Primary systemic therapy in HER2-positive operable breast cancer using trastuzumab and chemotherapy: efficacy data, cardiotoxicity and long-term follow-up in 142 patients diagnosed from 2005 to 2016 at a single institution

Introduction

Neoadjuvant therapy (NT) is the standard of care for locally advanced and inflammatory breast cancer.^1–4

It is now known that it offers similar benefits like adjuvant therapy in terms of disease-free survival (DFS) and overall survival (OS),^5,6 and so NT is currently implemented for operable disease.

Currently, NT is generally used to improve surgical options, to determine the response to therapy, and it is expected to produce long-term benefits.

Aggressive breast cancer subtypes benefit the most from primary systemic therapy: these include human epidermal growth factor receptor 2 (HER2)-positive and triple-negative tumors.⁷

In HER2-positive tumors, a combination of taxanes and anthracyclines plus trastuzumab has been the standard treatment.^8–13

Trastuzumab interacts with the extracellular domain of HER2 and inhibits signaling from HER2 homodimers more effectively than from HER2 heterodimers with EGF receptor 1 (HER1) or EGF receptor 3 (HER3). This results in the downregulation of the phosphatidylinositol-3 kinase (PI3K) pathway and cell apoptosis. Trastuzumab can also induce antibody-dependent cellular cytotoxicity.^14–16

Despite the advance in the knowledge of HER2-positive tumors and improvements in treatments, a small percentage of patients still suffer from recurrence and die.

Many mechanisms underlying resistance to anti-HER2 therapies have been studied. They include three major groups. The first group involves the concept of “redundancy”. Examples include the inhibition of the incomplete receptor family by a truncated form of the HER2 receptor (p95-HER2) and the lack of exon 16 in the extracellular domain of the HER2 receptor (D16 isoform).

The second major group involves “reactivation”. Examples include the deregulation of the PI3K pathway because of mutations in PI3K catalytic subunit or reduced levels of phosphatidylinositol-3,4,5-triphosphate 3-phosphatase. The third group involves the concept of “scape”. This involves the use of other pathways that can preexist or be acquired at the time of resistance. An example is the cross talk between the estrogen receptor and the HER2 pathways.

Other mechanisms of resistance to anti-HER2 therapies are being studied and include regulators of cell cycle and apoptosis, the tumor microenvironment and immune system, mucins and various receptors and tyrosine kinases.^17,18

However, combinations of targeted agents represent a way to reduce resistance to trastuzumab.

In recent years, we have observed that dual blockade of the HER2 pathway produces better results with an increase in pathological complete response (pCR) rates. In the Neosphere trial, pertuzumab plus trastuzumab and chemotherapy demonstrated higher pCR rates compared with the trastuzumab or pertuzumab arms, and these pCR rates were associated with better DFS.^19–24

Lapatinib was studied in this context in combination with trastuzumab and chemotherapy in several clinical trials. Although some trials of the combination showed higher pCR rates, they did not demonstrate statistically significant long-term benefits. In addition, lapatinib was associated with a worse toxicity profile.^25–29

It is known that the response to treatment depends on clinical factors such as lower stage at diagnosis (small tumors and few or no metastatic axillary nodes) and biological factors such as negative hormone receptor (HR) status, high ki-67 percentage and grade II–III tumors.^30–32

The association between clinical and pathological response has been studied in the neoadjuvant setting. The best imaging methods, such as ultrasound or magnetic resonance imaging (MRI), to monitor tumor shrinkage during treatment^33–38 and their correlation with pathological response have also been analyzed.³⁹

pCR has been associated with long-term benefits, DFS and OS, in several clinical trials and meta-analyses,^7,40 but controversies exist on this point. Some authors consider pCR a surrogate end point that has yet to demonstrate a real long-term benefit.^41,42

The sequential administration of a taxane and an anthracycline plus trastuzumab provides a significant benefit to patients with a high pCR rate.⁴³ The cardiotoxicity associated with this anthracycline plus trastuzumab combination is a drawback,^44–46 but formulations such as epirubicin or liposomal anthracyclines have reduced this negative impact on heart function.^47,48 Although it is still important to monitor left ventricular ejection fraction (LVEF) during treatment, improved knowledge of long-term cardiotoxicity years after the end of treatment is needed.²¹

We analyzed the efficacy data, cardiotoxicity and long-term follow-up in 142 patients with HER2-positive breast cancer tumors diagnosed from 2005 to 2016 at a single institution who were treated homogenously through sequential administration of a taxane and an anthracycline plus trastuzumab.

Patients and methods

This is a retrospective observational study that included 142 patients with stage I–III HER2-positive breast cancer tumors diagnosed from 2005 to 2016 at a single institution.

The study, as well as all procedures performed in the study, was approved by the ethics committee of the Galician region (Comité Autonómico de Ética de Investigación de Galicia, Spain) in 2015 with the code: SAN-TRA-2015-01, and all the patients who were alive at the time the retrospective study was started provided written informed consent for participation.

The study procedures were carried out in accordance with the 1975 Declaration of Helsinki, as revised in 2000, and Good Clinical Practice guidelines.

Patients

All patients included were ≥18 years of age and had Eastern Cooperative Oncology Group Performance Status of ≤1.

Histological type, tumor grade, ki-67 index, estrogen and progesterone receptor and HER2 status were determined locally using pretreatment core biopsies.

HER2-positive breast cancer was considered if the tumors exhibited threefold overexpression of the HER2 receptor as assessed using immunohistochemical techniques (Herceptest^TM Dako until 2013 and Roche until 2016) or a threefold overexpression of the HER2 gene as assessed using fluorescent (until 2013) or silver (2013–2016) in situ hybridization (in the same laboratory) in accordance with 2007 and 2013 American Society of Clinical Oncology/College of American Pathologist guidelines.^49,50

An ultrasound-guided fine-needle puncture aspiration was also performed on suspected malignant axillary lymph nodes at diagnosis.

The tumor site was marked using a stainless steel marker placed using ultrasound guidance in the majority of patients. Multicentric or inflammatory tumors were not marked because of the indication for mastectomy despite the response to treatment.

From 2005 to 2012, a sentinel lymph node biopsy (SLNB) was performed prior to treatment in patients with clinically negative axilla, and from 2012 to 2016 this procedure was performed after treatment.^51,52

At diagnosis, patients were free from cardiovascular disease and demonstrated adequate cardiac function with an LVEF >50%, as measured using echocardiography.

This echocardiography was repeated after three to four cycles, at the end of chemotherapy and during the follow-up period, at least 6 months after the end of adjuvant trastuzumab.

Patients also had adequate hematological, renal and hepatic function.

The different treatment regimens administered are shown in Figure 1. The vast majority of patients received a total of eight cycles consisting of a sequence of anthracyclines and taxanes with trastuzumab.

Figure 1 Types of chemotherapy. Notes: *Chemotherapy doses. Paclitaxel: 80 mg/m2, weekly ×12 doses. FEC: 5-fluorouracil: 600 mg/m2/epirubicin: 75 mg/m2/cyclophosphamide: 600 mg/m2 every 3 weeks × four cycles. Myocet: 60 mg/m2/cyclophosphamide: 600 mg/m2/every 3 weeks × four cycles. T: 8 mg/kg IV loading dose followed by 6 mg/kg IV every 3 weeks (a total of 12 months, including in the neoadjuvant and adjuvant setting). Abbreviations: FEC, 5-fluorouracil–epirubicin–cyclophosphamide; IV, intravenous; T, trastuzumab.

Physical examinations were performed every 3 weeks during chemotherapy treatment. Mammograms, ultrasound and MRI were performed before and after neoadjuvant treatment.

The clinical response (CR) was measured through physical examination and MRI in accordance with the response evaluation criteria in solid tumors.^53,54

Patients underwent surgery between 3 and 5 weeks from the end of chemotherapy. There was an increase in conservative breast surgery in patients that were candidates for mastectomy at diagnosis.

pCR was defined as the total absence of invasive tumor in both breast and axillary nodes (ypT0/is ypN0).

The pathological response was measured in accordance with the Miller and Payne system in most patients.⁵⁵

We used the revised American Joint Committee on Cancer TNM system in patients included in the first 2 years of the study.⁵⁶

This pathological response was correlated with clinical and biological factors (tumor size, axillary nodes, HR status and ki-67 index).

All patients treated using conservative breast surgery received whole-breast irradiation at a standard dose. Some patients with T3 tumors at diagnosis were also irradiated after mastectomy. Regional nodal irradiation of the supraclavicular fossa-axillary apex was used in patients with clinical stage III disease, in patients with four or more positive lymph nodes and in selected patients with one to three positive lymph nodes.^57,58

After completion of systemic and local therapy, patients with HR-positive tumors received tamoxifen or an aromatase inhibitor if the patient was menopausal.

We report DFS (defined as the time from surgery to the first documented disease progression) and OS (time from surgery to death).

Statistical analyses

We performed a descriptive analysis for all variables. Continuous variables were reported using the median as the central value and the SD. For dichotomous or categorical variables, absolute numbers and percentages were computed. The chi-squared two-tailed test was used for comparative analyses between categorical variables.

We estimated DFS and OS rates for each group using the Kaplan–Meier method. A comparison of survival curves was performed using the log-rank test. Differences in survival between groups were compared using the Cox regression test. All statistical tests were two sided, and a significance level of 0.05 was applied.

Results

A total of 142 patients with stage I–III HER2-positive breast cancer tumors, who were candidates for primary systemic therapy and were diagnosed from 2005 to 2016 at our institution, were included in the study. The pretreatment characteristics of the patients are listed in Table 1.

Table 1 Patient characteristics Note: aOne patient had a nonmeasurable lobular tumor, and another had an occult carcinoma. Abbreviations: cT, clinical tumor size; FISH, fluorescent in situ hybridization; HR, hormone receptor; IHC, Immunohistochemistry; SISH, silver in situ hybridization.

The median patient age was 49 (30–79) years, with stage I, II or III breast cancer at diagnosis in 4%, 69% and 27%, respectively. A total of 10% of patients had inflammatory breast cancer, 43% of tumors were HR negative and 62% were grade III, while 90% of tumors were confirmed to be HER2 positive through immunohistochemistry (threefold increase in protein expression) and the rest through fluorescent in situ hybridization or silver in situ hybridization. A total of 84% of patients had an indication for mastectomy at diagnosis.

A total of 98% of patients completed the planned cycles of chemotherapy. The remaining 2% (three patients) could not complete chemotherapy because of hepatotoxicity in one patient, sustained grade III asthenia and grade II neutropenia in an elderly patient and a massive pulmonary thromboembolism in the third patient after four cycles of chemotherapy.

Clinical response

The CR was assessed through mammography, ultrasound imaging and MRI before and after systemic therapy and immediately before surgery in most patients.

In the first years of the study, breast MRI was not a routine imaging technique, so it was not performed in the first 18 patients.

The CR data are listed in Table 2.

Table 2 Complete response Notes: aMRI was performed in 124 patients. Not evaluable, nonmeasurable disease or not performed. Abbreviations: CR, complete response; MRI, magnetic resonance imaging; PD, progressive disease; PR, partial response; SD, stable disease.

A total of 49% and 63% of patients demonstrated a clinical complete response, as measured through ultrasound and MRI, respectively.

Pathological response

The pCR rate, defined as the total absence of invasive tumor in both breast and axillary nodes (ypT0/is ypN0), was 52%. The pCR rates in breast, breast and axilla and in different subgroups are summarized in Tables 3 and 4.

Table 3 pCR in breast and breast/axilla Abbreviation: pCR, pathological complete response.

Table 4 pCR by subgroups Abbreviations: 5-FEC, 5-fluorouracil–epirubicin–cyclophosphamide; HR, hormone receptor; Pac, paclitaxel; pCR, pathological complete response; T, trastuzumab.

The pCR rate was higher in ductal (53%) than in lobular (14%) cancer, in HR-negative (64%) than in HR-positive (41%) cancer, in grade III (53%) than in grade I–II (45%) cancer and in tumors with a ki-67 value >20 (85%) than in those with a ki-67 value <20 (15%).

A total of 61% and 68% of patients with CR, as assessed using ultrasound and MRI, respectively, also demonstrated pCR.

pCR was higher in patients treated using paclitaxel/trastuzumab (PT) followed by Myocet/cyclophosphamide/trastuzumab (54%) than those treated using PT followed by fluorouracil/epirubicin/cyclophosphamide/trastuzumab (38%), but the numbers of patients assigned to each group were too low to result in statistically significant differences.

Surgery

At diagnosis, 84% of patients were indicated for mastectomy. After treatment, tumorectomy was performed in 66%.

Axillary dissection, SLNB and no axillary procedure were performed in 69%, 22% and 9% of patients, respectively. Those patients with a negative SLNB before treatment did not undergo an axillary procedure.

Long-term efficacy data

At the time of the analysis in March 2018, and with a median follow-up of 55 months, 27 patients suffered from breast cancer recurrence and 15 patients died as a result of any cause.

DFS and OS curves are shown in Figures 2 and 3, respectively. We were able to demonstrate an association between pCR and better DFS with statistical significance (P=0.19) and a trend toward improved OS (P=0.068; Figures 4 and 5).

Figure 2 DFS assessed using the Kaplan–Meier method. Abbreviation: DFS, disease-free survival.

Figure 3 OS assessed using the Kaplan–Meier method. Abbreviation: OS, overall survival.

Figure 4 DFS based on pCR. Abbreviations: DFS, disease-free survival; pCR, pathological complete response.

Figure 5 OS based on pCR. Abbreviations: OS, overall survival; pCR, pathological complete response.

Cardiotoxicity

Because of the potential cardiotoxicity associated with anthracyclines and trastuzumab, knowledge of cardiovascular risk factors and patient monitoring were very important during the study.

Age at diagnosis, body mass index (BMI), arterial hypertension, dyslipidemia, preexisting cardiovascular disease and previous radiotherapy are recognized as risk factors for heart disease in breast cancer patients treated using anthracyclines and trastuzumab.^59–65

The risk factors for developing a cardiac event in the current cohort of patients are listed in Table 5.

Table 5 Risk factors for cardiac events Note: aBMI: 25–30, overweight; >30, obese. Abbreviation: BMI, body mass index.

At diagnosis, all patients had adequate cardiac function with an LVEF of >50%, as measured using echocardiography.

The echocardiography was repeated after chemotherapy treatment and during follow-up at least 6–12 months after the end of adjuvant trastuzumab in 70% of patients.

At the end of chemotherapy treatment, five patients suffered a decline in LVEF <50% (3.5% of patients). The cardiovascular risk factors for these patients are listed in Table 6.

Table 6 Cardiovascular risk factors in patients who suffered a decline in LVEF <50% Abbreviations: BMI, body mass index; LVEF, left ventricular ejection fraction.

Of these patients, four did not experience cardiac symptoms and demonstrated a rapid recovery after temporarily stopping trastuzumab. One did not receive adjuvant trastuzumab. Three received left breast radiotherapy and two had a history of high blood pressure.

The fifth patient who suffered a decline in LVEF below 50% did not receive adjuvant trastuzumab and developed severe ventricular dysfunction over subsequent years.

This patient had a high BMI and received left breast radiotherapy, which are risk factors for heart disease.

LVEF at baseline, end of chemotherapy and beyond 6 months from the end of trastuzumab treatment is shown in Figure 6.

Figure 6 Basal LVEF at the end of chemotherapy and follow-up. Abbreviation: LVEF, left ventricular ejection fraction.

Discussion

Although clear clinical and preclinical evidence for dual blockade of the HER2 pathway in neoadjuvant treatment of HER2-positive breast cancer has been reported and this has become a standard approach in combination with chemotherapy, some issues remain controversial. Do all patients benefit from the addition of the second biological inhibitor to their chemotherapy regimen, and what is the role of anthracyclines and cardiotoxicity?

Considering that we retrospectively analyzed a homogeneous population treated using a taxane and anthracycline concomitantly with trastuzumab and all treatment was administered before surgery, the median pCR (total absence of invasive tumor in both breast and axillary nodes) achieved in our cohort was high (52%) and is comparable to other treatment series employing a similar sequence. In a previous study, Buzdar et al¹¹ used sequential 5-fluorouracil–epirubicin–cyclophosphamide (FEC) and paclitaxel with trastuzumab and achieved a higher pCR (56%), but only evaluated pCR in the breast.

The median pCR achieved in studies employing dual blockade of the HER2 pathway ranges from 45% to 62%. In the most important of these studies (Neosphere and Tryphaena), only pCR in the breast was evaluated.

It is known that the combination of anthracyclines and trastuzumab is very active, but it can increase cardiotoxicity. There are anthracyclines such as epirubicin or liposomal formulations that can reduce this toxicity.

A Phase III trial reported that adding trastuzumab to epirubicin does not improve efficacy in terms of pCR in a sequence with taxane and trastuzumab vs epirubicin alone using the same sequence. However, long-term efficacy and cardiotoxicity data are needed to draw robust conclusions.¹⁰

In the current study, 37 patients were treated with epirubicin and 85 with liposomal doxorubicin (Myocet^®; Teva B.V, Haarlem, the Netherlands), achieving a higher pCR rate in the Myocet group (38% and 51%, respectively). The number of patients assigned to each group was too low to produce statistically significant differences.

These rates are comparable to those in other published series using FEC or classic anthracyclines. There is little evidence to support the use of liposomal anthracyclines in the neoadjuvant setting. Most published series uses concomitant administration of chemotherapeutics instead of sequential administration and a higher number of cycles.^48,66–68

We identified three biological factors associated with a better response to therapy: HR-negative status, ki-67 >20% and grade III breast cancer.

The high pCR achieved in the HR-negative patients vs the HR-positive patients was also seen in previous clinical trials in the HER2 neoadjuvant setting,^19,26,69 and this could be explained by the cross talk between the HER2 and endocrine pathway conferring resistance to agents targeting either pathway.

Many studies have demonstrated the prognostic and predictive value of ki-67, whereby it is used to identify patients who will benefit most from systemic therapy. These studies used different methods for scoring this proliferation antigen and included a heterogeneous population with different biological subtypes.^70,71

A 20% cutoff point for the ki-67 index appears to be a statistically significant prognostic factor in luminal B HER2-negative tumors. The median value of ki-67 is usually higher in triple-negative and HER2-positive tumors. Median ki-67 values of 35%–40% in HER2-positive and 50% in triple-negative breast cancer have been previously reported.⁷²

In the current study, we examined three different cutoff points for the ki-67 index and their relationship with pCR, DFS and OS.

Tumors with ki-67 >20% (especially those >35%) achieved higher pCR rates, but no group was correlated with long-term benefits.

The correlation between histological grade and prognosis has been confirmed in multiple reports and currently helps clinicians to make treatment decisions.^73–78 Its value as an independent factor to predict the response to NT is unclear.^30,31 In the current series, grade III tumors achieved a higher pCR rate compared with grade I–II tumors.

There was a high rate of indication for mastectomy at diagnosis in the current series. This could be explained by the incidence of T3 and T4 tumors and the relationship between breast/tumor size in T2 tumors.

After systemic treatment, the rates of breast conservation were also high and greater than in other previously reported series.^79–81 We attributed this to the high pCR achieved in this selected HER2 population.

The potential for an increase in local recurrence after NT followed by breast conservation was analyzed in several studies and meta-analyses.^5,82 The MD Anderson Prognostic Index concludes that the local recurrence rate could depend on other biological factors such as clinical N2 or N3 disease, lymphovascular space invasion, a multifocal pattern of residual disease and a residual pathological primary tumor >2 cm, rather than the timing of chemotherapy delivery.^83,84

Our locoregional recurrence rate of 3.9% is low at the time of data cutoff.

A high percentage (61%–68%) of tumors that achieved CR, assessed using ultrasound and MRI, also demonstrated pCR. MRI has been reported as superior to ultrasound and mammography in the assessment of tumor extent and is highly sensitive in identifying residual disease following neoadjuvant treatment.^85,86 We perceived a slight superiority of MRI in the current series.

pCR in HER2-positive breast cancer is associated with a substantially longer time to recurrence and death, as reported in a meta-analysis published by Broglio et al,⁴⁰ which included a total of 5,500 HER2-positive breast cancer patients.

We demonstrated an association between pCR and improved DFS (P=0.19) in the current patients and a trend toward improved OS (P=0.068). This absence of a statistically significant benefit in OS could be explained by the low number of deaths at the time of analyses and to improvements in treatments for metastatic disease. None of the patients in the current series received pertuzumab in the neoadjuvant setting.

Concomitant administration of trastuzumab and classic anthracyclines is cardiotoxic and not permitted in clinical use.

In recent years, the incidence of congestive heart failure associated with trastuzumab and anthracyclines has become very low, since close monitoring of cardiac function and liposomal and less cardiotoxic anthracyclines have been used.^11,43,48

We used two-dimensional echocardiography to monitor trastuzumab-related cardiotoxicity following the current clinical guidelines. This is a readily available cardiac imaging modality with low cost and is radiation free. However, the current knowledge indicates that this technique does not accurately predict the development of cardiotoxicity. New imaging modalities can provide more information in the early stages and can quantify myocardial deformation as a marker of contractility. These new echocardiographic techniques, such as global longitudinal strain, can provide information that is predictive of cardiac dysfunction.^87,88

Cardiac biomarkers, such as troponins and amino-terminal fragment of brain natriuretic peptide, are also a useful tool to monitor cardiotoxicity. They have been studied as early predictors of cardiac damage in patients receiving anthracyclines and anti-HER2 therapy with disparate results.^89,90

After a long follow-up period, our data showed a low incidence of cardiac events: 2.95% of patients demonstrated an asymptomatic decrease in LVEF and 0.64% demonstrated symptomatic ventricular dysfunction. Both cardiac events were related to other cardiovascular risk factors such as high BMI or high blood pressure and left breast radiotherapy.

This low incidence of cardiac events did not allow us to achieve statistically significant differences between the cardiotoxicity profiles of the chemotherapy treatments. The five patients who suffered a decline in LVEF <50% at the end of chemotherapy treatment had received concomitant anthracyclines and trastuzumab instead of the sequential treatments.

Although the incidence of cardiotoxicity was low, it is desirable to avoid it through better selection of patients and the correction of cardiovascular risk factors (high BMI, arterial hypertension, dyslipidemia) from the beginning, not only through diet and exercise but also using medication. The early administration of angiotensin–convertin–enzyme inhibitors (enalapril type) or beta-blockers (carvedilol or bisoprolol type) or a combination of both has produced improvements in cardiac function in breast cancer patients treated using anthracyclines. This highlights the need for collaboration between cardiologists and oncologists from the beginning of treatment.^91–93

Conclusion

The sequence of a taxane and a less cardiotoxic anthracycline concomitant to trastuzumab was effective in the HER2 neoadjuvant setting with high pCR and conservative breast surgery rates. Grade III and HR-negative tumors demonstrated the greatest benefit.

We observed a good correlation between the clinical complete response, as measured using ultrasound and MRI, and pCR.

We were able to associate pCR with improved DFS. Although there was a trend toward improved OS, it was not statistically significant.

The treatment was safe with an excellent long-term cardiotoxicity profile.

Acknowledgments

We would like to thank all the patients who participated in the study and the following people: Javier Prato, Aurea Molina, Joaquin Mosquera, Cristina Reboredo, Begoña Graña, María Quindós (Medical Oncology Department, A Coruña University Hospital), Manuel Juaneda (Surgery Department, Breast Unit, A Coruña University Hospital), Alberto Bouzón, Carmen Conde (Gynecology Department, Breast Unit, A Coruña University Hospital), Carlota Diaz (Gynecology Department, Breast Unit, A Coruña University Hospital), Carmen Cereijo (oncology nurse, Breast Unit, A Coruña University Hospital). This study did not receive any specific grants from funding agencies in the public, commercial or nonprofit sectors.

Disclosure

The authors report no conflicts of interest in this work.

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