Beyond trastuzumab: new treatment options for HER2-positive breast cancer

HER2-positive tumors comprise 15% to 20% of all breast cancers (BC) and are associated with worse clinical outcomes [Slamon et al., Science 1987;235:177-82]. Trastuzumab is a humanized monoclonal antibody designed to target the extracellular domain of the HER2 receptor, and is the foundation of care of women with early and advanced HER2-positive BC. However, a significant proportion of patients with this type of BC display either primary or secondary resistance to trastuzumab. Therefore, in an effort to overcome such resistance and further improve the outcome of patients with HER2-positive disease, several new anti-HER2 agents are currently being developed. These include small molecules that inhibit the HER2 tyrosine kinase activity (lapatinib, neratinib), monoclonal antibodies directed at other epitopes of the HER2 extracellular domain (pertuzumab), antibody-drug conjugates (trastuzumab-DMl), and heat shock protein 90 inhibitors (tanespimycin). A great deal of interest has been generated by recent data from the randomized neo-adjuvant studies NeoALTTO and NeoSphere, which have shown that dual blockade of the HER2 receptor with anti-HER2 agents is significantly superior to using one agent alone. If these results are validated in larger ongoing and planned phase III studies in early BC, they could lead to a paradigm shift in treatment strategy. Therefore, to avoid unnecessary toxicities and costs, it is critical to intensify the research for biomarkers that can identify those patients most likely to benefit from specific targeted therapies.     

Cost-effectiveness of trastuzumab biosimilar combination therapy and drug wastage as first-line treatment for HER2-positive metastatic breast cancer

BackgroundThe rising cost of cancer drug therapy threatens the long-term sustainability of Taiwan National Health Insurance. Cost savings can be achieved through various strategies, e.g., using smaller vial sizes, sharing vials, weight-based dosing, or switching to biosimilars. Here we aimed to examine the cost-effectiveness of a trastuzumab biosimilar combined with docetaxel (TDbiol) for treatment-naïve HER2⁺ metastatic breast cancer (MBC), and the financial impact of drug wastage.MethodsA Markov model with three health states was developed to assess the cost-effectiveness of trastuzumab biosimilars plus docetaxel over a 40-month time horizon in patients with HER2⁺ MBC. Based on the literature and our expert opinion, we assumed similar efficacy between the trastuzumab biosimilar and its reference product. The primary clinical input for the biosimilar was the same as for the reference product in the Catastrophic Patient Database (HV). Health state utilities were derived from the literature, and direct medical costs were obtained from the National Health Insurance Administration (NHIA).ResultsIn the base-case scenario, the incremental cost-effectiveness ratio (ICER) was NTD 811,050 per QALY gained. One-way sensitivity analyses showed that the model was sensitive to utilities and transition probabilities, but not particularly sensitive to the wastage assumption. In scenario analyses, the ICER was higher when applying the price for trastuzumab reference biologic (branded), than for trastuzumab biosimilar.ConclusionThe trastuzumab biosimilar combination regimen is cost-effective and offers significant drug cost savings in Taiwan.     

Treatment of HER2-positive breast cancer

The human epidermal growth factor receptor 2 gene (HER2) is overexpressed and/or amplified in ∼15% of breast cancer patients and was identified a quarter century ago as a marker of poor prognosis. By 1998, antibody therapy targeting the HER2 pathway was shown to demonstrably improve progression-free and overall survival in metastatic disease, and in 2005 evidence of improvement in disease-free and overall survival from the first generation of trastuzumab adjuvant trials became available. However, not all patients with HER2 overexpression benefit from trastuzumab. Second-generation studies in metastatic disease led to the approval of several new HER2-targeted therapies using small molecule tyrosine kinase inhibitors such as lapatinib, new HER2/HER3 antibodies such as pertuzumab, and the new antibody chemotherapy conjugate ado-trastuzumab emtansine. These successes supported the launch of second-generation adjuvant trials testing single and dual HER2-targeted agents, administered concomitantly or sequentially with chemotherapy that will soon complete accrual. HER2-positive breast cancer in the setting of HER2-targeted therapy is no longer associated with poor prognosis, and recent guidance by the US Food and Drug Administration suggests that pathologic response to HER2-targeted therapy given preoperatively may allow an earlier assessment of their clinical benefit in the adjuvant setting. An adjuvant trial of trastuzumab in patient whose tumors express normal levels of HER2 and trials of single/dual HER2-targeting without chemotherapy are also ongoing. In this article, we review the current data on the therapeutic management of HER2-positive breast cancer.     

First report of eribulin in combination with pertuzumab and trastuzumab for advanced HER2-positive breast cancer

BackgroundThe efficacy and safety of continuing multiple anti-HER2 therapies in advanced breast cancer (ABC) patients remains unclear. This study investigated eribulin in combination with pertuzumab and trastuzumab for both taxane- and trastuzumab-pretreated HER2-positive ABC patients.MethodsIn a single-institute, single-arm, open-label, phase II trial, HER2-positive ABC patients who had previously received taxanes and trastuzumab were treated with eribulin in combination with pertuzumab and trastuzumab. The pharmacokinetics of eribulin in this combination were assessed in 6 patients. Tumor assessments were conducted every 6 weeks for the first 6 cycles and every 12 weeks thereafter. The primary endpoint was objective response rate (ORR).ResultsA total of 30 patients (median age, 58 years; range, 31–76) were enrolled, with a median number of previous chemotherapy regimens of 3.5 (range: 1–9) in the metastatic setting. Pharmacokinetic parameters of eribulin in this combination were similar to previous reports of eribulin monotherapy. ORR was 34.8% (95% CI: 16.4–57.3, n = 23), and median progression-free survival was 42.6 weeks (95% CI: 20.3–51.9, n = 30). Clinical benefit rate was 60.9% (95% CI: 16.4–57.3). The most common grade 3/4 adverse event was neutropenia in 20 patients (66.7%). A dose reduction of eribulin was required in 27 patients due to adverse events, particularly grade 3 neutropenia.ConclusionsEribulin in combination with pertuzumab and trastuzumab was well tolerated in heavily pretreated patients. Eribulin may be a viable treatment option when used in combination with pertuzumab and trastuzumab for HER2-positive ABC patients (UMIN Clinical Trial Registry identification number, UMIN000012375).     

T-DM1 and brain metastases: Clinical outcome in HER2-positive metastatic breast cancer

BackgroundWe reported the results of an Italian large retrospective analysis that evaluated the effectiveness and safety of T-DM1 in ‘field-practice’ breast cancer patients. We performed a sub-analysis to investigate the clinical activity of T-DM1 in patients with brain metastases (BMs).MethodsThe records of 87 adult women with HER2-positive breast cancer and BMs treated with T-DM1 were reviewed. Their clinical outcomes were compared with those of 216 patients without central nervous system (CNS) involvement.ResultsResponse to T-DM1 treatment in BMs was available for 53 patients in the BM group (60.9%): two patients reported a complete response (3.8%), 11 patients obtained partial response (20.7%; overall response rate: 24.5%), 16 patients had a stable disease (30.1%). Regarding extracranial disease, a total of 77 and 191 patients were evaluable for response in BM group and non-BM group, respectively. The overall response rate was 35.1% in the BM group and 38.3% in the non-BM group; disease control rate was 53.3% and 66.6%, respectively.At a median follow-up of 16 months (range: 1–55), median cumulative progression-free survival (PFS) was 7 months (95% CI: 5.4–8.6) in the BM group and 8 months (95% CI: 5.7–10.3) in the non-BM group. In the second-line setting, PFS was 5 (95% CI: 3.1–6.9) versus 11 (95% CI: 7.1–14.9) months (p = 0.01). Overall survival was 14 months (95% CI: 12.2–15.8) in the BM group and 32 months (95% CI: 24.4–39.6) in the non-BM group (p < 0.0001).ConclusionsT-DM1 is active in breast cancer patients with BMs.     

Characteristics of patients with brain metastases receiving trastuzumab for HER2 overexpressing metastatic breast cancer

The intention of this retrospective analysis was to describe the characteristics of patients with brain metastasis (BM) receiving trastuzumab for HER2 overexpressing metastatic breast cancer (MBC). A specific focus was the relation of BM occurrence to remission status of visceral disease during trastuzumab treatment. Patients with MBC presenting between March 2000 and May 2004 were included in this retrospective analysis. HER2 overexpression was determined by immunohistochemistry (IHC; DAKO Hercep Test). Trastuzumab was applied at a loading dose of 4 mg/kg and a maintenance dose of 2 mg/kg. Among 136 HER2 overexpressing patients (DAKO score 3+), 42 patients with BM were identified during follow-up (30.9%). Negative hormone receptor expression (estrogen receptor (ER) and progesterone receptor (PgR)) correlated with incidence of BM (42.8% vs. 23.4%; P=0.01). There was no correlation of the development of BM with regard to tumor grading and patient age. In patients who developed BM, the median interval between visceral and brain metastasis was 14 months (range 0-69 months). At the time BM was diagnosed, 14 out of 42 patients responded to trastuzumab-based treatment schedules (OR: 33.3%, 95% CI 18.5-48.2%). Median survival from diagnosis of BM was 13 months (range 0-60 months). The median overall survival calculated from first diagnosis of metastasis was not significantly shorter in patients with BM than in patients without BM (37 vs. 47 months; P=0.07 log rank). Trastuzumab is highly effective for the treatment of liver and lung metastasis in HER2 overexpressing patients, while it is apparently ineffective for treating or preventing BM. Since one third of HER2 overexpressing patients with MBC developed BM despite effective trastuzumab treatment, new treatment strategies and closer surveillance may be warranted for these patients.     

Histopathologic characteristics predicting HER-2/neu amplification in breast cancer

The HER-2/neu gene is a proto-oncogene that is amplified in 10-30% of breast cancers. New drugs for targeted therapy, such as Herceptin, are effective for patients with HER-2/neu-positive tumors, making it necessary to have a noncostly and accurate method to assess HER-2/neu status. We studied the correlation of findings made by fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC) staining and the possibility of combining IHC and other clinicopathologic characteristics of breast tumors to predict FISH-determined HER-2/neu status. The clinicopathologic characteristics analyzed were the size of the tumor, p53, lymph-vascular invasion, estrogen/progesterone receptors (ER/PR), tumor grade, axillary lymph node status, and patient age. A total of 199 cases of invasive breast cancer studied at the UCLA Pathology Laboratory during 2003 were included in this study. Tumors with IHC 0, 1+, 2+, and 3+ scores were found to be FISH positive in 3.5%, 6.4%, 25.7%, and 81.5% of the respective groups. Our study showed a strong association between the FISH-negative and IHC scored 0 and 1+ tumors, suggesting that the FISH test may not be necessary in these cases (p<0.0001). Although the concordance between IHC 3+ and FISH positive is high, 18% of the patients with overexpression of HER-2/neu fail to show gene amplification by FISH. HER-2/neu positivity was found to be proportionally associated with increasing grade in infiltrating ductal carcinoma (p<0.0001). p53-positive tumors are more likely to be HER-2/neu amplified (p=0.0003). Tumors that are negative for ER/PR are also associated with HER-2/neu positivity by FISH (31.15%, p=0.0016). FISH-determined HER-2/neu status is not associated with histologic type, tumor size, nodal status, lymph-vascular invasion, or patient age.     

Impacts of clinicopathological factors on efficacy of trastuzumab deruxtecan in patients with HER2-positive metastatic breast cancer

BackgroundThe previous second-line treatment for HER2-positive metastatic breast cancer were ado-trastuzumab emtansine (T-DM1); however, its activity is decreased in tumors with heterogenous, reduced, or loss of HER2 expression. Trastuzumab deruxtecan (T-DXd) has recently been developed as a novel antibody-drug conjugate to overcome resistance to T-DM1. However, clinical evidence on its ability to overcome this resistance is limited.Materials and methodsWe retrospectively analyzed data for patients with HER2-positive metastatic breast cancer who received T-DXd at our institution from April 2020 to March 2021. We evaluated the associations between clinicopathological and molecular biomarkers and the efficacy of T-DXd.ResultsTwenty-two patients were enrolled in this study. The median progression-free survival (PFS) was 9.7 months (95% confidence interval [CI], 7.0–not reached [NR]), and the objective response rate (ORR) was 61.9%. The ORR and PFS were comparable between patients with HER2 immunohistochemistry scores of 3+ and 2+/1+ at initial diagnosis (ORR: 50.0% vs. 72.7%, p = 0.39; median PFS, 9.7 months [95%CI, 2.6–NR] vs. 8.3 months [95%CI, 7.1–NR]; hazard ratio, 1.86 [95%CI, 0.53–6.57], p = 0.34). Two patients with heterogenous HER2 expression had a partial response or long stable disease (≥6 months). Three of four patients with re-biopsy samples after anti-HER2 targeted therapy and with latest HER2 immunohistochemistry scores of 1+ experienced partial responses (75.0%) to T-DXd, but none had responded to prior T-DM1.ConclusionsT-DXd demonstrated favorable activity in clinical practice. Moreover, T-DXd showed meaningful benefit in patients with heterogeneity, reduction, or loss of HER2 expression.     

The role of c-erbB-2/HER2/neu in breast cancer progression and metastasis

Gene amplification and/or overexpression of the c-erbB-2/HER2/neu tyrosine kinase are linked with poor prognosis in breast cancer. This is manifest in shorter disease-free intervals, increased risk of metastasis, and resistance to many types of therapy. The molecular mechanisms and signaling circuitry underlying these phenomena are now being elucidated. c-erbB-2, although having no known soluble ligand, is transactivated by heterodimerization with other family members (EGFR, c-erbB-3, c-erbB-4). Receptor activation potentiates tumor cell motility, protease secretion and invasion, and also modulates cell cycle checkpoint function, DNA repair, and apoptotic responses. Since it is expressed at low levels in normal adult tissues, c-erbB-2 is an ideal target for therapy. There is reason for optimism that agents targeting c-erbB-2 signaling will have profound and selective effects in breast cancer, either as single agents or more likely in combination with other therapeutic agents, to enhance their potency.     

The association of HER-2/neu amplification with breast cancer recurrence

HYPOTHESIS: Amplification of the HER-2/neu oncogene in 25% of breast cancers is associated with a shortened disease-free survival. DESIGN: Retrospective analysis of a patient population referred to a tertiary care facility for HER-2/neu testing. The mean follow-up was 56 months. SETTING: Large, urban, tertiary care hospital. PATIENTS: From 1995 to 1999, a consecutive sample of 190 patients with breast cancer had tissue samples tested for overexpression of the cell surface oncoprotein by immunostaining (IM) or amplification of the HER-2/neu oncogene by fluorescence in situ hybridization or both. Forty-nine subjects were excluded because they had tissue samples tested at our institution but received their treatment elsewhere. All patients tested for HER-2/neu after diagnosis with breast cancer in 1999 (n = 47) were excluded from analysis because of short follow-up time. One patient was excluded who had in situ ductal carcinoma. The remaining 93 patients were analyzed. RESULTS: Of 93 patients, 40 (43%) had gene amplification. Overall, patients with oncogene amplification had a shorter median disease-free interval (22 months) compared with controls (40 months) (P =.003). Analysis by the Cox regression model showed that the HER-2/neu status remained significantly associated with time to relapse even after adjusting for age and tumor grade (P =.002; adjusted relative risk, 2.4; 95% confidence interval, 1.4-4.4). No association was found between gene amplification and tumor grade (P =.98), estrogen/progesterone receptor status (P = .29 and P = .43, respectively), or lymph node status (P = .98). Seventy-two patients (77%) eventually had disease recurrence, with 18 (25%) of these recurring locally. CONCLUSIONS: The HER-2/neu oncogene is an independent prognostic indicator of a subset of breast cancers that are at high risk of early recurrence, regardless of tumor grade, estrogen/progesterone receptor status, and lymph node status. Patients amplifying the HER-2/neu oncogene have a shorter disease-free survival than patients without the oncogene.     

Role of endocrine responsiveness and HER2/neu overexpression in inflammatory breast cancer treated with multimodality preoperative therapy

We analyzed the role of endocrine responsiveness and HER2/neu overexpression in inflammatory breast cancer treated with multimodality preoperative therapy. Thirty-eight patients (estrogen receptor [ER] and/or progesterone receptor [PgR] >or=10% of the cells 21, premenopausal 14, Ki-67 expression >or=20% of the cells 30, HER2/neu overexpressed 11) were treated with six courses of epirubicin, cisplatin and fluorouracil (FU) as continuous infusion, perioperative FU as continuous infusion, mastectomy and loco-regional radiotherapy. In endocrine-responsive patients, endocrine treatment (letrozole, either alone or if premenopausal with triptorelin) was given preoperatively and as adjuvant treatment. There were 32 objective responders (84.2%; 95% CI 70.0-94.6%), three of whom had pathologic complete remission. At the multivariate analysis disease-free survival was significantly worse in patients with ER and PgR absent tumors compared with the positive expression cohort (hazards ratio [HR]: 5.91; 95% CI 1.69-20.7; p = 0.005), in particular if HER2/neu overexpression was detected (HR: 16.5; 95% CI 4.24-64.5; p < 0.0001). New multimodality and targeted strategies should be explored in endocrine nonresponsive breast cancer.     

Dissecting the biological heterogeneity of HER2-positive breast cancer

HER2-positive (HER2+) breast cancer (BC) is a heterogenous and multifaceted disease, with interesting therapeutic implications. First, all intrinsic molecular subtypes can be identified in HER2+ tumors, with the HER2-enriched being the most frequent. Such subtypes do not differ much from their counterparts in HER2-negative disease, apart for the high expression of genes in/near the HER2 amplicon on chromosome 17. Intrinsic subtyping, along with the quantification of ERBB2 mRNA levels, is associated with higher rates of pathologic complete response across neoadjuvant trials of dual HER2 blockade and might help select patients for de-escalation and escalation treatment strategies. Secondly, HER2+ tumors have a broad range of DNA alterations. ERBB2 mutations and alterations in the PI3K/Akt/mTOR pathway are among the most frequent and might predict benefit from potent pan-HER, PI3K and mTOR inhibitors. Moreover, HER2+ tumors are usually infiltrated by lymphocytes. These tumor infiltrating-lymphocytes (TILs) predict response to neoadjuvant anti-HER2-based treatment and exert a prognostic role. PD-L1, detected in ∼42 % of HER2+ BC, might also be useful to define patients responding to novel anti-PD1/PD-L1 immunotherapies. New multiparametric clinicopathologic and genomic tools accounting for this complexity, such as HER2DX, are under development to define more tailored treatment approaches. Finally, HER2-targeted antibody-drug conjugates (ADC) such as trastuzumab deruxtecan might be active in tumors with low expression of HER2. Overall, there is a need to molecularly characterize and develop novel targeted therapies for HER2+ disease.     

Peripheral cytotoxic T lymphocyte predicts first-line progression free survival in HER2-positive advanced breast cancer

BackgroundThe role of peripheral blood lymphocyte (pBL) in breast cancer has long been studied. However, the predictive role of pBL in advanced breast cancer (ABC) is poorly understood.MethodsA total of 303 patients with ABC were consecutively recruited at our center between January 2015 and September 2019. At baseline, pBL subtypes were detected in all patients with 229 blood samples available for circulating tumor DNA (ctDNA) detection. pBL was analyzed through flow cytometry. ctDNA-based gene mutations were detected using next generation sequencing. The cutoff value of pCTL was estimated by X-tile software. Progression free survival (PFS) was estimated by Kaplan-Meier curve and Cox hazard proportion regression model, with difference detection by log-rank test.ResultsMedian follow-up time of the study was 21.0 months. The median age of diagnosis was 52.0 years. Among the pBL subtypes, only pCTL level was found predictive for PFS in the HER2+ patients whom received anti-HER2 therapy (13.1 vs. 5.6 months, P = 0.001). However, the predictive role of pCTL was not found in HR-positive (P = 0.716) and TNBC (P = 0.202). pCTL high associated with suppressive immune indictors including lower CD4/CD8 ratio (P = 0.004) and high level of Treg cell (P = 0.004). High occurrence of FGFR1 amplification which has been reported as immune suppressor was also found in HER2+ patients with pCTL high (22.2% vs. 4.3%, P = 0.048).ConclusionsHigher pCTLs level associated with shorter PFS and FGFR1 mutation in HER2+ ABC patients.     

Current and emerging therapies of HER2-positive metastatic breast cancer

The HER2 receptor as measured by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) is overexpressed in 15–20% of all breast cancers and traditionally represents adverse biology and a guarded prognosis, particularly in HER2 positive metastatic breast cancer (MBC). Trastuzumab and newer anti-HER2 targeting agents have significantly improved the clinical outcomes of patients with HER2 positive MBC. The development of new techniques has led to discovery of promising biomarkers that can lead to more precise selection of patients for anti-HER2 therapies. This paper summarizes these new biomarkers, useful in selecting patients for treatment with new and emerging therapies for HER2 positive MBC. Emerging next generation sequencing techniques have truly changed the landscape of HER2 positive MBC. Deployment of multiple anti-HER2 therapies in combination is a strategy which has yielded additive or even synergistic effects and has led to markedly improved patient outcomes in HER2+ MBC. In the future, in order to further improve the treatment of these patients and to reduce toxicities, we need to improve our understanding of HER2-dependent pathways and their function, and to develop further treatment combinations while optimizing selection of patients by identifying new biomarkers. The results of prospective studies using CTCs, cDNA and other promising new biomarkers are awaited with great interest.     

HER2/neu表达对乳腺癌术后应用CMF化疗病人预后的影响

目的：研究HER2/neu癌基因在乳腺癌组织中的表达，探讨其对接受手术及CMF（环磷酰胺、氨甲碟呤和氟脲嘧啶）辅助化疗病人预后的影响。方法：选择1995年至2001年间112例接受手术和术后行CMF化疗的乳腺癌病人的组织标本，用免疫组织化学方法检测原发肿瘤HER2/neu蛋白及雌孕激素受体的表达，结合临床病理资料并分析其与5年生存率的关系。结果：本组乳腺癌组织中HER2/neu的过度表达率为21．4％（n=24）。经随访13～104月，整体病人的5年无病生存率为85．3％，5年总体生存率为91．1％。HER2／neu过度表达者的5年无病生存率为43．2％，而HER2/neu表达缺失者为71％（P=0．01）。HER2/neu过度表达者的5年总体生存率为49．2％，而HER2/neu表达缺失者为83.3％（P=0．02）。同时，生存率亦与肿瘤大小和孕激素受体密切相关。结论：乳腺癌组织中HER2/neu蛋白的过度表达与接受手术及术后CMF化疗病人的预后密切相关，可以作为预测其复发及转移的重要指标。     

HER2-positive breast cancer: Current and new therapeutic strategies

Since the identification of the HER2 receptor amplification as an adverse prognostic factor that defined a special subtype of metastatic breast cancer, there has been a substantial improvement in survival of patients affected with this disease due to the development of anti-HER2 targeted therapies. The approval of trastuzumab and pertuzumab associated to a taxane in first line and subsequent treatment with the antibody-drug conjugate T-DM1 has certainly contributed to achieve these outcomes. The Tyrosine Kinase Inhibitor lapatinib was also approved in the basis of an improvement in progression free survival, becoming another commonly used treatment in combination with capecitabine. Inevitably, despite these therapeutic advances most patients progress on therapy due to primary or acquired resistance or because of an incorrect HER2 positivity assessment. Hence, it is crucial to correctly categorize HER2 amplified tumors and define mechanisms of resistance to design effective new treatment approaches. In addition, identifying biomarkers of response or resistance permits to tailor the therapeutic options for each patient sparing them from unnecessary toxicity as well as improving their outcomes. The aim of this review is to examine new strategies in development to treat HER2-positive metastatic breast cancer referring to the mechanisms of action of new drugs and new combinations including results reported so far.     

Response of bilateral choroidal metastases of breast cancer to therapy with trastuzumab

Intraocular metastases, especially those of the choroidal plexus, are not common in metastatic breast cancer patients and are typically associated with a poor prognosis and impaired quality of life. A 45-year-old woman with breast cancer overexpressing HER2 and metastasizing to choroidal plexus, lymph nodes and skin received a combination of trastuzumab and paclitaxel as first-line treatment. Subsequently, at progression, trastuzumab was reintroduced together with vinorelbine. Administration of trastuzumab with either paclitaxel or vinorelbine led to a rapid improvement of the ocular symptoms, associated with a rapid objective response of all metastatic lesions and a prompt improvement in the quality of life. Choroidal metastases from breast cancer overexpressing HER2 are responsive to trastuzumab and chemotherapy (paclitaxel or vinorelbine). The susceptibility of ocular metastases to this approach seems different to that of other sanctuary disease sites.     

Efficacy of CT-P6 (trastuzumab biosimilar) versus reference trastuzumab in combination with pertuzumab in HER2-positive early-stage breast cancer: Preclinical and real-life clinical data

After the expiration of trastuzumab data exclusivity, biosimilar drugs were approved by regulatory agencies; among them, CT-P6 which was approved for the treatment of HER2-positive early- and advanced-breast cancer (BC) in 2018. Yet, reference trastuzumab (RTZ) is often combined with pertuzumab in early BC (EBC) patients treated with chemotherapy as it significantly improves the pathological complete response rate. Unfortunately, scarce preclinical and clinical data exists about the combination of CT-P6, pertuzumab and chemotherapy. Therefore, our aim was to study in vitro and in a retrospective cohort of EBC patients, whether CT-P6 was equivalent to RTZ when combined with pertuzumab with or without taxanes. In BT-474 and SKBR3 HER2+ cells we found that CT-P6 alone or in combination with pertuzumab had the same negative effect on cell proliferation, colony formation and HER2 downregulation as well as downstream activation, as RTZ. Adding paclitaxel to these treatments increased their effectivity to a similar extent. In HER2 1+ neuregulin-secreting MB-MDA-175 cells, combinations of CT-P6 or RTZ with pertuzumab were also effective, and mainly dependent on HER3:HER2 heterodimerization. In a retrospective cohort of 44 EBC HER2+ patients treated with neoadjuvant RTZ or CT-P6 in combination with pertuzumab and chemotherapy, we found no differences in efficacy or in adverse events. Moreover, the costs of CT-P6-based treatments were reduced by 1474.07 €/patient. All together we provide pre-clinical and clinical evidence of the equivalence of CT-P6 in combination with pertuzumab and chemotherapy and suggest studying these combinations also in HER2 low/negative BC patients.