Dual Characteristics of Novel HER2 Kinase Domain Mutations in Response to HER2-Targeted Therapies in Human Breast Cancer

The molecular subtyping and precision medicine in triple-negative breast cancer---based on Fudan TNBC classification

Triple-negative breast cancer (TNBC) is widely recognized as the most aggressive form of breast cancer, occurring more frequently in younger patients and characterized by high heterogeneity, early distant metastases and poor prognosis. Multiple treatment options have failed to achieve the expected therapeutic effects due to the lack of clear molecular targets. Based on genomics, transcriptomics and metabolomics, the multi-omics analysis further clarifies TNBC subtyping, which provides a greater understanding of tumour heterogeneity and targeted therapy sensitivity. For instance, the luminal androgen receptor subtype (LAR) exhibits responsiveness to anti-AR therapy, and the basal-like immune-suppressed subtype (BLIS) tends to benefit from poly (ADP-ribose) polymerase inhibitors (PARPis) and anti-angiogenic therapy. The efficacy of multi-dimensional combination therapy holds immense importance in guiding personalized and precision medicine for TNBC. This review offers a systematic overview of recent FuDan TNBC molecular subtyping and its role in the instruction of clinical precision therapy.

Emerging Landscape of Targeted Therapy of Breast Cancers With Low Human Epidermal Growth Factor Receptor 2 Protein Expression

CONTEXT.—

Human epidermal growth factor receptor 2 (HER2) status in breast cancer is currently classified as negative or positive for selecting patients for anti-HER2 targeted therapy. The evolution of the HER2 status has included a new HER2-low category defined as an HER2 immunohistochemistry score of 1+ or 2+ without gene amplification. This new category opens the door to a targetable HER2-low breast cancer population for which new treatments may be effective.

OBJECTIVE.—

To review the current literature on the emerging category of breast cancers with low HER2 protein expression, including the clinical, histopathologic, and molecular features, and outline the clinical trials and best practice recommendations for identifying HER2-low-expressing breast cancers by immunohistochemistry.

DATA SOURCES.—

We conducted a literature review based on peer-reviewed original articles, review articles, regulatory communications, ongoing and past clinical trials identified through ClinicalTrials.gov, and the authors' practice experience.

CONCLUSIONS.—

The availability of new targeted therapy potentially effective for patients with breast cancers with low HER2 protein expression requires multidisciplinary recognition. In particular, pathologists need to recognize and identify this category to allow the optimal selection of patients for targeted therapy.

Targeting HER2-mutant metastatic cervical cancer with neratinib: Final results from the phase 2 SUMMIT basket trial

OBJECTIVE

HER2 mutations are associated with poor prognosis and are detected in 3-6% of cervical cancers. Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, had activity in several HER2-mutant cancer types in the phase 2 SUMMIT basket study. We present updated and final results from the cervical cancer cohort of SUMMIT.

METHODS

Eligible patients had HER2-mutant, metastatic or recurrent cervical cancer progressing after platinum-based treatment for advanced/recurrent disease. Patients received neratinib 240 mg/day; loperamide was mandatory during cycle 1. Confirmed objective response rate (ORR) was the primary endpoint. Duration of response (DoR), clinical benefit rate (CBR), progression-free survival (PFS), and safety were secondary endpoints.

RESULTS

Twenty-two patients were enrolled; 18 (81.8%) had endocervical adenocarcinoma; median two prior systemic chemotherapy regimens (range 1-4). The most common HER2 variant was S310F/Y mutation (n = 13; 59.1%). Four patients had confirmed partial responses (ORR 18.2%; 95% CI 5.2-40.3); 6 had stable disease ≥16 weeks (CBR 45.5%; 95% CI 24.4-67.8). Median DoR was 7.6 months (95% CI 5.6-12.3). Median PFS was 5.1 months (95% CI 1.7-7.2). All-grade diarrhea (90.9%), nausea (54.5%), and constipation (54.5%) were the most common adverse events. Five patients (22.7%) reported grade 3 diarrhea. There were no grade 4 adverse events, no diarrhea-related treatment discontinuations, and two grade 5 adverse events, unrelated to neratinib: dyspnea (n = 1) and embolism (n = 1).

CONCLUSIONS

Neratinib resulted in durable responses and disease control in patients with HER2-mutant metastatic/recurrent cervical cancer in SUMMIT. These findings support next-generation sequencing and tailored therapy for select patients with advanced cervical cancer. All responses occurred in patients with endocervical adenocarcinoma. Further assessment of neratinib in this setting is warranted.

TRIAL REGISTRATION NUMBER

NCT01953926 (ClinicalTrials.gov), 2013-002872-42 (EudraCT).

PRESSING Need of Precision Care in HER2-Positive Colorectal Cancer: The ELEPHANT in the Room

Although dual HER2 inhibition has shown promising clinical activity in patients with RAS wild-type HER2-positive metastatic colorectal cancer, predictive biomarkers of response/resistance are less well characterized. Activating HER2/RTK/MAPK genomic alterations appears to blunt the clinical benefit of dual anti-HER2 therapy and may hold a potential albeit partial role in patient selection. See related article by Randon et al., p. 436.

Development of a cancer metastasis-on-chip assay for high throughput drug screening

Metastasis is the cause of most triple-negative breast cancer deaths, yet anti-metastatic therapeutics remain limited. To develop new therapeutics to prevent metastasis, pathophysiologically relevant assays that recapitulate tumor microenvironment is essential for disease modeling and drug discovery. Here, we have developed a microfluidic metastasis-on-chip assay of the early stages of cancer metastasis integrated with the triple-negative breast cancer cell line (MDA-MB-231), stromal fibroblasts and a perfused microvessel. High-content imaging with automated quantification methods was optimized to assess the tumor cell invasion and intravasation within the model. Cell invasion and intravasation were enhanced when fibroblasts co-cultured with a breast cancer cell line (MDA-MB-231). However, the non-invasive breast cancer cell line, MCF7, remained non-invasive in our model, even in the presence of fibroblasts. High-content screening of a targeted anti-cancer therapy drug library was conducted to evaluate the drug response sensitivity of the optimized model. Through this screening, we identified 30 compounds that reduced the tumor intravasation by 60% compared to controls. Multi-parametric phenotypic analysis was applied by combining the data from the metastasis-on-chip, cell proliferation and 2D cell migration screens, revealing that the drug library was clustered into eight distinct groups with similar drug responses. Notably, MEK inhibitors were enriched in cluster cell invasion and intravasation. In contrast, drugs with molecular targets: ABL, KIT, PDGF, SRC, and VEGFR were enriched in the drug clusters showing a strong effect on tumor cell intravasation with less impact on cell invasion or cell proliferation, of which, Imatinib, a multi-kinase inhibitor targeting BCR-ABL/PDGFR/KIT. Further experimental analysis showed that Imatinib enhanced endothelial barrier stability as measured by trans-endothelial electrical resistance and significantly reduced the trans-endothelial invasion activity of tumor cells. Our findings demonstrate the potential of our metastasis-on-chip assay as a powerful tool for studying cancer metastasis biology, drug discovery aims, and assessing drug responses, offering prospects for personalized anti-metastatic therapies for triple-negative breast cancer patients.

Clinical characteristics and treatment outcomes of HER2 mutation and HER2 fusion in 22 patients with advanced breast cancer

BACKGROUND

The clinical characteristics and efficacy of human epidermal growth factor receptor-2 (HER-2)-directed agents against HER2 mutations and HER2 fusions in breast cancer are obscure due to their low frequency.

METHODS

We conducted a retrospective study in patients with advanced breast cancer harboring HER2 mutations and/or HER2 fusions between January 1, 2017 and January 1, 2021.

RESULTS

Among a total of 22 patients, 17 HER2 mutations were detected, including L755S, S310F, R100=, V777L, R897W, T862A, 440-17C > G, H878Y, V842I, 73 + 9G > C, T278fs, E1069K, L755P, 226-11C > T, 574 + 12C>T, L114V and P128L. The majority of patients had ductal carcinoma, which mostly coexisted with HER2 amplification/overexpression. The median progression-free survival (PFS) of the 22 patients was 6.9 months (95% CI: 4.7, 9.1) in the first-line setting. The median PFS of patients who received first-line trastuzumab-based regimens was significantly longer than that of patients who received a first-line tyrosine kinase inhibitor (TKI) (10.8 months [95% CI: 2.9, 18.7] vs. 1.9 months [95% CI: 0.8, 3.0], p < 0.005). A total of 14 patients were treated with anti-HER2 antibody-drug conjugate (ADC), among whom the median treatment line of first-time of administration of anti-HER2 ADC was 4.5 (range, 1-10). Anti-HER2 ADC reached an objective response rate (ORR) of 42.9%, a disease control rate (DCR) of 85.7% and a median PFS of 7.3 months (95% CI: 4.4-10.1) from the first-time of administration.

CONCLUSION

Our data demonstrated the clinical benefit of anti-HER2 treatment in Chinese breast cancer patients harboring HER2 mutation and/or HER2 fusion. The value of immunotherapy and treatment selection among individual HER2 variants needs further study.

Efficacy of anti-HER2 drugs in the treatment of patients with HER2-mutated cancers: a systematic review and meta-analysis

Anti-human epidermal growth factor receptor-2 (anti-HER2) therapy has shown excellent efficacy in patients with HER2 overexpression and amplification. Although HER2 mutations are rarely expressed in several cancers, when they occur, they can activate the HER2 signaling pathway. In recent years, studies have shown that anti-HER2 drugs have promising efficacy in patients with HER2 mutations. Based on keywords, we searched databases, such as PubMed, Embase, and Cochrane Library, and the main conference abstracts. We extracted data on objective response rate (ORR), clinical benefit rate (CBR), duration of response (DOR), progression-free survival (PFS), and overall survival (OS) from studies on the efficacy of anti-HER2 therapies in patients with HER2-mutated cancers, and analyzed grade 3 or higher adverse events (AEs). We included 19 single-arm clinical studies and 3 randomized controlled trials (RCTs), containing a total of 1017 patients with HER2 mutations, involving seven drugs and nine cancers, and 18 studies enrolled a high proportion of heavily pretreated patients who had received multiple lines of therapy. Our results showed pooled ORR and CBR of 25.0% (range, 3.8-72.7%; 95% CI, 18-32%) and 36.0% (range, 8.3-63.0%; 95% CI, 31-42%) for anti-HER2 therapy in HER2-mutated cancers. The pooled median PFS, OS, DOR were 4.89 (95% CI, 4.16-5.62), 12.78 (95% CI, 10.24-15.32), and 8.12 (95% CI, 6.48-9.75) months, respectively. In a subgroup analysis, we analyzed the ORR for different cancers, showing 27.0, 25.0, 23.0, and 16.0% for breast, lung, cervical, and biliary tract cancers, respectively. ORR analyses were performed for different drugs as monotherapy or in combination, showing 60.0% for trastuzumab deruxtecan (T-DXd), 31.0% for pyrotinib, 26.0% for neratinib combined with trastuzumab, 25.0% for neratinib combined with fulvestrant, 19.0% for trastuzumab combined with pertuzumab, and 16.0% for neratinib. In addition, we found that diarrhoea, neutropenia, and thrombocytopenia were the most common grade ≥ 3 AEs associated with anti-HER2 therapeutic agents. In this meta-analysis of heavily pretreated patients with HER2 mutations, anti-HER2 therapies, DS-8201 and trastuzumab emtansine, showed promising efficacy and activity. Anti-HER2 therapies showed different efficacies in different or the same cancer settings and all had a tolerable safety profile.

Systemic Therapy for Metastatic Triple Negative Breast Cancer: Current Treatments and Future Directions

Until recently, despite its heterogenous biology, metastatic triple negative breast cancer (TNBC) was treated as a single entity, with successive lines of palliative chemotherapy being the only systemic option. Significant gene expression studies have demonstrated the diversity of TNBC, but effective differential targeting of the four main (Basal-like 1 and 2, mesenchymal and luminal androgen receptor) molecular sub-types has largely eluded researchers. The introduction of immunotherapy, currently useful only for patients with PD-L1 positive cancers, led to the stratification of first-line therapy using this immunohistochemical biomarker. Germline BRCA gene mutations can also be targeted with PARP inhibitors in both the adjuvant and metastatic settings. In contrast, the benefit of the anti-Trop-2 antibody-drug conjugate (ADC) Sacituzumab govitecan (SG) does not appear confined to patients with tumours expressing high levels of Trop-2, leading to its potential utility for any patient with an estrogen receptor (ER)-negative, HER2-negative advanced breast cancer (ABC). Most recently, low levels of HER2 expression, detected in up to 60% of TNBC, predicts benefit from the potent HER2-directed antibody-drug conjugate trastuzumab deruxtecan (T-DXd), defining an additional treatment option for this sub-group. Regrettably, despite recent advances, the median survival of TNBC continues to lag far behind the approximately 5 years now expected for patients with ER-positive or HER2-positive breast cancers. We review the data supporting immunotherapy, ADCs, and targeted agents in subgroups of patients with TNBC, and current clinical trials that may pave the way to further advances in this challenging disease.

Dramatic Response to Pyrotinib and T-DM1 in HER2-Negative Metastatic Breast Cancer With 2 Activating HER2 Mutations

HER2 signaling is activated in response to somatic HER2 mutations, which are often found in invasive lobular breast cancer (ILC) and are associated with poor prognosis. Tyrosine kinase inhibitors (TKIs) have demonstrated considerable antitumor activity in patients with HER2-mutated advanced breast cancer (BC). Further, several clinical trials have indicated that HER2-targeted antibody-drug conjugates (ADCs) exhibit promising efficacy in lung cancer with HER2 mutations, and the efficacy of ADCs against HER2-mutated BC is currently being evaluated. Several preclinical studies have demonstrated that the therapeutic efficacy of ADCs in HER2-mutated cancer can be enhanced by the addition of irreversible TKIs, but the potential of such a combined treatment regimen for the treatment of HER2-mutated BC has not been reported. Herein, we describe a case in which a patient with estrogen receptor-positive/HER2-negative metastatic ILC with 2 activating HER2 mutations (D769H and V777L) exhibited a significant and durable response to anti-HER2 treatment with pyrotinib (an irreversible TKI) in combination with ado-trastuzumab emtansine, which was administered after multiple lines of therapy that had resulted in disease progression. Further, based on the evidence from the present case, TKI plus ADC seems to be a promising combination anti-HER2 regimen for patients with HER2-negative/HER2-mutated advanced BC, although further rigorous studies are warranted to confirm these findings.

Targeting HER2 alterations in non-small cell lung cancer: Therapeutic breakthrough and challenges

In non-small cell lung cancer (NSCLC) with human epidermal growth factor receptor 2 (HER2) alterations, chemotherapy remains the standard treatment over a decade, due to the minor efficacy of traditional pan-HER tyrosine kinase inhibitors (TKIs) and HER2-targeted monoclonal antibodies. In recent years, novel selective HER2 TKIs have been developed for pretreated HER2-mutant patients. In particular, pyrotinib has shown moderate efficacy as well as a manageable safety profile, and it is now being further evaluated as monotherapy or combined with other existing therapies; by contrast, while poziotinib has demonstrated promising preliminary results, the high rates of toxicity has hampered subsequent studies. Most notably, trastuzumab deruxtecan (T-DXd, DS-8201) has led to a significant breakthrough, with the most encouraging efficacy data (response rate of 55 %, median progression-free survival of 8.2 months and median overall survival of 17.8 months) among all the anti-HER2 agents. This is certainly remarkable progress, and T-DXd is undoubtedly the key drug for the treatment of this disease. Future developments regarding T-DXd are favourable, including shifting from monotherapy to combination strategies, improving structural design to optimise antitumour activity and minimise toxicity, identifying the potential resistance mechanisms and developing therapeutic strategies to overcome them. Several other challenges need to be addressed, such as the intracranial activity of anti-HER2 agents and the optimal sequencing of therapies. Here, we summarise recent therapeutic advances in targeting HER2 alterations in NSCLC and highlight the future perspectives of these patient populations.

Resistance to Antibody-Drug Conjugates Targeting HER2 in Breast Cancer: Molecular Landscape and Future Challenges

The treatment of HER2-positive metastatic breast cancer (mBC) with Trastuzumab emtansine (T-DM1) and Trastuzumab deruxtecan (T-DXd), two antibody-drug conjugates (ADCs) targeting HER2, is burdened by progression of disease related to the acquisition of mechanisms of resistance. Resistance to T-DM1 is caused by the decrease of HER2 expression, the alteration of intracellular trafficking, the impairment of lysosome functions, the drug expulsion through efflux pumps and the activation of alternative signal pathways. Instead, the decrease of HER2 expression and SLX4 loss of function mutations represent the first evidences of mechanisms of resistance to T-DXd, according to the results of DAISY trial. Several strategies are under evaluation to overcome resistances to anti-HER2 ADCs and improve clinical outcomes in patients progressing on these agents: combinations with tyrosine kinase inhibitors, statins, immune checkpoint inhibitors and synthetic DNA-damaging agents are emerging as promising approaches. Furthermore, novel anti-HER2 ADCs with innovative structures and mechanisms of action are in development, in the attempt to further improve the activity and tolerability of currently available agents.

Inhibition of mutationally activated HER2

Human epidermal growth factor receptor 2 (HER2) is an oncogenic driver and key therapeutic target for human cancers. Current therapies targeting HER2 are primarily based on overexpression of the wild-type form of HER2. However, kinase domain mutations have been identified that can increase the activity of HER2 even when expressed at basal levels. Using purified enzymes, we confirmed the hyperactivity of two HER2 mutants (D769Y and P780insGSP). To identify small molecule inhibitors against these cancer-associated variants, we used a combined approach consisting of biochemical testing, similarity-based searching, and in silico modeling. These approaches resulted in the identification of a candidate molecule that inhibits mutant forms of HER2 in vitro and in cell-based assays. Our structural model predicts that the compound takes advantage of water-mediated interactions in the HER2 kinase binding pocket.

Clinical implication of genetic composition and molecular mechanism on treatment strategies of HER2-positive breast cancers

The current clinical management model of HER2-positive breast cancers is commonly based on guidelines, which in turn are based on the design and outcome of clinical trials. While this model is useful to most practicing clinicians, the treatment outcome of individual patient is not certain at the start of treatment. As the understanding of the translational research of carcinogenesis and the related changes in cancer genetics and tumor microenvironment during treatment is critical in the selection of right choice of treatment to maximize the successful clinical outcome for the patient, this review article intends to discuss the latest developments in the genetic and molecular mechanisms of cancer progression and treatment resistance, and how they influence the planning of the treatment strategies of HER2-positive breast cancers.

Clinical value of next-generation sequencing in guiding decisions regarding endocrine therapy for advanced HR-positive/HER-2-negative breast cancer

OBJECTIVE

The mechanism of acquired gene mutation plays a major role in resistance to endocrine therapy in hormone receptor (HR)-positive advanced breast cancer. Circulating tumor DNA (ctDNA) has been allowed for the assessment of the genomic profiles of patients with advanced cancer. We performed this study to search for molecular markers of endocrine therapy efficacy and to explore the clinical value of ctDNA to guide precise endocrine therapy for HR-positive/human epidermal growth factor receptor-2 (HER-2)-negative metastatic breast cancer patients.

METHODS

In this open-label, multicohort, prospective study, patients were assigned to four parallel cohorts and matched according to mutations identified in ctDNA: 1) activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway preferred mTOR inhibitor combined with endocrine therapy; 2) estrogen receptor 1 (ESR1) mutation preferred fulvestrant; 3) HER-2 mutations preferred pyrotinib; and 4) no actionable mutations received treatment according to the clinical situation. In all cohorts, patients were divided into compliance group and violation group. The primary outcome measure was progression-free survival (PFS), and the secondary outcome measure was overall survival (OS).

RESULTS

In all cohorts, the combined median PFS was 4.9 months, and median PFS for the compliance and violation groups was 6.0 and 3.0 months, respectively [P=0.022, hazard ratio (HR)=0.57]. Multivariate Cox regression model showed the risk of disease progression was lower in compliance group than in violation group (P=0.023, HR=0.55). Among the patients with HER-2 mutations, the median PFS was 11.1 months in the compliance group and 2.2 months in the violation group (P=0.011, HR=0.20). There was no significant difference in the median PFS between patients who did and did not comply with the treatment protocol in patients with activation of the PI3K/AKT/mTOR or ESR1 mutation.

CONCLUSIONS

The results suggest that ctDNA may help to guide the optimal endocrine therapy strategy for metastatic breast cancer patients and to achieve a better PFS. Next-generation sequencing (NGS) detection could aid in distinguishing patients with HER-2 mutation and developing new treatment strategies.

A novel treatment strategy of HER2-targeted therapy in combination with Everolimus for HR+/HER2- advanced breast cancer patients with HER2 mutations

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Trastuzumab combined with Everolimus is an effective treatment for ER+/HER2-HER2-mutant breast cancer patients.

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HER2 mutant breast cancer cells are highly sensitive to the combination of HER2-targeted therapies and Everolimus.

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Lapatinib combined with Everolimus inhibits HER2 downstream signaling.

The incidence of HER2 somatic mutations in breast cancer is about 2–4%, mainly occurring in the HR+/HER2- subtype. Preclinical studies suggest that HER2 mutations can lead to constitutive HER2 activation, but effective treatment options for the clinical management of patients with HER2 mutations remain obscure. Our study analyzed HER2 mutation status by performing next-generation sequencing using tumor tissues and over 300 plasma samples from 72 metastatic breast cancer patients. We observed that two patients bearing HER2 mutations (Patient #1 bearing S310F and V777L mutations, Patient #2 bearing 778insGSP mutation) achieved a durable partial response to Trastuzumab combined with Everolimus. In vitro experiments showed that T47D and MCF7 cells overexpressing these HER2 mutants (S310F, V777L, 778insGSP and L755S) were sensitive to HER2-targeted therapies combined with the mTOR inhibitor Everolimus. These findings provide a treatment option for patients with HER2 mutations by combining HER2-targeted therapies with Everolimus.

Subclassifying triple-negative breast cancers and its potential clinical utility

The molecular subtyping of triple-negative breast cancer (TNBC) is critical to guiding individualized patient treatment. In this study, we sought to characterize the clinicopathologic features of TNBC subtypes and to identify correlates of patient survival in an effort to provide a robust foundation for treatment planning. We additionally assessed PD-L1 expression in Chinese TNBC patients and evaluated the relationship between such expression and immunotherapeutic treatment outcomes. Based on analyses of histologic characteristics including apocrine differentiation, tumor-infiltrating lymphocytes, and metaplastic features, we selected immunohistochemical (IHC) markers including CD8, FOXC1, and AR for use in classifying TNBC cases. Associations between these subtypes and a range of clinicopathologic characteristics were evaluated. We classified a cohort of 93 TNBC patients into individuals with luminal androgen receptor (LAR), immunomodulatory (IM), basal-like immune-suppressed (BLIS), and mesenchymal (MES) tumor subtypes (23, 24, 39, and 7 cases, respectively). PD-L1 positivity was observed in 49.6% of cases and was more common in individuals with IM subtype disease. Mismatch repair deficiency (dMMR) was observed in just one patient. Significant differences in histologic grade, pT stage, lymphocyte distribution patterns, large scarring areas without cells in tumor of central (central scar), and PD-L1, P53, and Rb status were observed among these TNBC subtypes, whereas no such differences were observed with respect to age, invasion pattern, or pN stage. Rates of disease progression were higher at the 40-50 month follow-up time point, but there were no significant differences in recurrence-free survival or breast cancer-specific survival among these subtypes. IHC markers associated with clinicopathologic characteristics represent a powerful approach to TNBC molecular typing, providing a foundation for precision patient treatment. PD-L1 expression may represent a relevant factor in TNBC patient immunotherapeutic treatment planning, whereas dMMR is not likely to be of substantial value when evaluating immunotherapeutic efficacy in these patients.

Response of Leptomeningeal Metastasis of Breast Cancer With a HER2/neu Activating Variant to Tucatinib: A Case Report

Metastatic breast cancer demonstrates HER2/neu amplification approximately 15% of the time. However, HER2 mutations, which often stimulate tumor growth, occur in only 3% to 5% of patients, and are seen more frequently in metastatic versus primary tumors. They are more frequent in lobular carcinoma, including triple-negative lobular cancer. Many of these variants are resistant to trastuzumab and lapatinib. However, neratinib can be efficacious, and recent data suggest that antibody-drug conjugates (ADCs) such as ado-trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan may also be helpful. Laboratory and clinical data raise the possibility that simultaneous treatment with ADCs plus neratinib may be even more efficacious. Tucatinib, which has demonstrated significant activity in the central nervous system, has also been shown in vitro to be active against a number of these HER2 variants. This report describes a patient with metastatic estrogen receptor-positive, HER2-nonamplified breast cancer with an activating HER2 mutation whose tumor became resistant to neratinib as well as capecitabine, but whose subsequent leptomeningeal disease had a dramatically successful response to tucatinib plus capecitabine. As the frequency of HER2 mutations increases during the evolution of metastatic breast cancer, it is important to obtain genomic evaluation on these tumors with either repeat tissue or liquid biopsy as they progress over time.

Role of ctDNA in Breast Cancer

Breast cancer is currently classified by immunohistochemistry. However, technological advances in the detection of circulating tumor DNA (ctDNA) have made new options available for diagnosis, classification, biological knowledge, and treatment selection. Breast cancer is a heterogeneous disease and ctDNA can accurately reflect this heterogeneity, allowing us to detect, monitor, and understand the evolution of the disease. Breast cancer patients have higher levels of circulating DNA than healthy subjects, and ctDNA can be used for different objectives at different timepoints of the disease, ranging from screening and early detection to monitoring for resistance mutations in advanced disease. In early breast cancer, ctDNA clearance has been associated with higher rates of complete pathological response after neoadjuvant treatment and with fewer recurrences after radical treatments. In metastatic disease, ctDNA can help select the optimal sequencing of treatments. In the future, thanks to new bioinformatics tools, the use of ctDNA in breast cancer will become more frequent, enhancing our knowledge of the biology of tumors. Moreover, deep learning algorithms may also be able to predict breast cancer evolution or treatment sensitivity. In the coming years, continued research and the improvement of liquid biopsy techniques will be key to the implementation of ctDNA analysis in routine clinical practice.

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

During recent years, a number of new compounds against HER2 have reached clinics, improving the prognosis and quality of life of HER2-positive breast cancer patients. Nonetheless, resistance to standard-of-care drugs has motivated the development of novel agents, such as new antibody-drug conjugates (ADCs). The latter are a group of drugs that benefit from the potency of cytotoxic agents whose action is specifically guided to the tumor by the target-specific antibody. Two anti-HER2 ADCs have reached the clinic: trastuzumab-emtansine and, more recently, trastuzumab-deruxtecan. In addition, several other HER2-targeted ADCs are in preclinical or clinical development, some of them with promising signs of activity. In the present review, the structure, mechanism of action, and potential resistance to all these ADCs will be described. Specific attention will be given to discussing novel strategies to circumvent resistance to ADCs.

Case Report: Effective Treatment With Pyrotinib and Capecitabine in a Heavily Pretreated Locally Advanced Breast Cancer Harboring Both HER2 Overexpression and Mutant

The prognosis for female patients with locally advanced breast cancer (LABC) has improved with the emergence of novel drugs, especially for those who have HER2 overexpression or ERBB-2 amplification. Trastuzumab-based regimen has been the paradigm in guidelines as first-line therapy, whereas many patients got progressive disease after several cycles of treatment or rapidly progress because of primary resistance. Point mutations of ERBB2 gene occur in both HER2-amplication and non-amplification patients, with a 2% ratio in HER2 non-amplification cohort and 1.48% in HER2 amplication population. The acquired mutation ratio of ERBB2 substantially raised to 16.7%–17.7% in patients prior to trastuzumab treatment. ERBB2 mutation may be a critical reason of resistance and disease progression among the patients treated with anti-HER2 monoclonal trastuzumab or dual anti-HER2 antibodies with trastuzumab and pertuzumab, or tyrosine-kinase inhibitor. ERBB-2 mutation with L755S and V842I indicates resistance to trastuzumab, while that with L755S and K753I indicates resistance to lapatinib; these mutations maybe sensitive to pan-HER tyrosine-kinase inhibitors. A 48-year woman diagnosed with HER2-positive LABC developed trastuzumab resistance after three lines of trastuzumab cross-line treatment with partial response (PR) as the best response. The tissue was performed by next-generation sequencing (NGS), and the results discovered L755S in ERBB2 gene. Then, she received effective treatment with pyrotinib plus capecitabine and underwent mastectomy after six cycles of combined treatment with PR. Subsequently, breast mastectomy was performed, and she took pyrotinib plus capecitabine for 1 year and pyrotinib monotherapy for another 1 year as adjuvant therapy and achieved a long-term clinical benefit. In conclusion, pyrotinib is a potential neoadjuvant agent for patients who are heavily pretreated and harbor both ERBB2 amplification and ERBB2 mutant in locally advanced breast cancer.

Large-scale genomic sequencing reveals adaptive opportunity of targeting mutated-PI3Kα in early and advanced HER2-positive breast cancer

BACKGROUND

Few studies have discussed the contradictory roles of mutated-PI3Kα in HER2-positive (HER2+) breast cancer. Thus, we characterised the adaptive roles of PI3Kα mutations among HER2+ tumour progression.

METHODS

We conducted prospective clinical sequencing of 1923 Chinese breast cancer patients and illustrated the clinical significance of PIK3CA mutations in locally advanced and advanced HER2+ cohort. A high-throughput PIK3CA mutations-barcoding screen was performed to reveal impactful mutation sites in tumour growth and drug responses.

RESULTS

PIK3CA mutations acted as a protective factor in treatment-naïve patients; however, advanced/locally advanced patients harbouring mutated-PI3Kα exhibited a higher progressive disease rate (100% vs. 15%, p = .000053) and a lower objective response rate (81.7% vs. 95.4%, p = .0008) in response to trastuzumab-based therapy. Meanwhile, patients exhibiting anti-HER2 resistance had a relatively high variant allele fraction (VAF) of PIK3CA mutations; we defined the VAF > 12.23% as a predictor of poor anti-HER2 neoadjuvant treatment efficacy. Pooled mutations screen revealed that specific PI3Kα mutation alleles mediated own biological effects. PIK3CA functional mutations suppressed the growth of HER2+ cells, but conferred anti-HER2 resistance, which can be reversed by the PI3Kα-specific inhibitor BYL719.

CONCLUSIONS

We proposed adaptive treatment strategies that the mutated PIK3CA and amplified ERBB2 should be concomitantly inhibited when exposing to continuous anti-HER2 therapy, while the combination of anti-HER2 and anti-PI3Kα treatment was not essential for anti-HER2 treatment-naïve patients. These findings improve the understanding of genomics-guided treatment in the different progressions of HER2+ breast cancer.

Biomarker Analysis of the Phase III NALA Study of Neratinib + Capecitabine versus Lapatinib + Capecitabine in Patients with Previously Treated Metastatic Breast Cancer

PURPOSE

Neratinib plus capecitabine (N+C) demonstrated significant progression-free survival (PFS) benefit in NALA (NCT01808573), a randomized phase III trial comparing N+C with lapatinib + capecitabine (L+C) in 621 patients with HER2-positive (HER2+) metastatic breast cancer (MBC) who had received ≥2 prior HER2-directed regimens in the metastatic setting. We evaluated correlations between exploratory biomarkers and PFS.

PATIENTS AND METHODS

Somatic mutations were evaluated by next-generation sequencing on primary or metastatic samples. HER2 protein expression was evaluated by central IHC, H-score, and VeraTag/HERmark. p95 expression (truncated HER2) was measured by VeraTag. HRs were estimated using unstratified Cox proportional hazards models.

RESULTS

Four hundred and twenty samples had successful sequencing: 34.0% had PIK3CA mutations and 5.5% had HER2 (ERBB2) mutations. In the combined patient populations, PIK3CA mutations trended toward shorter PFS [wild-type vs. mutant, HR = 0.81; 95% confidence interval (CI), 0.64-1.03], whereas HER2 mutations trended toward longer PFS [HR = 1.69 (95% CI, 0.97-3.29)]. Higher HER2 protein expression was associated with longer PFS [IHC 3+ vs. 2+, HR = 0.67 (0.54-0.82); H-score ≥240 versus <240, HR = 0.77 (0.63-0.93); HERmark positive vs. negative, HR = 0.76 (0.59-0.98)]. Patients whose tumors had higher HER2 protein expression (any method) derived an increased benefit from N+C compared with L+C [IHC 3+, HR = 0.64 (0.51-0.81); H-score ≥ 240, HR = 0.54 (0.41-0.72); HERmark positive, HR = 0.65 (0.50-0.84)], as did patients with high p95 [p95 ≥2.8 relative fluorescence (RF)/mm2, HR = 0.66 (0.50-0.86) vs. p95 < 2.8 RF/mm2, HR = 0.91 (0.61-1.36)].

CONCLUSIONS

PIK3CA mutations were associated with shorter PFS whereas higher HER2 expression was associated with longer PFS. Higher HER2 protein expression was also associated with a greater benefit for N+C compared with L+C.

Computational studies of anaplastic lymphoma kinase mutations reveal common mechanisms of oncogenic activation

High-risk tumors are genomically heterogeneous, harboring gene amplifications and mutations. The activation status of mutated proteins in cancer can profoundly impact disease progression, patient response, and drug sensitivity. Yet, outside of a few hotspot mutations, functional studies of clinically observed mutations are not commonly pursued. We report a combined experimental profiling and computational analysis of the effects of clinically observed and “test” mutations in the kinase domain of anaplastic lymphoma kinase (ALK), a known oncogenic driver in pediatric neuroblastoma. We find that the activation status of the mutated protein is a good indicator of the transforming ability in NIH 3T3 cells. We also report biophysical as well as data-driven models with predictive power to profile these mutant kinases in silico.

Kinases play important roles in diverse cellular processes, including signaling, differentiation, proliferation, and metabolism. They are frequently mutated in cancer and are the targets of a large number of specific inhibitors. Surveys of cancer genome atlases reveal that kinase domains, which consist of 300 amino acids, can harbor numerous (150 to 200) single-point mutations across different patients in the same disease. This preponderance of mutations—some activating, some silent—in a known target protein make clinical decisions for enrolling patients in drug trials challenging since the relevance of the target and its drug sensitivity often depend on the mutational status in a given patient. We show through computational studies using molecular dynamics (MD) as well as enhanced sampling simulations that the experimentally determined activation status of a mutated kinase can be predicted effectively by identifying a hydrogen bonding fingerprint in the activation loop and the αC-helix regions, despite the fact that mutations in cancer patients occur throughout the kinase domain. In our study, we find that the predictive power of MD is superior to a purely data-driven machine learning model involving biochemical features that we implemented, even though MD utilized far fewer features (in fact, just one) in an unsupervised setting. Moreover, the MD results provide key insights into convergent mechanisms of activation, primarily involving differential stabilization of a hydrogen bond network that engages residues of the activation loop and αC-helix in the active-like conformation (in >70% of the mutations studied, regardless of the location of the mutation).

Clinicopathologic features and treatment advances in cancers with HER2 alterations

HER2 is one of the most important proteins of the epidermal growth factor receptor (EGFR) family, whose alterations include amplification, overexpression and gene mutation. Growing attention has been given to HER2 as a biomarker for prognosis, an indicator for treatment response and a target for new drugs. Tumors with HER2 alterations have been well studied in multiple locations as distinct entities for treatment, especially breast cancer, gastric cancer, lung cancer and colorectal cancer. These four cancers are the leading causes of cancer incidence and cancer-related death worldwide. The present study details the landscape of HER2 amplification/overexpression and mutations and gives an up-to-date analysis of current clinical trials in the four cancers mentioned above. Different HER2-altered cancers not only respond differently to HER2-targeting therapies but also display diverse survival outcomes. Even in the same type of cancer, HER2 amplification/overexpression differs from HER2 mutation in terms of clinicopathologic features and treatment strategies. As an emerging strategy in cancer treatment, immune checkpoint inhibitors demonstrate distinct outcomes in HER2-altered breast cancer, gastric cancer and lung cancer.

Comparison of the sensitivity of Western blotting between PVDF and NC membranes

Western blotting (WB) is one of the most widely used techniques to identify proteins as well as post translational modifications of proteins. The selection of electroblotted membrane is one of the key factors affecting the detection sensitivity of the protein which is transferred from gel to membrane in WB. The most common used membranes are polyvinylidene fluoride (PVDF) and nitrocellulose (NC) membranes. Which membrane of these two is more suitable for WB has not been reported so far. Here, by incubating proteins which were transferred to PVDF or NC membranes with a series of antibodies and different types of lectins, we investigated the relationship between the binding ability of these two membranes to proteins or glycoproteins and the molecular weight of the target protein. The antibody re-probed ability of the two membranes was also explored. Moreover, we verified the above results by directly incubating proteins having different molecular weights onto PVDF or NC membranes. Bound proteins were stained with direct blue-71, and the staining intensity was quantitated by scanning and densitometry.

Breast cancer and DDT: putative interactions, associated gene alterations, and molecular pathways

The global burden of cancer has recorded an ever-increasing trend in the developing world. The GLOBOCAN, 2018 report has ranked breast cancer (BC) as the second (11.6%) most common form of cancer afflicting the female population worldwide. BC presents as a multi-factorial trait with numerous risk factors associated with the disease phenotype. Besides, genetic predisposition, exposure to environmental chemicals, and pollutants are considered to increase the magnitude of disease in susceptible individuals. Hence, the present observational study aims to investigate those proteins in the host which interact with the persistent organic pollutant, 2,4-dichlorodiphenyltrichloroethane (DDT), and associated alterations in genes encoding these proteins using a computational approach. The genetic alterations were ascertained using the Breast Invasive Carcinoma dataset available in the cBioportal database. The possible functional consequences of mutations identified in the selected dataset were further assessed using tools such as I-Mutant and PROVEAN. The ERBB2 (14%) and FASLG (10%) genes were found to harbor the highest frequency of gene alterations. Gene amplification and deep deletions were the most commonly observed alteration in almost all the genes investigated. Additionally, several synonymous, non-synonymous, frameshift, splice site mutations were also documented. The gnomAD analysis revealed three polymorphic variants in HTR2A (rs539430264), ESR2 (rs905821436), and CYP2B6 (rs757834610), all of which had a minor allele frequency < 0.01. Population-wide screening of observed gene alterations can provide clues on the putative association of these gross and single nucleotide substitutions with the pathophysiology and progression of breast cancer. Experimental genotyping and functional analysis of mutations is warranted to further prove the adverse effects of organochlorine compounds on female health.

Rac inhibition as a novel therapeutic strategy for EGFR/HER2 targeted therapy resistant breast cancer

Background

Even though targeted therapies are available for cancers expressing oncogenic epidermal growth receptor (EGFR) and (or) human EGFR2 (HER2), acquired or intrinsic resistance often confounds therapy success. Common mechanisms of therapy resistance involve activating receptor point mutations and (or) upregulation of signaling downstream of EGFR/HER2 to Akt and (or) mitogen activated protein kinase (MAPK) pathways. However, additional pathways of resistance may exist thus, confounding successful therapy.

Methods

To determine novel mechanisms of EGFR/HER2 therapy resistance in breast cancer, gefitinib or lapatinib resistant variants were created from SKBR3 breast cancer cells. Syngenic therapy sensitive and resistant SKBR3 variants were characterized for mechanisms of resistance by mammosphere assays, viability assays, and western blotting for total and phospho proteins.

Results

Gefitinib and lapatinib treatments reduced mammosphere formation in the sensitive cells, but not in the therapy resistant variants, indicating enhanced mesenchymal and cancer stem cell-like characteristics in therapy resistant cells. The therapy resistant variants did not show significant changes in known therapy resistant pathways of AKT and MAPK activities downstream of EGFR/HER2. However, these cells exhibited elevated expression and activation of the small GTPase Rac, which is a pivotal intermediate of GFR signaling in EMT and metastasis. Therefore, the potential of the Rac inhibitors EHop-016 and MBQ-167 to overcome therapy resistance was tested, and found to inhibit viability and induce apoptosis of therapy resistant cells.

Conclusions

Rac inhibition may represent a viable strategy for treatment of EGFR/HER2 targeted therapy resistant breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08366-7.

Partial Response to Pyrotinib Plus Capecitabine in an Advanced Breast Cancer Patient with HER2 Amplification and R157W Mutation After Anti-HER2 Treatment: A Case Report and Literature Review

Human epidermal growth factor receptor2 (HER2) overexpression/amplification is associated with high malignancy, rapid disease progression and poor overall survival in breast cancer. The application of anti-HER2 drugs has greatly improved the survival of patients with HER2-positive breast cancer, but drug resistance issues affect the long-term efficacy. The HER2 mutation is considered to be one of the reasons for resistance to anti-HER2 therapy, and there is currently no standard treatment. We report for the first time the detection of HER2 amplification with R157W mutation by second-generation sequencing (NGS) in a 57-year-old hormone receptor-negative, HER2-positive woman with advanced breast cancer who was resistant to multi-line anti-HER2 therapies. She subsequently received pyrotinib combined with capecitabine treatment and achieved partial response. The small-molecule pan-HER family irreversible inhibitor pyrotinib combined with capecitabine has shown a promising effect in the treatment of HER2 mutation-induced resistance, but the molecular mechanism and efficacy need to be further verified.

Effects of Ado-Trastuzumab Emtansine and Fam-Trastuzumab Deruxtecan on Metastatic Breast Cancer Harboring HER2 Amplification and the L755S Mutation

Somatic mutations in human epidermal growth factor receptor 2 (HER2) are present in approximately 3% of breast cancers. Some HER2 mutations are activating, and they represent a mechanism of resistance to conventional anti-HER2 therapies such as trastuzumab and lapatinib. Consistently, in patients with HER2-amplified breast cancer, these mutations are predominantly observed in metastatic tumors obtained after exposure to anti-HER2 systemic therapies, possibly after clonal selection. Therefore, it is rare to find coexistent HER2 mutation and amplification in the early clinical course, and thus, the clinical relevance of HER2 mutation to the sensitivity to HER2-targeted drugs, particularly antibody-drug conjugates (ADCs) such as ado-trastuzumab emtansine (T-DM1) and the recently approved fam-trastuzumab deruxtecan (T-DXd), remains unclear. In this article, we describe a patient with de novo metastatic breast cancer who exhibited both HER2 amplification and the L755S mutation in the untreated primary breast tumor obtained at the initial diagnosis, and the lesion responded to T-DM1 and T-DXd after exhibiting clinical resistance to other HER2-targeted drugs. Our current case findings suggested that anti-HER2 ADCs should be prioritized over conventional trastuzumab- or lapatinib-based therapies for patients with HER2-amplified and comutated tumors. KEY POINTS: Although HER2 mutations were implicated in resistance to anti-HER2 monoclonal antibodies or HER2 tyrosine kinase inhibitors in preclinical studies, their clinical impact on sensitivity to anti-HER2 drugs is unclear owing to the rarity of concomitant HER2 mutation and HER2 amplification. A case of de novo metastatic breast cancer harboring both HER2 amplification and the L755S mutation in an untreated breast primary tumor displayed clinical resistance to standard trastuzumab- or lapatinib-based therapies but good responses to ado-trastuzumab emtansine (T-DM1) and fam-trastuzumab deruxtecan (T-DXd). Anti-HER2 antibody-drug conjugates such as T-DM1 and T-DXd may be prioritized over conventional trastuzumab- or lapatinib-containing therapies for patients with HER2-amplified and comutated tumors.

Molecular landscape and efficacy of HER2-targeted therapy in patients with HER2-mutated metastatic breast cancer

Human epidermal growth factor receptor 2 (HER2) protein overexpression or gene amplification is an important predictive biomarker for identifying patients with breast cancer, who may benefit from HER2-targeted therapy. However, little is known about the molecular landscape and efficacy of HER2-targeted therapy in patients with HER2-mutated metastatic breast cancer. We analysed the HER2 mutation features of 1184 patients with invasive breast cancer. In addition, a single-arm, prospective, phase-II study (NCT03412383) of pyrotinib was conducted in patient with metastatic HER2 amplification-negative, mutation-positive breast cancer. Peripheral blood was collected from each patient and circulating tumour DNA (ctDNA) sequencing was performed using a 1021 gene panel. HER2 mutations were detected in 8.9% (105/1184) of patients. The HER2 amplification-positive patients had a higher mutation frequency than the HER2 amplification-negative patients (19.5% vs. 4.8%, P < 0.001). A multivariate Cox regression analysis indicated that patients with HER2 mutations had a shorter progression-free survival (PFS) than HER2 wild-type patients (median PFS 4.7 months vs. 11.0 months, hazard ratio 2.65, 95% confidence interval 1.25-5.65, P = 0.011). Ten HER2 amplification-negative, mutation-positive patients who received pyrotinib monotherapy were ultimately included in the efficacy analysis. The median PFS was 4.9 months. The objective response rate (complete response + partial response) was 40.0% and the clinical benefit rate (complete response + partial response + stable disease over 24 weeks) was 60%. In conclusion, a HER2 gene mutation analysis is potentially useful to identify biomarkers of trastuzumab resistance in HER2 amplification-positive patients. Patients with HER2-mutated, non-amplified metastatic breast cancers may benefit from pyrotinib.

The deubiquitylase USP2 maintains ErbB2 abundance via counteracting endocytic degradation and represents a therapeutic target in ErbB2-positive breast cancer

ErbB2 overexpression identifies a subclass of breast cancer as ErbB2-positive that is frequently associated with poor prognosis. Current ErbB2-targeted therapies have profoundly improved patient outcomes, but mutations occurring in ErbB2 have been shown to confer drug resistance. Induction of ErbB2 degradation was proposed as an intriguing strategy to battle with ErbB2-positive breast cancer and reduced mutation-incurred drug resistance. Although multiple HSP90 inhibitors have been demonstrated to effectively trigger ErbB2 degradation, none succeeded in the clinical evaluations. To develop novel ErbB2-targeting strategies, we investigated the endocytic degradation and reversible ubiquitylation of ErbB2 in breast cancer. In this study, we reveal that HSP90 inhibition leads to efficient ubiquitylation and endocytic degradation of ErbB2 through the canonical endo-lysosomal route. USP2 associates with internalized ErbB2 and prevents its lysosomal sorting and degradation via exerting deubiquitylase activity. Accordingly, the USP2 inhibitor ML364 is capable of inducing ErbB2 ubiquitylation and accelerating its turnover. ML364 potentiates the pro-degradation effects of HSP90 inhibitors on ErbB2 and hence sensitizes ErbB2-positive breast cancer cells to HSP90 inhibition. The combination of USP2 and HSP90 inhibitors effectively restrains ErbB2-positive breast cancer xenograft growth in vivo. Based on these observations, we conclude that USP2 safeguards ErbB2 surface levels by antagonizing its ubiquitylation-mediated endocytic degradation, which can be exploited to design novel therapeutic strategies against ErbB2-driven malignancies as combinatorial treatment with HSP90 inhibitors.

Targeting Rac and Cdc42 GEFs in Metastatic Cancer

The Rho family GTPases Rho, Rac, and Cdc42 have emerged as key players in cancer metastasis, due to their essential roles in regulating cell division and actin cytoskeletal rearrangements; and thus, cell growth, migration/invasion, polarity, and adhesion. This review will focus on the close homologs Rac and Cdc42, which have been established as drivers of metastasis and therapy resistance in multiple cancer types. Rac and Cdc42 are often dysregulated in cancer due to hyperactivation by guanine nucleotide exchange factors (GEFs), belonging to both the diffuse B-cell lymphoma (Dbl) and dedicator of cytokinesis (DOCK) families. Rac/Cdc42 GEFs are activated by a myriad of oncogenic cell surface receptors, such as growth factor receptors, G-protein coupled receptors, cytokine receptors, and integrins; consequently, a number of Rac/Cdc42 GEFs have been implicated in metastatic cancer. Hence, inhibiting GEF-mediated Rac/Cdc42 activation represents a promising strategy for targeted metastatic cancer therapy. Herein, we focus on the role of oncogenic Rac/Cdc42 GEFs and discuss the recent advancements in the development of Rac and Cdc42 GEF-interacting inhibitors as targeted therapy for metastatic cancer, as well as their potential for overcoming cancer therapy resistance.

Towards personalized treatment for early stage HER2-positive breast cancer

Advances in HER2-targeted therapies have improved the survival of patients with HER2-positive breast cancer. The standard-of-care treatment for localized disease has been chemotherapy and 1 year of adjuvant HER2-targeted therapy, typically with the anti-HER2 antibody trastuzumab. Despite the effectiveness of this treatment, disease relapse occurs in a subset of patients; thus, focus has been placed on escalating treatment by either combining different HER2-targeted agents or extending the duration of HER2-targeted therapy. Indeed, dual HER2-targeted therapies and extended-duration anti-HER2 therapy, as well as adjuvant therapy with the anti-HER2 antibody-drug conjugate T-DM1, have all been approved for clinical use. Emerging evidence suggests, however, that some patients do not derive sufficient benefit from these additional therapies to offset the associated toxicities and/or costs. Similarly, the universal use of chemotherapy might not benefit all patients, and treatment de-escalation through omission of chemotherapy has shown promise in clinical trials and is currently being explored further. The future of precision medicine should therefore involve tailoring of therapy based on the genetics and biology of each tumour and the clinical characteristics of each patient. Predictive biomarkers that enable the identification of patients who will benefit from either escalated or de-escalated treatment will be crucial to this approach. In this Review, we summarize the available HER2-targeted agents and associated mechanisms of resistance, and describe the current therapeutic landscape of early stage HER2-positive breast cancer, focusing on strategies for treatment escalation or de-escalation.

Somatic Mutations in HER2 and Implications for Current Treatment Paradigms in HER2-Positive Breast Cancer

In one of every four or five cases of breast cancer, the human epidermal growth factor receptor-2 (HER2) gene is overexpressed. These carcinomas are known as HER2-positive. HER2 overexpression is linked to an aggressive phenotype and a lower rate of disease-free and overall survival. Drugs such as trastuzumab, pertuzumab, lapatinib, neratinib, and the more recent afatinib target the deregulation of HER2 expression. Some authors have attributed somatic mutations in HER2, a role in resistance to anti-HER2 therapy as differential regulation of HER2 has been observed among patients. Recently, studies in metastatic ER + tumors suggest that some HER2 mutations emerge as a mechanism of acquired resistance to endocrine therapy. In an effort to identify possible biomarkers of the efficacy of anti-HER2 therapy, we here review the known single-nucleotide polymorphisms (SNPs) of the HER2 gene found in HER2-positive breast cancer patients and their relationship with clinical outcomes. Information was recompiled on 11 somatic HER2 SNPs. Seven polymorphisms are located in the tyrosine kinase domain region of the gene contrasting with the low number of mutations found in extracellular and transmembrane areas. HER2-positive patients carrying S310F, S310Y, R678Q, D769H, or I767M mutations seem good candidates for anti-HER2 therapy as they show favorable outcomes and a good response to current pharmacological treatments. Carrying the L755S or D769Y mutation could also confer benefits when receiving neratinib or afatinib. By contrast, patients with mutations L755S, V842I, K753I, or D769Y do not seem to benefit from trastuzumab. Resistance to lapatinib has been reported in patients with L755S, V842I, and K753I. These data suggest that exploring HER2 SNPs in each patient could help individualize anti-HER2 therapies. Advances in our understanding of the genetics of the HER2 gene and its relations with the efficacy of anti-HER2 treatments are needed to improve the outcomes of patients with this aggressive breast cancer.

Evolving concepts in HER2 evaluation in breast cancer: Heterogeneity, HER2-low carcinomas and beyond

The human epidermal growth factor receptor 2 (HER2) is a well-known negative prognostic factor in breast cancer and a target of the monoclonal antibody trastuzumab as well as of other anti-HER2 compounds. Pioneering works on HER2-positive breast cancer in the 90s' launched a new era in clinical research and oncology practice that has reshaped the natural history of this disease. In diagnostic pathology the HER2 status is routinely assessed by using a combination of immunohistochemistry (IHC, to evaluate HER2 protein expression levels) and in situ hybridization (ISH, to assess HER2 gene status). For this purpose, international recommendations have been developed by a consensus of experts in the field, which have changed over the years according to new experimental and clinical data. In this review article we will document the changes that have contributed to a better evaluation of the HER2 status in clinical practice, furthermore we will discuss HER2 heterogeneity defined by IHC and ISH as well as by transcriptomic analysis and we will critically describe the complexity of HER2 equivocal results. Finally, we will introduce the clinical impact of HER2 mutations and we will define the upcoming category of HER2-low breast cancer with respect to emerging clinical data on the efficacy of specific anti-HER2 agents in subgroups of breast carcinomas lacking the classical oncogene addition dictated by HER2 amplification.

Current concepts in breast cancer genomics: An evidence based review by the CGC breast cancer working group

BACKGROUND

Genomic abnormalities in breast cancer have been described according to diverse conceptual frameworks, including histologic subtypes, clinical molecular subtypes, intrinsic DNA, RNA, and epigenetic profiles, and activated molecular pathways.

METHODS

The Cancer Genomics Consortium (CGC) Breast Cancer Workgroup performed an evidence based literature review to summarize current knowledge of clinically significant genomic alterations in breast cancer using CGC levels of evidence. Targetable or disease-defining alterations were prioritized.

RESULTS

We summarized genomic alterations in breast cancer within a framework of existing clinical tools for diagnosis, risk stratification, and therapeutic management. Using CGC levels of evidence, we catalog copy number profiles, gene expression profiles, and mutations in clinically significant genes. We also describe emerging molecular markers such as methylation profiling and immunotherapy biomarkers.

CONCLUSION

A summary of currently available information on breast cancer genomics will enhance precision medicine by serving as an interpretive resource for clinical laboratory geneticists, providing a foundation for future practice guidelines, and identifying knowledge gaps to address in future research.

Therapeutic applications of CRISPR/Cas9 in breast cancer and delivery potential of gold nanomaterials

Globally, approximately 1 in 4 cancers in women are diagnosed as breast cancer (BC). Despite significant advances in the diagnosis and therapy BCs, many patients develop metastases or relapses. Hence, novel therapeutic strategies are required, that can selectively and efficiently kill malignant cells. Direct targeting of the genetic and epigenetic aberrations that occur in BC development is a promising strategy to overcome the limitations of current therapies, which target the tumour phenotype. The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system, composed of only an easily modifiable single guide RNA (sgRNA) sequence bound to a Cas9 nuclease, has revolutionised genome editing due to its simplicity and efficiency compared to earlier systems. CRISPR/Cas9 and its associated catalytically inactivated dCas9 variants facilitate the knockout of overexpressed genes, correction of mutations in inactivated genes, and reprogramming of the epigenetic landscape to impair BC growth. To achieve efficient genome editing in vivo, a vector is required to deliver the components to target cells. Gold nanomaterials, including gold nanoparticles and nanoclusters, display many advantageous characteristics that have facilitated their widespread use in theranostics, as delivery vehicles, and imaging and photothermal agents. This review highlights the therapeutic applications of CRISPR/Cas9 in treating BCs, and briefly describes gold nanomaterials and their potential in CRISPR/Cas9 delivery.

Identification of an Activating Mutation in the Extracellular Domain of HER2 Conferring Resistance to Pertuzumab

Background

The aberrant expression of HER2 is highly associated with tumour occurrence and metastasis, therefore HER2 is extensively targeted for tumour immunotherapy. For example, trastuzumab and pertuzumab are FDA-approved monoclonal antibodies that target HER2-positive tumour cells. Despite their advances in clinical applications, emerging resistance to these two HER2-targeting antibodies has hindered their further application. Somatic mutations in HER2 receptor have been identified as one of the major reasons for resistance to anti-HER2 antibodies.

Methods

We analysed the frequency of somatic mutations in various tumour types based on TCGA and COSMIC databases. Then, the effect of the most frequent mutation (S310F) on the interaction between pertuzumab and HER2 was analysed by molecular modelling analysis. The effect of the S310F mutation was further evaluated through multiple in vitro binding experiments and antitumour activity assays.

Results

We found through bioinformatics analysis that S310F, an activating mutation in the HER2 extracellular domain, was the most frequent mutation in HER2. The S310F mutation was shown to confer resistance of HER2-positive tumour cells to pertuzumab treatment. With molecular modelling analysis, we confirmed the possibility that the S310F mutation might disrupt the interaction between pertuzumab and HER2 as a result of a significant change in the critical residue S310. Further functional analyses revealed that the S310F mutation completely abolished pertuzumab binding to HER2 receptor and inhibited pertuzumab antitumour efficacy.

Conclusion

We demonstrated the loss-of-function mechanism underlying pertuzumab resistance in HER2-positive tumour cells bearing the S310F mutation.

Efficacy and Determinants of Response to HER Kinase Inhibition in HER2-Mutant Metastatic Breast Cancer

HER2 mutations define a subset of metastatic breast cancers with a unique mechanism of oncogenic addiction to HER2 signaling. We explored activity of the irreversible pan-HER kinase inhibitor neratinib, alone or with fulvestrant, in 81 patients with HER2-mutant metastatic breast cancer. Overall response rate was similar with or without estrogen receptor (ER) blockade. By comparison, progression-free survival and duration of response appeared longer in ER⁺ patients receiving combination therapy, although the study was not designed for direct comparison. Preexistent concurrent activating HER2 or HER3 alterations were associated with poor treatment outcome. Similarly, acquisition of multiple HER2-activating events, as well as gatekeeper alterations, were observed at disease progression in a high proportion of patients deriving clinical benefit from neratinib. Collectively, these data define HER2 mutations as a therapeutic target in breast cancer and suggest that coexistence of additional HER signaling alterations may promote both de novo and acquired resistance to neratinib. SIGNIFICANCE: HER2 mutations define a targetable breast cancer subset, although sensitivity to irreversible HER kinase inhibition appears to be modified by the presence of concurrent activating genomic events in the pathway. These findings have implications for potential future combinatorial approaches and broader therapeutic development for this genomically defined subset of breast cancer.This article is highlighted in the In This Issue feature, p. 161.

The HER2 S310F Mutant Can Form an Active Heterodimer with the EGFR, Which Can Be Inhibited by Cetuximab but Not by Trastuzumab as well as Pertuzumab

G309 or S310 mutations on the HER2 extracellular domain II induce receptor activation. Clinically, S310F is most frequent among HER2 extracellular domain mutations and patients with the S310F mutation without HER2 amplification responded to trastuzumab with or without the pertuzumab combination. However, the ability of S310F mutant to form homodimers or heterodimers with wild-type HER2 and other HER receptors, or their reactivity to trastuzumab and pertuzumab treatments, has not been reported. We overexpressed S310F as well as G309A, G309E and S310Y HER2 mutants and tested their reactivity to trastuzumab and pertuzumab. All mutants reacted to trastuzumab, but S310F mutant did not react to pertuzumab along with S310Y or G309E mutants. Thereafter, we tested the effects of trastuzumab and pertuzumab on 5637 cell line expressing both wild-type HER2 and S310F mutant. The ligand-independent HER2 homodimerization blocking antibody, trastuzumab, did not inhibit the activation of the HER2 receptor, suggesting that the S310F HER2 mutant did not form homodimers or heterodimers with wild-type HER2. Because 5637 cells overexpressed the EGFR, the effects of cetuximab and gefitinib were determined, and both inhibited the activation of HER2 and significantly reduced cell growth. Because pertuzumab did not inhibit the phosphorylation of HER2 while it bound to wild-type HER2, EGFR-mediated phosphorylation is expected to occur on the S310F mutant. To confirm whether the S310F mutant HER2 retained its affinity to the EGFR, single molecule interaction analyses using TIRF microscopy were performed, which showed that S310F mutant successfully formed complexes with EGFR. In conclusion, HER2 S310F mutant can form an active heterodimer with the EGFR and it can be inhibited by cetuximab, but not by trastuzumab in combination with pertuzumab.

Emergence of ERBB2 Mutation as a Biomarker and an Actionable Target in Solid Cancers

The oncogenic role ERBB2 amplification is well established in breast and gastric cancers. This has led to the development of a well-known portfolio of monoclonal antibodies and kinase inhibitors targeting the ERBB2 kinase. More recently, activating mutations in the ERBB2 gene have been increasingly reported in multiple solid cancers and were shown to play an oncogenic role similar to that of ERBB2 amplification. Thus, ERBB2 mutations define a distinct molecular subtype of solid tumors and serve as actionable targets. However, efforts to target ERBB2 mutation has met with limited clinical success, possibly because of their low frequency, inadequate understanding of the biological activity of these mutations, and difficulty in separating the drivers from the passenger mutations. Given the current impetus to deliver molecularly targeted treatments for cancer, there is an important need to understand the therapeutic potential of ERBB2 mutations. Here we review the distribution of ERBB2 mutations in different tumor types, their potential as a novel biomarker that defines new subsets in many cancers, and current data on preclinical and clinical efforts to target these mutations. IMPLICATIONS FOR PRACTICE: A current trend in oncology is to identify novel genomic drivers of solid tumors and developing precision treatments that target them. ERBB2 amplification is an established therapeutic target in breast and gastric cancers, but efforts to translate this finding to other solid tumors with ERBB2 amplification have not been effective. Recently the focus has turned to targeting activating ERBB2 mutations. The year 2018 marked an important milestone in establishing ERBB2 mutation as an important actionable target in multiple cancer types. There have been several recent preclinical and clinical studies evaluating ERBB2 mutation as a therapeutic target with varying success. With increasing access to next-generation sequencing technologies in the clinic, oncologists are frequently identifying activating ERBB2 mutations in patients with cancer. There is a significant need both from the clinician and bench scientist perspectives to understand the current state of affairs for ERBB2 mutations.

Computational algorithms for in silico profiling of activating mutations in cancer

Methods to catalog and computationally assess the mutational landscape of proteins in human cancers are desirable. One approach is to adapt evolutionary or data-driven methods developed for predicting whether a single-nucleotide polymorphism (SNP) is deleterious to protein structure and function. In cases where understanding the mechanism of protein activation and regulation is desired, an alternative approach is to employ structure-based computational approaches to predict the effects of point mutations. Through a case study of mutations in kinase domains of three proteins, namely, the anaplastic lymphoma kinase (ALK) in pediatric neuroblastoma patients, serine/threonine-protein kinase B-Raf (BRAF) in melanoma patients, and erythroblastic oncogene B 2 (ErbB2 or HER2) in breast cancer patients, we compare the two approaches above. We find that the structure-based method is most appropriate for developing a binary classification of several different mutations, especially infrequently occurring ones, concerning the activation status of the given target protein. This approach is especially useful if the effects of mutations on the interactions of inhibitors with the target proteins are being sought. However, many patients will present with mutations spread across different target proteins, making structure-based models computationally demanding to implement and execute. In this situation, data-driven methods-including those based on machine learning techniques and evolutionary methods-are most appropriate for recognizing and illuminate mutational patterns. We show, however, that, in the present status of the field, the two methods have very different accuracies and confidence values, and hence, the optimal choice of their deployment is context-dependent.

HER2-L755S mutation induces hyperactive MAPK and PI3K-mTOR signaling, leading to resistance to HER2 tyrosine kinase inhibitor treatment

L755S, a HER2 kinase domain mutation, is the most common HER2 mutation in breast cancer associated with resistance to anti-HER2 trastuzumab treatment. Here, we showed that HER2-L755S confers hyperactivation of MAPK and PI3K/AKT/mTOR pathways and resistance to both reversible and irreversible HER2 tyrosine kinase inhibitors. We further demonstrated that the HER2 TKIs in combination with MEK inhibitor, AZD6244, or PI3K inhibitor, GDC0941, yield robust killing in HER2-L755S cancer cells, indicating a novel targeted strategy to overcome HER2-L755S resistance to anti-HER2 treatment.

Preclinical Characteristics of the Irreversible Pan-HER Kinase Inhibitor Neratinib Compared with Lapatinib: Implications for the Treatment of HER2-Positive and HER2-Mutated Breast Cancer

An estimated 15–20% of breast cancers overexpress human epidermal growth factor receptor 2 (HER2/ERBB2/neu). Two small-molecule tyrosine kinase inhibitors (TKIs), lapatinib and neratinib, have been approved for the treatment of HER2-positive (HER2+) breast cancer. Lapatinib, a reversible epidermal growth factor receptor (EGFR/ERBB1/HER1) and HER2 TKI, is used for the treatment of advanced HER2+ breast cancer in combination with capecitabine, in combination with trastuzumab in patients with hormone receptor-negative metastatic breast cancer, and in combination with an aromatase inhibitor for the first-line treatment of HER2+ breast cancer. Neratinib, a next-generation, irreversible pan-HER TKI, is used in the US for extended adjuvant treatment of adult patients with early-stage HER2+ breast cancer following 1 year of trastuzumab. In Europe, neratinib is used in the extended adjuvant treatment of adult patients with early-stage hormone receptor-positive HER2+ breast cancer who are less than 1 year from the completion of prior adjuvant trastuzumab-based therapy. Preclinical studies have shown that these agents have distinct properties that may impact their clinical activity. This review describes the preclinical characterization of lapatinib and neratinib, with a focus on the differences between these two agents that may have implications for patient management.

A significant response to a combination of trastuzumab and vinorelbine in HER2-negative metastatic breast cancer with HER2 V777L mutation

Metastatic breast cancer (MBC) is the most life-threatening disease in women worldwide. HER2-mutated breast carcinoma has been reported to benefit from HER2-targeted tyrosine kinase inhibitors recently. Here, we presented a heavy pretreated and harbored HER2 V777L mutation de novo stage IV Luminal B (HER2 unamplified) breast cancer patient who achieved an unexpected good response to trastuzumab combined with vinorelbine therapy. Although HER2-unamplified MBC patients do not regularly benefit from anti-HER2 target therapy, HER2 V777L mutation detected by next-generation sequencing from ctDNA may present as a predictive biomarker for anti-HER2-based strategy therapy in HER2-negative MBC patients.

Genomic and Transcriptomic Landscape of Triple-Negative Breast Cancers: Subtypes and Treatment Strategies

We comprehensively analyzed clinical, genomic, and transcriptomic data of a cohort of 465 primary triple-negative breast cancer (TNBC). PIK3CA mutations and copy-number gains of chromosome 22q11 were more frequent in our Chinese cohort than in The Cancer Genome Atlas. We classified TNBCs into four transcriptome-based subtypes: (1) luminal androgen receptor (LAR), (2) immunomodulatory, (3) basal-like immune-suppressed, and (4) mesenchymal-like. Putative therapeutic targets or biomarkers were identified among each subtype. Importantly, the LAR subtype showed more ERBB2 somatic mutations, infrequent mutational signature 3 and frequent CDKN2A loss. The comprehensive profile of TNBCs provided here will serve as a reference to further advance the understanding and precision treatment of TNBC.

Molecular Landscape of ERBB2/ERBB3 Mutated Colorectal Cancer

Background

Despite growing therapeutic relevance of ERBB2 amplifications in colorectal cancer (CRC), little is known about ERBB2/ERBB3 mutations. We aimed to characterize these subsets of CRC.

Methods

We performed a retrospective analysis of 419 CRC patients from MD Anderson (MDACC) and 619 patients from the Nurses' Health Study (NHS)/Health Professionals Follow-Up Study (HPFS) with tissue sequencing, clinicopathologic, mutational, and consensus molecular subtype (CMS) profiles of ERBB2/ERBB3 mutant patients. A third cohort of 1623 CRC patients with ctDNA assays characterized the ctDNA profile of ERBB2 mutants. All statistical tests were two-sided.

Results

ERBB2 mutations occurred in 4.1% (95% confidence interval [CI] = 2.4% to 6.4%), 5.8% (95% CI = 4.1% to 8.0%), and 5.1% (95% CI = 4.0% to 6.2%) of MDACC, NHS/HPFS, and ctDNA patients, respectively. ERBB3 mutations occurred in 5.7% (95% CI = 3.7% to 8.4%, 95% CI = 4.0% to 7.8%) of patients in both tissue cohorts. Age, stage, and tumor location were not associated with either mutation. Microsatellite instability (MSI) was associated with ERBB2 (odds ratio [OR] = 5.98, 95% CI = 2.47 to 14.49, P < .001; OR = 5.13, 95% CI = 2.38 to 11.05, P < .001) and ERBB3 mutations (OR = 3.48, 95% CI = 1.51 to 8.02, P = .002; OR = 3.40, 95% CI = 1.05 to 10.96, P = .03) in both tissue cohorts. Neither gene was associated with TP53, APC, KRAS, NRAS, or BRAF mutations in tissue. However, PIK3CA mutations were strongly associated with ERBB2 mutations in all three cohorts (OR = 3.68, 95% CI = 1.83 to 7.41, P = .001; OR = 2.25, 95% CI = 1.11 to 4.58, P = .02; OR = 2.11, 95% CI = 1.25 to 3.58, P = .004) and ERBB3 mutations in the MDACC cohort (OR = 13.26, 95% CI = 5.27 to 33.33, P < .001). ERBB2 (P = 0.08) and ERBB3 (P = .008) mutations were associated with CMS1 subtype. ERBB2 (hazard ratio [HR] = 1.82, 95% CI = 1.23 to 4.03, P = .009), but not ERBB3 (HR = 0.88, 95% CI = 0.45 to 1.73, P = .73), mutations were associated with worse overall survival.

Conclusions

MSI and PIK3CA mutations are associated with ERBB2/ERBB3 mutations. Co-occurring PIK3CA mutations may represent a second hit to oncogenic signaling that needs consideration when targeting ERBB2/ERBB3.

Neratinib is effective in breast tumors bearing both amplification and mutation of ERBB2 (HER2)

Mutations in ERBB2, the gene encoding epidermal growth factor receptor (EGFR) family member HER2, are common in and drive the growth of "HER2-negative" (not ERBB2 amplified) tumors but are rare in "HER2-positive" (ERBB2 amplified) breast cancer. We analyzed DNA-sequencing data from HER2-positive patients and used cell lines and a patient-derived xenograft model to test the consequence of HER2 mutations on the efficacy of anti-HER2 agents such as trastuzumab, lapatinib, and neratinib, an irreversible pan-EGFR inhibitor. HER2 mutations were present in ~7% of HER2-positive tumors, all of which were metastatic but not all were previously treated. Compared to HER2 amplification alone, in both patients and cultured cell lines, the co-occurrence of HER2 mutation and amplification was associated with poor response to trastuzumab and lapatinib, the standard-of-care anti-HER2 agents. In mice, xenografts established from a patient whose HER2-positive tumor acquired a D769Y mutation in HER2 after progression on trastuzumab-based therapy were resistant to trastuzumab or lapatinib but were sensitive to neratinib. Clinical data revealed that six heavily pretreated patients with tumors bearing coincident HER2 amplification and mutation subsequently exhibited a statistically significant response to neratinib monotherapy. Thus, these findings indicate that coincident HER2 mutation reduces the efficacy of therapies commonly used to treat HER2-positive breast cancer, particularly in metastatic and previously HER2 inhibitor-treated patients, as well as potentially in patients scheduled for first-line treatment. Therefore, we propose that clinical studies testing the efficacy of neratinib are warranted selectively in breast cancer patients whose tumors carry both amplification and mutation of ERBB2/HER2.

High-Throughput Functional Evaluation of Variants of Unknown Significance in ERBB2

Purpose: The advent of next-generation sequencing technologies has enabled the identification of several activating mutations of Erb-B2 receptor tyrosine kinase 2 (ERBB2) among various cancers. However, the significance of infrequent mutations has not been fully investigated. Herein, we comprehensively assessed the functional significance of the ERBB2 mutations in a high-throughput manner.Experimental Design: We evaluated the transforming activities and drug sensitivities of 55 nonsynonymous ERBB2 mutations using the mixed-all-nominated-in-one (MANO) method.Results: G776V, G778_S779insG, and L841V were newly revealed to be activating mutations. Although afatinib, neratinib, and osimertinib were shown to be effective against most of the ERBB2 mutations, only osimertinib demonstrated good efficacy against L755P and L755S mutations, the most common mutations in breast cancer. In contrast, afatinib and neratinib were predicted to be more effective than other inhibitors for the A775_776insYVMA mutation, the most frequent ERBB2 mutation in lung cancer. We surveyed the prevalence of concurrent ERBB2 mutation with gene amplification and found that approximately 30% of ERBB2-amplified urothelial carcinomas simultaneously carried ERBB2 mutations, altering their sensitivity to trastuzumab, an mAb against ERBB2. Furthermore, the MANO method was applied to evaluate the functional significance of 17 compound mutations within ERBB2 reported in the COSMIC database, revealing that compound mutations involving L755S were sensitive to osimertinib but insensitive to afatinib and neratinib.Conclusions: Several ERBB2 mutations showed varying sensitivities to ERBB2-targeted inhibitors. Our comprehensive assessment of ERBB2 mutations offers a fundamental database to help customize therapy for ERBB2-driven cancers.We identified several ERBB2 mutations as activating mutations related to tumorigenesis. In addition, our comprehensive evaluation revealed that several ERBB2 mutations showed varying sensitivities to ERBB2-targeted inhibitors, and thus, the functional significance of each variant should be interpreted precisely to design the best treatment for each patient. Clin Cancer Res; 24(20); 5112-22. ©2018 AACR.