	(1.10, 31.06)	(0.25, 4.41)
1.67	1.43	0.89	1.22	1.17	0.28	1.25	0.87	2.55	0.74	2.58	3.33	Gef	1.38	0.27
(0.24, 11.29)	(0.14, 12.50)	(0.12, 5.34)	(0.17, 6.96)	(0.14, 7.92)	(0.04, 1.23)	(0.15, 11.67)	(0.11, 6.30)	(0.31, 20.15)	(0.09, 6.94)	(0.32, 20.82)	(0.32, 28.17)		(0.10, 10.88)	(0.02, 2.45)
2.74	2.17	1.34	1.85	1.85	0.43	2.12	1.43	4.05	1.28	4.15	5.00	1.60	Fulv	0.19
(0.91, 8.99)	(0.43, 12.00)	(0.48, 4.25)	(0.74, 5.08)	(0.58, 6.18)	(0.12, 1.71)	(0.50, 10.83)	(0.42, 4.86)	(1.13, 17.47)	(0.28, 5.97)	(1.12, 17.50)	(1.26, 24.22)	(0.21, 13.16)		(0.04, 0.88)
0.61	0.49	0.30	0.41	0.39	0.10	0.46	0.31	0.91	0.25	0.95	1.15	0.37	0.22	Let+Lap
(0.19, 1.76)	(0.08, 2.27)	(0.09, 0.96)	(0.11, 1.31)	(0.09, 1.54)	(0.02, 0.41)	(0.10, 2.14)	(0.08, 1.08)	(0.23, 3.19)	(0.05, 1.38)	(0.23, 3.35)	(0.26, 4.56)	(0.03, 3.92)	(0.04, 1.01)

Note. The results are presented as the odds ratio (OR) and 95% credible interval (CrI) for response rate (lower left quarter) and as the OR and 95% CrI for treatment completion (upper right quarter). For response rate, ORs >1 favour the column‐defining treatment (i.e.,The ORs of letrozole compared with tamoxifen were 2.00, which favour letrozole treatment). For treatment completion, ORs >1 favour the row‐defining treatment (The ORs of letroole compared with tamoxifen were 2.02, which favour tamoxifen treatment). Bold entries mean ORs and HRs are statistically significant.

Ana: anastrozole; Ana + Gef: anastrozole plus gefitinib; Ana + Tam: anastrozole plus tamoxifen; CT: chemotherapy; Exe^a: exemestane (<20 weeks); Exe^b: exemestane (≥20 weeks); Exe^a + Cel: exemestane (<20 weeks) plus celecoxib; Fulv: fulvestrant; Gef: gefitinib; Let: letrozole; Let + Eve: letrozole plus everolimus, Let + Lap: letrozole plus lapatinib; Let + Tase: letrozole plus taselisib; Let + Zol: letrozole plus zoledronic acid; Tam: tamoxife.

Based on the SUCRA ranking, letrozole plus zoledronic acid was associated with the highest rate of response (87.6%), followed by letrozole plus lapatinib (85.2%), and letrozole plus taselisib (79.3%). The detailed ranking is shown in Figure 4a.

Figure 4.

The SUCRA for response rate (a) and treatment completion (b). The larger the SUCRA, the higher the ranking. SURCA: surface under the cumulative ranking curves

3.4. Treatment completion

For treatment completion, the ORs were greater for letrozole, tamoxifen, anastrozole, and anastrozole plus tamoxifen than for anastrozole plus gefitinib. In addition, anastrozole plus gefitinib was inferior to exemestane (<20 weeks) plus celecoxib (OR, 0.17; 95% CrI, 0.04–0.79), exemestane (<20 weeks) (OR, 0.28; 95% CrI, 0.09–0.89), letrozole plus everolimus (OR, 0.10; 95% CrI, 0.02–0.38), letrozole plus taselisib (OR, 0.09; 95% CrI, 0.03–0.38), letrozole plus zoledronic acid (OR, 0.08; 95% CrI, 0.02–0.33), and letrozole plus lapatinib (OR, 0.08; 95% CrI, 0.02–0.39). Exemestane (<20 weeks) showed no advantage compared toletrozole plus taselisib (OR, 0.33; 95% CrI, 0.13–0.95), letrozole plus zoledronic acid (OR, 0.28; 95% CrI, 0.09–0.86), or letrozole plus lapatinib (OR, 0.29; 95% CrI: 0.09–0.98).

Regarding treatment completion, a detailed ranking is presented in Figure 4b. Based on the SUCRA value ranking, tamoxifen was the best (SUCRA = 74.8%), followed by fulvestrant (SUCRA = 71.2%), and anastrozole (SUCRA = 60.6%).

4. DISCUSSION

Endocrine therapy is a key therapeutic modality for ER+ breast cancer and NET, with lower toxicity and good tolerability, which could represent an attractive alternative to NCT for ER+ breast cancer tumours (Palmieri, Patten, Januszewski, Zucchini, & Howell, 2014). Here, we performed a network meta‐analysis of the efficacy and acceptability of NET. We drew the following important conclusions from our network meta‐analysis. First, in terms of the response rate, letrozole plus zoledronic acid should be the first choice for endocrine therapy in the general population of patients with ER+ breast cancer. Second, also in terms of the response rate, letrozole plus lapatinib might be considered as a second‐choice treatment, whereas tamoxifen might be considered as the optimal choice of treatment on the basis of treatment completion. However, data from a previous network meta‐analysis suggested that letrozole plus everolimus might be the optimal treatment for patients with postmenopausal, HR+ breast cancer in a neoadjuvant setting (Wang et al., 2012).

Zoledronic acid is a type of bisphosphonate that is used to manage solid tumours with bone metastases (Osborne, 2002). A previous report indicated that bisphosphonates may prevent recurrence in breast cancer at peripheral sites and suggested that they may have antitumour activities outside the skeletal system (Holen & Coleman, 2010). In several studies, it has been demonstrated that these compounds have the ability to reduce cell proliferation, inhibit cell migration, and induce apoptosis (Russell, 2007). Neville‐Webbe, Evans, Coleman, and Holen (2006) and Ottewell et al. (2008) found using in vitro or in vivo animal models that the combination of zoledronic acid and paclitaxel had a synergistic effect in inducing breast cancer cell apoptosis. Notably, this study solely focused on premenopausal women in the ABCSG‐12 trial, which demonstrated that for patients with ER+ early breast cancer, the addition of zoledronic acid to anastrozole or tamoxifen regimens improved disease‐free survival (Gnant et al., 2009). Similarly, the AZURE trial investigated the efficacy of the addition of zoledronic acid to standard adjuvant treatments, and suggested that it did reduce the development of bone metastases and improve disease outcomes for women with established menopause (Coleman et al., 2014). A randomised phase II trial showed a trend towards a better response for zoledronic acid combined with letrozole (Fasching et al., 2014).

Regarding the quality of selected trials, in 11 of 16 trials, both sequence generation and allocation concealment were considered to be unclear. However, not only were the patient characteristics in each trial distributed equally in each treatment group, but we also used objective evaluation methods; therefore, the impact of uncertain factors could be regarded as insignificant. Additionally, according to the node‐splitting method, the p > 0.05, demonstrating that there was consistency between the direct and indirect evidence. Although a previous network meta‐analysis (Wang et al., 2012) was conducted involving HR + NET for breast cancer, our study ultimately established the optimal sequence of NET by adding updated randomised controlled trials in the neoadjuvant setting of HR+ breast cancer.

Our network meta‐analysis has a number of strengths. We used a comprehensive, systematic, and unbiased search strategy with relevant databases. Moreover, using a rigorous selection criterion, we only included high quality RCTs. This study provides insight into the optimal NET for HR+ breast cancer; however, it certainly has several limitations. First, our study only analyses response rates and treatment completion as measures of efficacy, but it also needs separate clinical trials to confirm the surrogacy relation of the response rate with survival data in the future. Second, in all trials, response rates were not assessed uniformly, but most of them used the evaluation criteria of RECIST or WHO. Therefore, no evidence of significant publication bias was found. Third, the number of eligible studies and participants included was relatively small, which limited the informative value of the direct comparisons of the letrozole plus zoledronic acid‐containing arms. Finally, the number of studies that reported BCS was limited overall and, therefore, they were not evaluated in the network meta‐analysis. Additionally, the optimal sequence for BCS was not determined.

5. CONCLUSIONS

In conclusion, our study ultimately established that letrozole plus zoledronic acid may be considered an optimal treatment in the neoadjuvant setting of HR+ breast cancer based on its current rank by adding randomised clinical data. Despite the limited number of letrozole plus zoledronic acid‐related randomised controlled trials, we believe that our network meta‐analysis results can contribute to evidence‐based decision making in clinical practice.

CONFLICT OF INTEREST

The authors declared that there are no conflicts of interest.

AUTHOR CONTRIBUTIONS

Substantial contribution to the conception and design of the work: Z. T. T., and S. C. G. Analysis and interpretation of the data: Z. T. T. and D. S. J. Drafting the manuscript: Z. T. T. Revising the work critically for important intellectual content: F. F. B., Y. Y., and Q. L. Y. Final approval of the work: All the authors.

Supporting information

Supplementary information

Supplementary information

Supplementary information