Pertuzumab for the treatment of breast cancer: a safety review

Cardiovascular Health Considerations for Primary Care Physicians Treating Breast Cancer Survivors

Breast cancer (BC) survivors are at increased risk for cardiovascular disease (CVD) and require their primary care physicians to manage their long-term general medical care, including cardiovascular (CV) health. Yet, evidence exists that some primary care physicians possess insufficient knowledge about survivorship care. With the goal of bridging these knowledge gaps, a PubMed review was conducted from July 7, 2020, through October 2, 2020, with an updated PubMed review from January 3, 2024, through April 28, 2024, focusing on CV health considerations in the primary care of BC survivors. Search terms included variations of "breast cancer survivors" and "cardiovascular." In total, 152 publications were included. Breasts cancer survivors may have increased CVD risk because some anticancer therapies are cardiotoxic and risk factors for BC often also increase the risk for CVD. Multiple risk factors overlap for BC and CVD such as older age, Western diet, early menarche, physical inactivity, high body mass index, and smoking. In this review, results are summarized from studies that report the presence of CV risk factors and CVD in BC survivors. Also described are the CV effects of BC therapies (chemotherapy, hormonal agents, targeted therapies, and radiotherapy) and the type of CV evaluation (cardiac imaging and measurement of biomarkers) that these patients may need. Primary care physicians have an important role in managing the CV health of BC survivors from preventing, assessing, and managing CV risk factors to referring patients to appropriate specialists when needed.

A disproportionality analysis of adverse events associated to pertuzumab in the FDA Adverse Event Reporting System (FAERS)

BACKGROUND

Pertuzumab is widely used for the treatment of HER2 + breast cancer. But its safety in the real world should be continuously monitored. So, we evaluated the safety of pertuzumab by pharmacovigilance analyze based on related adverse events (AEs) from the FDA Adverse Event Reporting System (FAERS) and find whether potential or uncertain adverse events were present.

METHODS

In disproportionality analysis, four algorithms were employed to detect the signals of pertuzumab from the FAERS between 2012 and 2022. In addition, we also used MYSQL 8.0, Navicat Premium 15, and Microsoft EXCEL 2019 to analyze the potential and high-ROR (reporting odds ratio) signals of pertuzumab. We also collected the onset times of pertuzumab-associated AEs.

RESULTS

From January 2012 to December 2022, there are 39,190,598 AEs reported from the FAERS database, of which 14,707 AEs listed pertuzumab as the 'primary suspected (PS)' drug. A total of 115 (46 potential) significant disproportionality preferred terms (PTs) conforming to the four algorithms were retained. Finally, we detected that the pertuzumab-induced AEs occurred in 12 organ systems. For pertuzumab, unexpected and significant PTs of AEs were found, including but not limited to below PTs: haematotoxicity, cardiotoxicity, cardiomyopathy, mitral valve incompetence, tachycardia, intestinal perforation, hemorrhoids, erysipelas, dehydration, pneumonitis, skin toxicity, onychomadesis, cyanosis, and circulatory collapse. We found there were 9 strong signals (5 potential safety signals) and 68 medium intensity signals (21 potential safety signals) according to IC025 (information component). The potential strong signals (IC025 > 3.0) were myelosuppression, cardiotoxicity, cardiac dysfunction, ejection fraction decreased, interstitial lung disease, and onychomadesis. Excluding unreported or unreasonable onset time reports, a total of 2016 AEs reported onset time and the median onset time was 117 days (4, 96), as median (Q1, Q3). Notably, most of the all AEs (n = 1133, 56%) and cardiac-related events (n = 405, 53%) all occurred within one month after pertuzumab therapy.

CONCLUSION

Analysis of FAERS data identified pertuzumab-associated AEs, and our findings supported continuous clinical monitoring, pharmacovigilance, and further studies of pertuzumab. A significant association was detected between pertuzumab and some potential adverse events which should be regarded with some care. We have to pay attention to the first month after pertuzumab therapy and prepare emergency measures, especially for the elderly and patients with cardiovascular diseases.

Ebselen oxide and derivatives are new allosteric HER2 inhibitors for HER2-positive cancers

Human epidermal growth factor receptor 2 (ErbB2/HER2) is a tyrosine kinase receptor that is overexpressed in 25% of primary human breast cancers, as well as in multiple other cancers. HER2-targeted therapies improved progression-free and overall survival in patients with HER2+ breast cancers. However, associated resistance mechanisms and toxicity highlight the need for new therapeutic approaches for these cancers. We recently established that, in normal cells, HER2 is stabilized in a catalytically repressed state by direct interaction with members of the ezrin/radixin/moesin (ERM) family. In HER2-overexpressing tumors, the low expression of moesin contributes to the aberrant activation of HER2. Through a screen designed to find moesin-mimicking compounds, we identified ebselen oxide. We show that ebselen oxide, and some derivatives, conferred an efficient allosteric inhibition of overexpressed HER2, as well as mutated and truncated oncogenic forms of HER2, which are resistant to current therapies. Ebselen oxide selectively inhibited anchorage-dependent and -independent proliferation of HER2+ cancer cells and showed a significant benefit in combination with current anti-HER2 therapeutic agents. Finally, ebselen oxide significantly blocked HER2+ breast tumor progression in vivo. Collectively, these data provide evidence that ebselen oxide is a newly identified allosteric inhibitor of HER2 to be considered for therapeutic intervention on HER2+ cancers.

Pertuzumab Charge Variant Analysis and Complementarity-Determining Region Stability Assessment to Deamidation

Pertuzumab is a monoclonal antibody used for the treatment of HER2-positive breast cancer in combination with trastuzumab. Charge variants of trastuzumab have been extensively described in the literature; however, little is known about the charge heterogeneity of pertuzumab. Here, changes in the ion-exchange profile of pertuzumab were evaluated by pH gradient cation-exchange chromatography after stressing it for up to 3 weeks at physiological and elevated pH and 37 °C. Isolated charge variants arising under stress conditions were characterized by peptide mapping. The results of peptide mapping showed that deamidation in the Fc domain and N-terminal pyroglutamate formation in the heavy chain are the main contributors to charge heterogeneity. The heavy chain CDR2, which is the only CDR containing asparagine residues, was quite resistant to deamidation under stress conditions according to peptide mapping results. Using surface plasmon resonance, it was shown that the affinity of pertuzumab for the HER2 target receptor does not change under stress conditions. Peptide mapping analysis of clinical samples showed an average of 2-3% deamidation in the heavy chain CDR2, 20-25% deamidation in the Fc domain, and 10-15% N-terminal pyroglutamate formation in the heavy chain. These findings suggest that in vitro stress studies are able to predict in vivo modifications.

Rare ocular toxicity induced by pertuzumab/QL1209 in healthy chinese subjects: case reports and whole-exome sequencing analysis

Pertuzumab is a recombinant anti-HER2 humanized monoclonal antibody widely used for the adjuvant treatment of HER2-positive breast cancer. Its safety is well established with the most common adverse effects being diarrhea and rash. To our knowledge, severe pertuzumab-induced ocular adverse events have never been reported. Herein, we describe several cases of pertuzumab/QL1209 (pertuzumab biosimilar)-induced blurred vision in healthy Chinese male subjects after a single injection of 420 mg pertuzumab/QL1209. Persistent optic nerve damage and vision loss occurred in the most severe case even after ophthalmic treatment. We conducted whole-exome sequencing (WES) of DNA samples from 5 cases and 13 controls to analyze the potential genetic factors and identified some associated variants (rs80303690 in RBM24, rs117375173 in CASR, rs1805097 in IRS2, and rs1227049 in CDH23). Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene Ontology (GO) terms gene enrichment analyses were carried out for differentially expressed genes clustered in the PI3K/AKT/mTOR and Ras/Raf/MAPK signaling pathways, which were exactly activated by HER2 phosphorylation. In summary, this is the first report describing the occurrence of ocular toxicity induced by pertuzumab in the Chinese population and exploring the possible genetic mechanisms. These findings could provide evidence for clinicians to raise concerns about the risk of ocular toxicity with the clinical use of pertuzumab.

Updated Results of TBCRC026: Phase II Trial Correlating Standardized Uptake Value With Pathological Complete Response to Pertuzumab and Trastuzumab in Breast Cancer

PURPOSE

Predictive biomarkers to identify patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer who may benefit from targeted therapy alone are required. We hypothesized that early measurements of tumor maximum standardized uptake value corrected for lean body mass (SULmax) on 18F-labeled fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) would predict pathologic complete response (pCR) to pertuzumab and trastuzumab (PT).

PATIENTS AND METHODS

Patients with stage II or III, estrogen receptor-negative, HER2-positive breast cancer received four cycles of neoadjuvant PT. 18F-labeled fluorodeoxyglucose positron emission tomography-computed tomography was performed at baseline and 15 days after PT initiation (C1D15). Eighty evaluable patients were required to test the null hypothesis that the area under the curve of percent change in SULmax by C1D15 predicting pCR is ≤ 0.65, with a one-sided type I error rate of 10%.

RESULTS

Eighty-eight women were enrolled (83 evaluable), and 85% (75 of 88) completed all four cycles of PT. pCR after PT alone was 22%. Receiver operator characteristic analysis of percent change in SULmax by C1D15 yielded an area under the curve of 0.72 (80% CI, 0.64 to 0.80; one-sided P = .12), which did not reject the null hypothesis. However, between patients who obtained pCR and who did not, a significant difference in median percent reduction in SULmax by C1D15 was observed (63.8% v 41.8%; P = .004) and SULmax reduction ≥ 40% was more prevalent (83% v 52%; P = .03; positive predictive value, 31%). Participants not obtaining a 40% reduction in SULmax by C1D15 were unlikely to obtain pCR (negative predictive value, 91%).

CONCLUSION

Although the primary objective was not met, early changes in SULmax predict response to PT in estrogen receptor-negative and HER2-positive breast cancer. Once optimized, this quantitative imaging strategy may facilitate tailoring of therapy in this setting.

Association between pertuzumab-associated diarrhoea and rash and survival outcomes in patients with HER2-positive metastatic breast cancer: Exploratory analysis from the CLEOPATRA trial

BACKGROUND

Skin rash and diarrhoea are known side-effects of pertuzumab. Studies with other anti-HER2 agents suggested that adverse events correlate with patient outcomes. In this exploratory cohort of patients with metastatic HER2-positive breast cancer included in the CLEOPATRA trial we evaluated the value of rash and diarrhoea as prognostic markers and as predictors of pertuzumab benefit.

METHODS

This is a retrospective analysis of the multicenter, prospective, randomised CLEOPATRA trial. We defined two analytic cohorts: cohort 1 (C1) included patients from treatment initiation, and cohort 2 (C2) included patients after discontinuation of docetaxel. A landmark analysis was introduced to deal with immortal-time bias. Study endpoints were progression-free survival (PFS) and overall survival (OS). Univariable and multivariable Cox proportional hazards models were used.

RESULTS

Of the 808 patients and after application of the landmark analysis, C1 and C2 included 777 and 518 patients, respectively. In C1, rash occurred in 271 patients (34.9%) and diarrhoea in 470 (60.5%). Rash was prognostic for PFS and OS (C1: adjusted hazard ratio [aHR] = 0.66 [95% CI = 0.48-0.91], p = 0.010]; C2: aHR 0.52 [95% CI = 0.30-0.89], p = 0.018) in both cohorts, while diarrhoea was only prognostic for PFS in cohort 2 (aHR = 0.65 [95% CI = 0.46-0.91], p = 0.011). Rash and diarrhoea were not predictive of pertuzumab benefit (in terms of PFS/OS) in the two cohorts.

CONCLUSIONS

In patients treated with pertuzumab, trastuzumab, and docetaxel, rash is prognostic whenever it occurs during treatment, while diarrhoea only has prognostic value when occurring after docetaxel discontinuation. However, neither rash nor diarrhoea predict pertuzumab benefit.

Nanomedicine: A Promising Avenue for the Development of Effective Therapy for Breast Cancer

PURPOSE

Breast cancer is the most probable cancer among women. However, the available treatment is based on targeting different stages of breast cancer viz., radiation therapy, hormonal therapy, chemotherapy, and surgical interventions, which have some limitations. The available chemotherapeutics are associated with problems like low solubility, low permeability, high first-pass metabolism, and P-glycoprotein efflux. Hence, the aforementioned restrictions lead to ineffective treatment. Multiple chemotherapeutics can also cause resistance in tumors. So, the purpose is to develop an effective therapeutic regimen for the treatment of breast cancer by applying a nanomedicinal approach.

METHODS

This review has been conducted on a systematic search strategy, based on relevant literature available on Pub Med, MedlinePlus, Google Scholar, and Sciencedirect up to November 2019 using keywords present in abstract and title of the review. As per our inclusion and exclusion criteria, 226 articles were screened. Among 226, a total of 40 articles were selected for this review.

RESULTS

The significant findings with the currently available treatment is that the drug, besides its distribution to the target-specific site, also distributes to healthy cells, which results in severe side effects. Moreover, the drug is less bioavailable at the site of action; therefore, to overcome this, a high dose is required, which again causes side effects and lower the benefits. Nanomedicinal approaches give an alternative approach to avoid the associated problems of available chemotherapeutics treatment of breast cancer.

CONCLUSION

The nanomedicinal strategies are useful over the conventional treatment of breast cancer and deliver a target-specific drug-using different novel drug delivery approaches.

TBCRC026: Phase II Trial Correlating Standardized Uptake Value With Pathologic Complete Response to Pertuzumab and Trastuzumab in Breast Cancer

PURPOSE

Predictive biomarkers to identify patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer who may benefit from targeted therapy alone are required. We hypothesized that early measurements of tumor maximum standardized uptake values corrected for lean body mass (SULmax) on [¹⁸F]fluorodeoxyglucose positron emission tomography/computed tomography would predict pathologic complete response (pCR) to neoadjuvant pertuzumab and trastuzumab (PT).

PATIENTS AND METHODS

Patients with stage II/III, estrogen receptor-negative, HER2-positive breast cancer received four cycles of neoadjuvant PT. [¹⁸F]Fluorodeoxyglucose positron emission tomography/computed tomography was performed at baseline and 15 days after PT initiation (C1D15). Eighty evaluable patients were required to test the null hypothesis that the area under the curve of percentage of change in SULmax by C1D15 predicting pCR is less than or equal to 0.65, with a one-sided type I error rate of 10%.

RESULTS

Eighty-eight women were enrolled (83 evaluable), and 85% (75 of 88) completed all four cycles of PT. pCR after PT alone was 34%. Receiver operating characteristic analysis yielded an area under the curve of 0.76 (90% CI, 0.67 to 0.85), which rejected the null hypothesis. Between patients who obtained pCR versus not, a significant difference in median percent reduction in SULmax by C1D15 was observed (63.8% v 33.5%; P < .001), an SULmax reduction greater than or equal to 40% was more prevalent (86% v 46%; P < .001; negative predictive value, 88%; positive predictive value, 49%), and a significant difference in median C1D15 SULmax (1.6 v 3.9; P < .001) and higher proportion of C1D15 SULmax less than or equal to 3 (93% v 38%; P < .001; negative predictive value, 94%; positive predictive value, 55%) were observed.

CONCLUSION

Early changes in SULmax predict response to four cycles of PT in estrogen receptor-negative, HER2-positive breast cancer. Once optimized, this quantitative imaging strategy may facilitate a more tailored approach to therapy in this setting.

Trastuzumab induces PUMA-dependent apoptosis and inhibits tumor growth in gastric cancer

Gastric cancer (GC) is one of the most prevalent cancers worldwide. Trastuzumab has been approved for the treatment of metastatic GC, gastroesophageal junction cancer, and breast cancer. However, the mechanisms involved in trastuzumab-induced GC cell apoptosis remain largely unknown. In this study, we investigated the underlying mechanisms of trastuzumab-mediated suppression of GC cell growth both in vitro and in vivo. We found that trastuzumab treatment induces p53 upregulated modulator of apoptosis (PUMA) expression in GC cells, through the NF-κB pathway following AKT inhibition and glycogen synthase kinase 3β (GSK3β) activation. We also observed that PUMA was necessary for trastuzumab-induced apoptosis in GC cells. Moreover, PUMA deficiency suppressed apoptosis and the antitumor effect of trastuzumab in xenograft models. Finally, computerized tomography (CT) and immunohistochemistry results showed that patients with increased activation of PUMA were more sensitive to trastuzumab treatment than those with low PUMA expression. These results indicate that trastuzumab induces PUMA-dependent apoptosis and inhibits tumor growth in GC, suggesting that PUMA plays a critical role in mediating the antitumor effects of trastuzumab in GC. PUMA induction may be used as a marker of trastuzumab sensitivity.

Safety Assessment of Neoadjuvant Pertuzumab Combined with Trastuzumab in Nonmetastatic HER2-Positive Breast Cancer in Postmenopausal Elderly Women of South Asia

Aim

To evaluate the safety issues and adverse effects of using TCHP regimen (docetaxel, carboplatin, trastuzumab, and pertuzumab) versus TCP regimen (docetaxel, carboplatin, and trastuzumab) in older postmenopausal women with nonmetastatic HER2-positive breast cancer. HER2 overexpressed in 20–25% of breast cancer signals an aggressive form of breast cancer and is treated with trastuzumab and pertuzumab.

Methods

The patient record database was accessed to identify all postmenopausal women in the Punjab Care hospital who were above 65 years old, with stages 1–3 HER2-positive breast cancer and treated with neoadjuvant TCHP and neoadjuvant TCP from 2013 till 2016.

Results

In TCH-P group and TCH group, mild fatigue (34% versus 36%) and diarrhea (48% versus 49%) were most common toxicities. Fever in TCH-P group and TCH group (12% versus 13%) was common. Anorexia affected 21% and 16% of patients receiving TCH and TCHP regimen, respectively. Febrile neutropenia was higher in TCH-P group 13% (3/23) versus 4.5% (1/22) in TCH group. Also 27.2% (6/22) of TCH-P group was hospitalized for treatment related toxicities versus 21.7% (5/23) of TCH group.

Conclusion

Comparing neoadjuvant TCP and neoadjuvant TCH-P showed TCH-P regimen had an acceptable toxicity profile. Severe cardiac dysfunction was not observed. Using TCH-P regimen can be considered as relatively safe therapeutic option for elderly postmenopausal women with nonmetastatic HER2-positive breast cancer.

Cardiotoxic effects of the novel approved anti-ErbB2 agents and reverse cardioprotective effects of ranolazine

Purpose

Pertuzumab, a novel anti-epidermal growth factor receptor 2 humanized monoclonal antibody, and trastuzumab-emtansine (TDM1), a novel antibody-drug conjugate made up of trastuzumab covalently linked to the highly potent microtubule inhibitory agent DM1, have been recently approved by the US Food and Drug Administration for increasing the efficiency and safety of breast cancer therapy with trastuzumab. We investigated for the first time the potential cardiotoxic effects of pertuzumab and TDM1, which are not yet fully elucidated, and we tested whether ranolazine could blunt their cardiotoxicity.

Methods

The cardiotoxic effects were tested in vitro on rat cardiomyoblasts, human fetal cardiomyocytes, adult-like cardiomyocytes, and in vivo on a mouse model.

Results

All the treated cardiac cell lines were significantly affected by treatment with the tested drugs. Surprisingly, TDM1 showed stronger inhibitory effects on cardiac cells with respect to trastuzumab and pertuzumab by more significantly reducing the cell viability and by changing the morphology of these cells. TDM1 also affected the beating phenotype of adult-like cardiomyocytes in vitro and reduced fractional shortening and ejection fraction in vivo in a mouse model. We also found that ranolazine attenuated not only the cardiotoxic side effects of trastuzumab but also those of pertuzumab and TDM1, when used in combinatorial treatments both in vitro and in vivo, as demonstrated by the recovery of fractional shortening and ejection fraction values in mice pretreated with TDM1.

Conclusion

We demonstrated that it is possible to predict the eventual cardiotoxic effects of novel approved anticancer drugs early by using in vitro and in vivo approaches, which can also be useful to screen in advance the cardioprotective agents, so as to avoid the onset of unwanted cardiotoxic side effects.

Monoclonal antibody-based therapeutics, targeting the epidermal growth factor receptor family: from herceptin to Pan HER

Objectives

Monoclonal antibody-based of cancer therapy has been considered as one of the most successful therapeutic strategies for both haematologic malignancies and solid tumours in the last two decades. Epidermal growth factor receptor (EGFR) family signalling pathways play a key role in the regulation of cell proliferation, survival and differentiation. Hence, anti-EGFR family mAbs is one of the most promising approaches in cancer therapy.

Key findings

Here, recent advances in anti-EGFR mAb including approved or successfully tested in preclinical and clinical studies have been reviewed. Although we focus on monoclonal antibodies against the EGF receptor, but the mechanisms underlying the effects of EGFR-specific mAb in cancer therapy, to some extend the resistance to existing anti-EGFR therapies and some therapeutic strategies to overcome resistance such as combination of mAbs on different pathways are briefly discussed as well.

Summary

The EGFR family receptors, is considered as an attractive target for mAb development to inhibit their consecutive activities in tumour growth and resistance. However, due to resistance mechanisms, the combination therapies may become a good candidate for targeting EGFR family receptors.

Paeoniflorin influences breast cancer cell proliferation and invasion via inhibition of the Notch‑1 signaling pathway

Breast cancer is one of the most frequently occurring malignant tumors affecting women's health. At least one million new cases are diagnosed each year. Therefore, research that aims to identify strategies that inhibit the growth of breast cancer cells has become a primary worldwide focus. Traditional Chinese medicine (TCM) is regarded as a valuable resource in China, and numerous monomer compositions extracted from TCMs have been demonstrated to exhibit antitumor effects. The present study aimed to determine the impact of paeoniflorin (PF) on breast cancer cell proliferation and invasion, and to explore the mechanisms underlying its effects. Different concentrations of PF were applied to MCF‑7 cells at various time points and the Cell Counting kit‑8 assay was used to determine cell proliferation, a transwell invasion assay was employed to determine cell invasion, reverse transcription‑polymerase chain reaction was used to determine notch homolog‑1 (NOTCH‑1) and Hes family basic helix‑loop helix transcription factor (HES)‑1 mRNA expression levels, and western blotting was used to determine NOTCH‑1 and HES‑1 protein expression levels. The results demonstrated that PF inhibited the proliferation of MCF‑7 cells in a dose‑ and time‑dependent manner. Following treatment with different concentrations of PF, the total number of cells present in the PF‑treated groups was significantly lower when compared with the untreated control group (P<0.05). With increasing doses of PF, the rate of cell invasion significantly decreased, indicating a dose‑dependent association. NOTCH‑1 and HES‑1 mRNA expression levels were reduced when compared with the untreated control group, which reached a statistical significance following treatment with 15 and 30 µM PF (P<0.05). NOTCH‑1 and HES‑1 protein levels demonstrated a similar trend to the mRNA levels, whereby an increase in the concentration of PF was associated with a decrease in NOTCH‑1 and HES‑1 protein expression levels. The results of the present study therefore suggest that PF may inhibit the proliferation and invasiveness of breast cancer cells via inhibition of the NOTCH‑1 signaling pathway.

Emerging treatments for HER2-positive early-stage breast cancer: focus on neratinib

Over the last decades, a better understanding of breast cancer heterogeneity provided tools for a biologically based personalization of anticancer treatments. In particular, the overexpression of the human epidermal growth factor receptor 2 (HER2) by tumor cells provided a specific target in these HER2-positive tumors. The development of the monoclonal antibody trastuzumab, and its approval in 1998 for the treatment of patients with metastatic disease, radically changed the natural history of this aggressive subtype of breast cancer. These findings provided strong support for the continuous research in targeting the HER2 pathway and implementing the development of new anti-HER2 targeted agents. Besides trastuzumab, a series of other anti-HER2 agents have been developed and are currently being explored for the treatment of breast cancer patients, including those diagnosed with early-stage disease. Among these agents, neratinib, an oral tyrosine kinase inhibitor that irreversibly inhibits HER1, HER2, and HER4 at the intracellular level, has shown promising results, including when administered to patients previously exposed to trastuzumab-based treatment. This article aims to review the available data on the role of the HER2 pathway in breast cancer and on the different targeted agents that have been studied or are currently under development for the treatment of patients with early-stage HER2-positive disease with a particular focus on neratinib.

Pathological Complete Response to Neoadjuvant Trastuzumab Is Dependent on HER2/CEP17 Ratio in HER2-Amplified Early Breast Cancer

Purpose: To evaluate whether pathologic complete response (pCR) to neoadjuvant trastuzumab is dependent on the level of HER2 amplification.Experimental Design: 114 HER2-overexpressing early breast cancer patients who had received neoadjuvant trastuzumab were included in this study. Absolute HER2 and chromosome 17 centromere (CEP17) were measured by in situ hybridization analysis, and associations were examined between HER2/CEP17 ratio and tumor pCR status (commonly defined by ypT0 ypN0, ypT0/is ypN0, and ypT0/is).Results: In trastuzumab-treated patients, ypT0 ypN0 was achieved in 69.0% of patients with high-level amplification (HER2/CEP17 ratio > 6), but only in 30.4% of tumors with low-level amplification (ratio ≤ 6; P = 0.001). When pCR was defined by ypT0/is ypN0 or ypTis, 75.9% and 82.8% of tumors with high-level amplification had a complete response, whereas only 39.1%, and 38.3% with low-level amplification achieved pCR (P = 0.002 and P < 0.001, respectively). Logistic regression revealed that tumors with high-level amplification had a significantly higher probability achieving ypT0 ypN0 (OR, 5.08; 95% confidence interval, 1.86-13.90; P = 0.002) than tumors with low-level amplification, whereas no other clinicopathologic parameters were predictive of pCR. The association between high-level HER2 amplification and pCR was almost exclusively confined to hormone receptor (HR)-positive tumors (ypT0 ypN0: 62.5% vs. 24.0%, P = 0.014; ypT0/is ypN0: 75.0% vs. 28.0%, P = 0.005; and ypT0/is: 87.5% vs. 28.0%, P < 0.001), and was largely absent in HR-negative tumors.Conclusions: An HER2/CEP17 ratio of >6 in the pretherapeutic tumor biopsy is associated with a significantly higher pCR rate, particularly in HER2/HR copositive tumors, and can be used as a biomarker to predict response before neoadjuvant trastuzumab is initiated. Clin Cancer Res; 23(14); 3676-83. ©2017 AACR.