Sequential Vs Concurrent Adjuvant Chemotherapy for Operable Breast Cancer: A Meta-analysis

Backgroud: Controversy still remains in that whether sequential or concurrent regimen of anthracyclines and taxanes benets more for breast cancer. Here we aimed to compare these two regimens in patients with operable breast cancer based on all published data of phase III randomized controlled trials in this topic. Methods: A literature search on PubMed, Web of science, Embase, ScienceDirect, Google scholar and clinicaltrials.gov databases was conducted up to May 2020. Meta-analysis was performed to evaluate the different ecacy on disease free survival (DFS) and overall survival (OS)for these two regimens. Subgroup analyses were further carried out in terms of node status and anthracycline selection. Results: Compared to concurrent regimen, sequential regimen did not improve the DFS or OS in the whole population included. Subgroup analysis showed that in node-positive patients, however, sequential regimen has better DFS, but not OS, than concurrent regimen.In sequential regimen, patients received doxorubicin and taxanes had improved DFS and OS than those were given epirubicin and taxanes. Futhermore, for patients receiving doxorubicin and taxanes,compared to sequential regimen,less cycles (4 cycles) of concurrent treatment showed worse DFS and OS, whereas more cycles(6 cycles) may rescue the loss.In addition,high grade toxicity response in both groups exhibited no difference except for neuropathy, which occured more frequently in the sequential regimen. Conclusions:Sequential regimen of anthracyclines and taxanes for patients with breast cancer did not promise a signicant benet in neither DFS nor OS over concurrent regimen. However, sequential regimen did provide a better DFS than that in concurrent regimen for node-positive patients. Interestingly, further subgroup analysis showed that for patients with node-positive and were given doxorubicin and taxanes, more cycles (6 cycles) of concurrent reigmen was not inferior to sequential regimen.


Background
Breast cancer is the most common cancer in women worldwide.In 2018, 266,120 new breast cancer cases occurred in the United States, accounting for 30% of all female malignant tumors, and 40,920 deaths, accounting for 14% of the total mortality of female malignancies [1]. In China,the incidence and the mortality of female breast cancer is about 41.82/100,000and 9.91/100,000, respectively [2]. Despite of the great advances achieved in diagnosis and treatment, breast cancerremains to be one of the leading causes of cancer-related death [1]. Dozens of studies have indicated that adjuvant chemotherapy contributeshuge bene t for early breast cancer patients aftersurgery [3], and at present, anthracyclines and taxanes are the basic components in chemotherapy as the addition of a taxane to an anthracyclinecontained regimen is assoiciated with better relapse-free and overall survival [4][5][6][7]. However, although the regimens containing anthracycline and taxaneare reported to be more effective, the optimal schedule ofdrug intervention (sequentially or concurrently)remains questionable. For instance, super cially at least, concurrent regimen requires less doses of durgs which may affect the e ciency,nevertheless,sequential administrationmay supply an optimal dose for each compound but requireslonger time frame.
Thus, to elucidate clearly which regimen may promise more bene t for patients, we performed this metaanalysis to comprehensively evaluate the clinical effect of these two adjuvant regimens in patients after breast cancer surgery by including all phase randomized control studies in this topic.

Methods
The methods used for this meta-analysis and generation of inclusion criteria were based on PRISMA recommendations.

Literature search strategy
Databases including PubMed, Web of science, Embase, ScienceDirect, Google scholar and clinicaltrials.gov up to May 2020 were used for literature search, with the following keywords: "breast cancer", "sequential and (concurrent or concomitant)", "adjuvant chemotherapy","anthracyclines and taxanes", "(doxorubicin or epirubicin) and (docetaxel or paclitaxel)". In addition, the references of relevant reviews were searched for additional studies.

Inclusion and exclusion criteria
The inclusion criterias are as follows: (1) Phase III randomized control studies; (2) Breast cancer that have not spreaded beyond the breast or the axillary lymph nodes. (3) Patients whom underwent curative surgical resection and were subsequently randomized to receive either sequential or concurrent regimen.
Standard post-operative radiotherapy and endotherapy protocols, either with tamoxifen or aromatase inhibitors,were allowed.

Data extraction
Two investigators independently screened all the studies and extracted data. Differences were resolved by discussion until obtaining consistence. The following data were extracted and recorded in a predesigned form: study design,year of reporting, regimen details, median follow up, hazard ratio(HR) of DFS and OS, the number of outcome events, and the number of patients who experienced grade 3 and 4 toxicity.

Quality assessment
We used The Cochrane Collaboration's 'Risk of bias' assessment tool to assess the potential sources of bias in the included studies [7].Two authors independently assessed the potential risk of bias for each study; any differences in judgement were resolved through discussion.The domains assessed according to random sequence generation,allocation concealment,blinding of participants and personel,blinding of outcome assessment,incomplete outcome data,selective reporting,and other bias.We assigned rating of "high", "low" or "unclear" risk of bias to each domain for each included studies.

Statistical analysis
The RevMan 5.3 was used for performing this meta-analysis. The I 2 and Cochrane Q tests were used to assess heterogeneity among the included studies, with P<0.1or I 2 > 50% being considered as signi cant.
The risk radio (RR) as well as the corresponding 95% con dence intervals (CIs) were pooled by an appropriate model ( xed-or random-effects model) based on the results of the heterogeneity test. Z test was used to evaluate the signi cant of pooled effect size. For dichotomous variables, a Mantel-Haenszel Rate Ratio with 95% con dence intervals was calculated. If signi cant heterogeneity was detected (P<0.1), causes of heterogeneity were subsequently explored via subgroup analyses, otherwise a random effect model was selected. For continuous variables, we used a xed effect weighted mean difference (WMD) for measurements and 95% con dence interval (95% CI) was calculated.
All analysis were performed according to the intention-to-treat principle, when appropriate data were available. The publications bias was evaluated by the Egger's and Begg's test using Stata 11.0 software. The sensitivity analyses were performed by omitting each individual study at a time. For these analyses, p<0.05 indicated statistical signi cance.

Characteristics of the included studies
After an initial literature search on PubMed, Web of science, Embase, ScienceDirect, Google scholar and clinicaltrials.gov databases, 189 articles were identi ed. After excluding duplicates and obvious irrelevant studies, 59 potentially relevant articles were remained. Among these, 32 articles were further excluded due to mis-matching contents (21 studies did not report the comparison between sequential and concurrent regimens; 8 reviews; 3 case reports). For the rest 27 articles, another 21 studies were excluded for the following reasons: no available data (n=7); no comparison between sequential and concurrent regimens(n=4); regimens did notcontain both anthracycline and taxane(n=8); duplicates(n=2). Finally, 6 articles wereincluded in this meta-analysis [8][9][10][11][12][13] (Figure 1).
In these 6 studies, 6866 breast cancer patients after surgery were given sequential regimen of anthracyclines and taxanes as adjuvant chemotherapy, while 6847 patients were received concurrent treatment( Table 1). The publication year ranged from 2010 to 2017. All these studies were phase III randomized control trials.

Quality assessment
The details of the risk of bias summary wasoutlined( Figure 2).All studies were considered to be at median risk of bias.Randomized sequence generation was implemented in all 6 studies,and 4 studies implemented allocation concealment.All studies were performed on the intention-to-treat principle.None of these 6 studies reported blind to the participants or the outcome assessment.

Comparison of DFS between sequential and concurrent regimens
Signi cant heterogeneity among studies (I 2 =59%, P =0.03, Figure 3) was found in analysis for DFS between sequential and concurrent regimens, so we used the random effects model to pool the RR. The meta-analysis showed that sequential regimens of anthracycline and taxane seems not to add any signi cant improvement in DFS over to the concurrent regimens(RR: 1.05; 95%CI:0.97-1.14; P=0.22, Figure  3).

Comparison of DFS between sequential and concurrent regimens
As shown in Figure 4, signi cant heterogeneity among studies was observed for OS in comparison between sequential and concurrent regimens (I 2 =55%, P =0.05, Figure 4), so the randomized effects model should be used. The pooled estimate showed that there are no signi cant different OS between sequentialregimens compared withconcurrent regimens(RR: 1.03, 95% CI: 0.94 to 1.13, P =0.51, Figure 4).

Sub-analysis in node status for DFS and OS
Eligible patients in HORG trial [11]were early breast cancer patients with high risk and node-negative, while the other trials included patients with node-positive.We conducted a sub-analysis according to the axillary lymph node status. The pooled estimate showed that there wasa signi cant better DFS in patients with node-positive administrated with sequential regimens (RR: 1.08;95%CI:1.02-1.14, P=0.004, Figure 5A),yet the OS were approximate between both regimens (RR: 1.07;95%CI:0.96-1.19, P=0.24, Figure 5B).
The cycles of concurrent regimen with doxorubicin and taxanes also seemed to affect the heterogenity.

Comparison of toxicity between sequential and concurrent regimens
Both hematologic and non-hematologic grades 3 and 4 adverse events were described in the six studies. Using prophylactic Granulocyte colony stimulating factor(G-CSF),patients with concurrent treatment did not show any signi cant higher risk of hematologic complications, such as febrile neutropenia and anemia.There was also no signi cant difference for fatigue or diarrhea.Nevertheless, the incidence of neuropathyoccuered more frequentlyin the sequential regimen(RR = 0.17, 95% CI: 0.12 to 0.24, P <0.00001, Table 2).

Sensitivity analysis and publication bias
Sensitivity analysis showed that there was no signi cantly different incidence through omitting each study. No signi cant publication bias was found based on the Egger's and Begg's test (P > 0.05, Figure 8).

Discussion
Controversy still remains in that whether sequential or concurrent usage of anthracyclines and taxanes contributes more for operable breast cancer patients' survival.Our meta-analysis presented evidencesthat the sequential regimen is not associated with better DFS or OS than concurrent regimen from any cause, according to all published data of phase III randomized controlled trials.
Consideringthe importance of axillary lymphnode status on breast cancer recurrence, DFS and OS,we conducted a sub-analysis to illuminate whether node-positive or -negative would affect the result.Data from 5 included phase III trials showed thatin node-positive patients, sequential treatment provided a statistically better DFS. We further conducted another subgroup analysisin node-positive patientsin regard todifferent choice of anthracycline.In particular, data from four trials [8][9][10]12]showedpatientstreated with doxorubicin get bothbetter DFS and OS than whom were treated with epirubicin.Interestingly, in the doxorubicin groupgiven four cycles of drug treatment [9,10], patients in sequential arm achievedbetter DFS and OS compared to combination arm, whereas patients receiving six concurrent cycleshad the similar survival with the sequential group [8,12].This may be explained by two reasons.Firstly and importantly,cumulative doses of drugs would be the main factor.For patientsin Big 02-98 [10] and NSABP B-30 [9] trials, the sequential arms were delivered with higher cumulative doses of both validated the nding from NEAT trial [16] that a higher dose intensity confers a greater favorable long-term outcome. The principle behind dose density relates to the Gompertzian model and Norton-Simon hypothesis that smaller tumor grows faster so that the regrowth rate is higher between treatment cycles [17,18], and as tumor shrinks, the regrowth rate increases to make the chemotherapy level capable of initiating regression be insu cient to maintain this regression and produce cure, indicating the regression rate may be overcome by switching to alternative cytotoxic therapy [19].On the contrary, the left four trials [8,[11][12][13]did not indicate any signi cant better survival in sequential regimens than that in concurrent treatment. Given these trials'patients assigned to the concurrent treatment were administrated higher cumulative dosethanBig02-98 [10] and NSABP-30 [9], it may be inferredthatperhaps once the threshold of total dose is surpassed, higher cumulative doses do not add to e cacy.
Accoding to the different choice of anthracyclines in node-positive patients,we conducted a further subanalysis, showingthat patientsreceived doxorubicin, but not epirubicin,hadbetter DFS and OS in sequential treatment.It may be related to that the heart toxicity of epirubicin is lower than doxorubicin, thus patients in both groups can receive optimal dose intensity of epirubicin during the trials [20].The toxicity response during therapy often aggravates the body burden and dampens the patients' medical compliance. Our analysis found thatthe incidences of adverse events such as febrile neutropenia, anemia, fatigue and diarrhea were the similar for the two regimens, partially due to the more often administration of G-CSF in the concurrent treatment.However,neuropathy occuredmore in the sequential regimen which may related to a higher cumulative dose and longer treatment.
Some disadvantages of this meta-analysis should be noted. Firstly, the number of included studies is small. Secondly, heterogeneity, which may affect the result, exists in several trials. HE 10/00 trial [13]included patients with pathological stage T4, while HORG trial [11]focused on patients with early breast cancer as well as node-negative and high risk. Besides, the choice of anthracyclines and the cycles of treatment in the 6 trials are different. Thirdly, subgroup analyses of someconfounding factors, like country, races, hormonal receptor status and Her-2 status, could not be performed to explore the in uence of these factors due to insu cient data.

Conclusions
Breast cancer patients with positive-node and patients who are given doxorubicin, especially for those want fewer cycles of chemotherapy,should be recommended with the sequential regimen. Alternatively, su cient cycles of concomitant regimen may acquire the similar bene t with the sequential regimen does.Concurrent treatment is supposed to be administered with G-CSF prophylactically, and may be a better choice for early breast cancer patients with node-negative sincethey would bene t from the less duration and neuropathy rate. More RCTs with larger sample size should be performed to verify the results of this meta-analysis.
List Of Abbreviations: disease free survival (DFS), overall survival (OS), hazard ratio(HR),risk radio (RR),con dence intervals (CIs),weighted mean difference (WMD)           Figure 5B.The sub-analysis of node status effect inOS between sequential and concurrent regimens.   Figure 6B. The sub-analysis of anthracycline effect in OS between sequential and concurrent regimens.   Funnel plot based on the risk radio(RR) of DFS.