Stemming resistance to HER-2 targeted therapy

A single centre experience in Turkey for comparison between core needle biopsy and surgical specimen evaluation results for HER2, SISH, estrogen receptors and progesterone receptors in breast cancer patients

Background

Breast carcinoma diagnosis can be made with core-needle biopsy (CNB), but there are controversies regarding the evaluation of hormone receptor (HR) status in needle biopsy specimens. When preoperative neoadjuvant therapy is required in breast cancer cases, the CNB specimen should be evaluated to decide on the treatment.

Objectives

In this study, we aimed to compare the estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and silver in situ hybridization (SISH) results of the CNB specimens and surgical specimens (SS) of our breast carcinoma cases.

Materials and Methods

This retrospective study included cases diagnosed with breast cancer in our center for approximately 1 year between 2017 and 2018. About 97 cases with both CNB specimens and SS were included in the study. Data such as the ER, PR, HER2, and SISH evaluation results in CNB and SS, age distribution and histopathological type, metastatic lymph nodes, lymphovascular invasion, tumor size, and grade of the tumor were recorded. The data were analyzed using SPSS 22.0 (Statistical Package for the Social Sciences, Armonk, NY, USA) software.

Results

All of the cases were female and 70.1% of them were aged over 45. About 27.8% of the cases were aged 31-45 years, and 2.1% were aged under 30. When evaluated according to the histopathological type of the tumor, 71.1% of cases were invasive ductal carcinoma (IDC), 8.2% were invasive lobular carcinoma (ILC), 6.2% were IDC + ILC, 11.3% were another carcinoma, and 3.1% were in situ carcinoma. 12.4% of the cases were Grade I, 43.3% were Grade II, and 20.6% were Grade III. 43.3% of our cases' tumor size were ≤2 cm and 56.7% >2 cm. 50 (51.5%) of these cases had no lymph node metastasis. It was found out that 36 (37.1%) of the cases had 1-4 metastatic lymph nodes and 11 (11.3%) of them had 5 and more metastatic lymph nodes. It was found out that 44 (45.4.%) of the cases had no lymphovascular invasion and 53 (54.6%) of them had a lymphovascular invasion. When HR statuses in CNB and SS were compared, ER was found to have a sensitivity of 96.1% and a specificity of 100%. PR was found to have a sensitivity of 94.2% and a specificity of 66.7%. HER2 was found to have a sensitivity of 100% and a specificity of 73.4%.

Conclusion

ER evaluation results are reliable in deciding on needle biopsy material. PR may show the heterogeneous distribution in HER2 tumor. Thus, if PR and HER2 results in needle biopsy material are negative, assessments should be repeated in SS.

Association Between Vascular Index Measured via Superb Microvascular Imaging and Molecular Subtype of Breast Cancer

Background

To determine whether vascular index (VI; defined as the ratio of Doppler signal pixels to pixels in the total lesion) measured via superb microvascular imaging in breast cancer correlates with immunohistochemically defined subtype and is able to predict molecular subtypes.

Methods

This prospective study involved 225 patients with 225 mass-type invasive breast cancers (mean size 2.6 ± 1.4 cm, range 0.4~5.9 cm) who underwent ultrasound and superb microvascular imaging (SMI) at Peking Union Medical College Hospital before breast surgery from December 2016 to June 2018. The correlations between primary tumor VI measured via SMI, clinicopathological findings, and molecular subtype were analyzed. The performance of VI for prediction of molecular subtypes in invasive breast cancer was investigated.

Results

The median VI of the 225 tumors was 7.3% (4.2%~11.8%) (range 0%~54.4%). Among the subtypes of the 225 tumors, 41 (18.2%) were luminal A, 91 (40.4%) were luminal B human epidermal growth factor receptor-2 (HER-2)-negative, 26 (11.6%) were luminal B HER-2-positive, 17 (7.6%) were HER-2-positive, and 50 (22.2%) were triple-negative, and the corresponding median VI values were 5.9% (2.6%~11.6%) (range 0%~47.1%), 7.3 (4.4%~10.5%) (range 0%~29.5%), 6.3% (3.9%~11.3%) (range 0.6%~22.2%), 8.2% (4.9%~15.6%) (range 0.9%~54.4%), and 9.2% (5.1%~15.3%) (range 0.7%~32.9%), respectively. Estrogen receptor (ER) negativity, higher tumor grade, and higher Ki-67 index (≥20%) were significantly associated with a higher VI value. Tumor size, ER status, and Ki-67 index were shown to independently influence VI. A cutoff value of 4.1% yielded 79.9% sensitivity and 41.5% specificity with an area under the receiver operating characteristic curve (AUC) of 0.58 for predicting that a tumor was of the luminal A subtype. A cutoff value of 16.4% yielded 30.0% sensitivity and 90.3% specificity with an AUC of 0.60 for predicting a triple-negative subtype.

Conclusions

VI, as a quantitative index obtained by SMI examination, could reflect histologic vascular changes in invasive breast cancer and was found to be higher in more biologically aggressive breast tumors. VI shows a certain degree of correlation with the molecular subtype of invasive breast cancer and plays a limited role in predicting the luminal A with high sensitivity and triple-negative subtype with high specificity.

Cyclin-Dependent Kinase 4 and 6 Inhibitors in Cell Cycle Dysregulation for Breast Cancer Treatment

In cell development, the cell cycle is crucial, and the cycle progression’s main controllers are endogenous CDK inhibitors, cyclin-dependent kinases (CDKs), and cyclins. In response to the mitogenic signal, cyclin D is produced and retinoblastoma protein (Rb) is phosphorylated due to activated CDK4/CDK6. This causes various proteins required in the cell cycle progression to be generated. In addition, complexes of CDK1-cyclin A/B, CDK2-cyclin E/A, and CDK4/CDK6-cyclin D are required in each phase of this progression. Cell cycle dysregulation has the ability to lead to cancer. Based on its role in the cell cycle, CDK has become a natural target of anticancer therapy. Therefore, understanding the CDK structures and the complex formed with the drug, helps to foster the development of CDK inhibitors. This development starts from non-selective CDK inhibitors to selective CDK4/CDK6 inhibitors, and these have been applied in clinical cancer treatment. However, these inhibitors currently require further development for various hematologic malignancies and solid tumors, based on the results demonstrated. In drug development, the main strategy is primarily to prevent and asphyxiate drug resistance, thus a determination of specific biomarkers is required to increase the therapy’s effectiveness as well as patient selection suitability in order to avoid therapy failure. This review is expected to serve as a reference for early and advanced-stage researchers in designing new molecules or repurposing existing molecules as CDK4/CDK6 inhibitors to treat breast cancer.

Predictive Value of CD44 for Prognosis in Patients with Breast Cancer

Background:

Breast Cancer (BC), is one of the most common malignancies around the world. CD44 expression correlates with cell proliferation, infiltration, angiogenesis, metastasis and prognosis in breast cancer but the exact mechanism of CD44 function is still not clear. The present study evaluates the expression of CD44 in primary HER2-positive breast cancer. The results can be used to determine the disease-free and overall survival of patients with breast cancer.

Methods:

We studied specimens from 100 patients with HER2-positive invasive breast cancer between March 2011 and June 2019. Immunohistochemical staining for CD44 was performed in all the specimens. Their CD44 association with clinicopathologic parameters and prognosis was evaluated.

Results:

The high CD44 was expression in 68(68%) of the patients and Low expression in 32(32%). CD44 expression was significantly associated with stage (p=0.007). There were no significant associations between the DFS, OS and other clinicopathologic parameters except for the stage, respectively (HR= 3.67, 95% CI =1.16-11.56, P = 0.03) (HR= 0.8.56, 95% CI =2.22-32.90, P = 0.002).20% of patients had died by the end of the follow-up. There were no significant association between DFS, OS and CD44 expression, respectively. (Log-rank p=0.13). (Log-rank p=0.10).

Conclusion:

The results from this study suggest that CD44 is clinically associated with stage of breast cancers. From the survival analysis, there was no statistical difference in overall survival and disease free survival with respect to CD44 expression. Further studies larger sample sizes are recommended for further investigation.

Salinomycin Treatment Specifically Inhibits Cell Proliferation of Cancer Stem Cells Revealed by Longitudinal Single Cell Tracking in Combination with Fluorescence Microscopy

A cell line derived from a tumor is a heterogeneous mixture of phenotypically different cells. Such cancer cell lines are used extensively in the search for new anticancer drugs and for investigating their mechanisms of action. Most studies today are population-based, implying that small subpopulations of cells, reacting differently to the potential drug go undetected. This is a problem specifically related to the most aggressive single cancer cells in a tumor as they appear to be insensitive to the drugs used today. These cells are not detected in population-based studies when developing new anticancer drugs. Thus, to get a deeper understanding of how all individual cancer cells react to chemotherapeutic drugs, longitudinal tracking of individual cells is needed. Here we have used digital holography for long time imaging and longitudinal tracking of individual JIMT-1 breast cancer cells. To gain further knowledge about the tracked cells, we combined digital holography with fluorescence microscopy. We grouped the JIMT-1 cells into different subpopulations based on expression of CD24 and E-cadherin and analyzed cell proliferation and cell migration for 72 h. We investigated how the cancer stem cell (CSC) targeting drug salinomycin affected the different subpopulations. By uniquely combining digital holography with fluorescence microscopy we show that salinomycin specifically targeted the CD24− subpopulation, i.e., the CSCs, by inhibiting cell proliferation, which was evident already after 24 h of drug treatment. We further found that after salinomycin treatment, the surviving cells were more epithelial-like due to the selection of the CD24+ cells.

Molecular Classification of Breast Cancer

Cancer classification aims to provide an accurate diagnosis of the disease and prediction of tumor behavior to facilitate oncologic decision making. Traditional breast cancer classification, mainly based on clinicopathologic features and assessment of routine biomarkers, may not capture the varied clinical courses of individual breast cancers. The underlying biology in cancer development and progression is complicated. Recent findings from high-throughput technologies added important information with regard to the underlying genetic alterations and the biological events in breast cancer. The information provides insights into new treatment strategies and patient stratifications that impact on the management of breast cancer patients. This review provides an overview of recent data on high throughput analysis of breast cancers, and it analyzes the relationship of these findings with traditional breast cancer classification and their clinical potentials.

The antigenic link between thyroid autoimmunity and breast cancer

The association between breast cancer and benign thyroid disorders, in particular thyroid autoimmunity, has been debated for decades. Autoantibodies to thyroid peroxidase, the hallmark of thyroid autoimmunity, have a higher prevalence among patients with breast cancer compared with the general population. Furthermore a correlation between their positivity and a better prognosis of breast cancer was found in several independent small-scale studies, even if such observation was not confirmed in a subsequent retrospective study conducted on the largest patient cohort to date. The thyroid and mammary glands present several biological similarities, therefore the hypothesis of an immune response to shared thyroid/breast antigens could in part explain the association between thyroid autoimmunity and breast cancer. The sodium iodide symporter is expressed in both glands, however it seems unlikely to be the key common antigen, considering that autoantibodies targeting it are rare. Instead thyroid peroxidase, one of the major thyroid autoantigens, is also expressed in breast tissue and therefore represents the main antigenic link between thyroid autoimmunity and breast cancer. Furthermore lactoperoxidase, an enzyme of the same family that shares structural similarities with thyroid peroxidase, is expressed in neoplastic breast cells and is responsible for the cross-reactivity with some autoantibodies to thyroid peroxidase. Novel strategies for the diagnosis and treatment of breast cancer might take advantage of the antigenic link between thyroid and breast tissues.

HER2 equivocal breast cancer that is positive by alternative probe HER2 FISH are classified as HER2 negative by Oncotype DX

In breast cancer, human epidermal growth factor receptor 2 (HER2) status is determined by immunohistochemistry (IHC) and/or in situ hybridization. Oncotype DX also reports HER2 status by an rt-PCR-based assay. Assay concordance between IHC and fluorescent in situ hybridization (FISH) (including alternative probe HER2 FISH) vs Oncotype DX HER2 rt-PCR has not been described in the post-2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2 Guideline revision setting. We performed a retrospective review of HER2 equivocal invasive breast carcinoma from 2014 to 2016 with the Oncotype DX HER2 result. Fifteen patients with HER2 equivocal invasive breast cancer had Oncotype DX performed. Of these, 13 underwent alternative probe HER2 FISH yielding 4 negative, 6 equivocal and 3 positive results. All 15 cases were classified as HER2 negative by Oncotype DX rt-PCR, including the three cases which were positive by alternative probe HER2 FISH, yielding a discordance rate for Oncotype DX rt-PCR HER2 of 20% (3/15). All three patients with HER2-positive breast cancer on the basis of alternative probe HER2 FISH received anti-HER2-targeted therapy. Treatment decisions based on HER2 status should utilize the IHC/FISH result as Oncotype DX results may incorrectly disqualify some patients from being eligible for anti-HER2 therapy based on the current 2013 ASCO/CAP HER2 Guidelines.

Cancer stem cell-driven efficacy of trastuzumab (Herceptin): towards a reclassification of clinically HER2-positive breast carcinomas

Clinically HER2+ (cHER2+) breast cancer (BC) can no longer be considered a single BC disease entity in terms of trastuzumab responsiveness. Here we propose a framework for predicting the response of cHER2+ to trastuzumab that integrates the molecular distinctions of intrinsic BC subtypes with recent knowledge on cancer stem cell (CSC) biology. First, we consider that two interchangeable populations of epithelial-like, aldehyde dehydrogenase (ALDH)-expressing and mesenchymal-like, CD44+CD24-/low CSCs can be found in significantly different proportions across all intrinsic BC subtypes. Second, we overlap all the intrinsic subtypes across cHER2+ BC to obtain a continuum of mixed phenotypes in which one extreme exhibits a high identity with ALDH+ CSCs and the other extreme exhibits a high preponderance of CD44+CD24-/low CSCs. The differential enrichment of trastuzumab-responsive ALDH+ CSCs versus trastuzumab-refractory CD44+CD24-/low CSCs can explain both the clinical behavior and the primary efficacy of trastuzumab in each molecular subtype of cHER2+ (i.e., HER2-enriched/cHER2+, luminal A/cHER2+, luminal B/cHER2+, basal/cHER2+, and claudin-low/cHER2+). The intrinsic plasticity determining the epigenetic ability of cHER2+ tumors to switch between epithelial and mesenchymal CSC states will vary across the continuum of mixed phenotypes, thus dictating their intratumoral heterogeneity and, hence, their evolutionary response to trastuzumab. Because CD44+CD24-/low mesenchymal-like CSCs distinctively possess a highly endocytic activity, the otherwise irrelevant HER2 can open the door to a type of "Trojan horse" approach by employing antibody-drug conjugates such as T-DM1, which will allow a rapid and CSC-targeted delivery of cytotoxic drugs to therapeutically manage trastuzumab-unresponsive basal/cHER2+ BC. Contrary to the current dichotomous model used clinically, our model proposes that a reclassification of cHER2+ tumors based on the spectrum of molecular BC subtypes might inform on their CSC-determined sensitivity to trastuzumab, thus providing a better delineation of the predictive value of cHER2+ in BC by incorporating CSCs-driven intra-tumor heterogeneity into clinical decisions.

Expression of breast cancer stem cell markers as predictors of prognosis and response to trastuzumab in HER2-positive breast cancer

Background:

Breast cancer stem cells (BCSCs) have been suggested to have clinical implications for cancer therapeutics because of their proposed role in chemoresistance. The aim of this study was to investigate the impact of BCSC marker expression on clinical outcome and trastuzumab response in human epidermal growth factor receptor 2 (HER2)-positive breast cancer.

Methods:

We analysed the expression of BCSC markers, CD44+/CD24− and aldehyde dehydrogenase 1 (ALDH1), and clinical outcomes in three sets of breast cancer cases: Set 1, 242 HER2-positive primary breast cancers treated by various modalities; Set 2, 447 HER2-positive primary breast cancers treated with surgery and chemotherapy plus adjuvant trastuzumab; Set 3, 112 metastatic HER2-positive breast cancers treated with trastuzumab.

Results:

Expression of CD44+/CD24− and ALDH1 was detected in 30.7% and 10.0%, respectively, of the Set 1 cases, and was associated with hormone receptor negativity. In survival analyses, expression of CD44+/CD24−, but not ALDH1, was found to be an independent prognostic factor for poor disease-free and overall survival in whole patients and also in the subgroup not receiving adjuvant trastuzumab. In Set 2 cases treated with adjuvant trastuzumab, CD44+/CD24− expression was an independent prognostic factor for poor disease-free survival, but not for overall survival; expression of ALDH1 had no impact on disease-free or overall survival. In metastatic disease treated with trastuzumab (Set 3 cases), CD44+/CD24− and ALDH1 expression had no effect on trastuzumab response or survival.

Conclusions:

These results suggest that the CD44+/CD24− phenotype can be used as a prognostic factor for clinical outcome and a predictive factor of trastuzumab response in patients with HER2-positive primary breast cancer.

Anthocyanins inhibit trastuzumab-resistant breast cancer in vitro and in vivo

Trastuzumab (Herceptin®) is a recombinant humanized monoclonal antibody that is targeted against the human epidermal growth factor receptor 2 (HER2) tyrosine kinase receptor. Trastuzumab has been successfully used to treat patients with HER2-positive breast cancer, which accounts for ~25% of invasive breast cancer. However, the majority of patients who initially respond to trastuzumab demonstrate disease progression within 1 year of treatment. Therefore, identifying alternative drugs that overcome trastuzumab resistance and target HER2 may increase the magnitude and duration of response. Through a high‑throughput screening approach, we previously identified numerous anthocyanins that exert activity in HER2‑positive human breast cancer cell lines. The present study aimed to evaluate the anti‑tumor properties of anthocyanins against parental HER2‑positive cells and derivative trastuzumab‑resistant cells in vitro and in vivo. Cell proliferation, western blotting, Annexin V staining, migration and invasion assays were used to determine the effects of anthocyanins in vitro. Cyanidin-3-glucoside and peonidin-3-glucoside were able to inhibit phosphorylation of HER2, induce apoptosis, suppress migration and invasion, and inhibit tumor cell growth. Coupled with the fact that anthocyanins have been used for decades as supplements for the treatment of various types of cancer in Asia, the present study may have established a framework for the development and testing of anthocyanins as a novel treatment paradigm used to overcome classical trastuzumab-resistance and to improve the outcome of this disease.

A class of genes in the HER2 regulon that is poised for transcription in breast cancer cell lines and expressed in human breast tumors

HER2-positive breast cancer accounts for 25% of all cases and has a poor prognosis. Although progress has been made in understanding signal transduction, little is known of how HER2 achieves gene regulation. We performed whole genome expression analysis on a HER2⁺ and HER2⁻ breast cancer cell lines and compared these results to expression in 812 primary tumors stratified by their HER2 expression level. Chip-on-chip with anti-RNA polymerase II was compared among breast cancer cell lines to identify genes that are potentially activated by HER2. The expression levels of these HER2-dependent POL II binding genes were determined for the 812 HER2+/− breast cancer tissues. Genes differentially expressed between HER2+/− cell lines were generally regulated in the same direction as in breast cancer tissues. We identified genes that had POLII binding in HER2⁺ cell lines, but without significant gene expression. Of 737 such genes “poised” for expression in cell lines, 113 genes were significantly differentially expressed in breast tumors in a HER2-dependent manner. Pathway analysis of these 113 genes revealed that a large group of genes were associated with stem cell and progenitor cell control as indicated by networks centered on NANOG, SOX2, OCT3/4. HER2 directs POL II binding to a large number of genes in breast cancer cells. A “poised” class of genes in HER2⁺ cell lines with POLII binding and low RNA expression but is differentially expressed in primary tumors, strongly suggests a role of the microenvironment and further suggests a role for stem cells proliferation in HER2-regulated breast cancer tissue.

Role of ErbB Receptors in Cancer Cell Migration and Invasion

Growth factors mediate their diverse biologic responses (regulation of cellular proliferation, differentiation, migration and survival) by binding to and activating cell-surface receptors with intrinsic protein kinase activity named receptor tyrosine kinases (RTKs). About 60 RTKs have been identified and can be classified into more than 16 different receptor families. Their activity is normally tightly controlled and regulated. Overexpression of RTK proteins or functional alterations caused by mutations in the corresponding genes or abnormal stimulation by autocrine growth factor loops contribute to constitutive RTK signaling, resulting in alterations in the physiological activities of cells. The ErbB receptor family of RTKs comprises four distinct receptors: the EGFR (also known as ErbB1/HER1), ErbB2 (neu, HER2), ErbB3 (HER3) and ErbB4 (HER4). ErbB family members are often overexpressed, amplified, or mutated in many forms of cancer, making them important therapeutic targets. EGFR has been found to be amplified in gliomas and non-small-cell lung carcinoma while ErbB2 amplifications are seen in breast, ovarian, bladder, non-small-cell lung carcinoma, as well as several other tumor types. Several data have shown that ErbB receptor family and its downstream pathway regulate epithelial-mesenchymal transition, migration, and tumor invasion by modulating extracellular matrix (ECM) components. Recent findings indicate that ECM components such as matrikines bind specifically to EGF receptor and promote cell invasion. In this review, we will present an in-depth overview of the structure, mechanisms, cell signaling, and functions of ErbB family receptors in cell adhesion and migration. Furthermore, we will describe in a last part the new strategies developed in anti-cancer therapy to inhibit ErbB family receptor activation.

Artemin, a member of the glial cell line-derived neurotrophic factor family of ligands, is HER2-regulated and mediates acquired trastuzumab resistance by promoting cancer stem cell-like behavior in mammary carcinoma cells

Previous studies have demonstrated that Artemin (ARTN) functions as a cancer stem cell (CSC) and metastatic factor in mammary carcinoma. Herein, we report that ARTN mediates acquired resistance to trastuzumab in HER2-positive mammary carcinoma cells. Ligands that increase HER2 activity increased ARTN expression in HER2-positive mammary carcinoma cells, whereas trastuzumab inhibited ARTN expression. Forced expression of ARTN decreased the sensitivity of HER2-positive mammary carcinoma cells to trastuzumab both in vitro and in vivo. Conversely, siRNA-mediated depletion of ARTN enhanced trastuzumab efficacy. Cells with acquired resistance to trastuzumab exhibited increased ARTN expression, the depletion of which restored trastuzumab sensitivity. Trastuzumab resistance produced an increased CSC population concomitant with enhanced mammospheric growth. ARTN mediated the enhancement of the CSC population by increased BCL-2 expression, and the CSC population in trastuzumab-resistant cells was abrogated upon inhibition of BCL-2. Hence, we conclude that ARTN is one mediator of acquired resistance to trastuzumab in HER2-positive mammary carcinoma cells.

The classification of invasive carcinoma of the breast

The classification of invasive breast carcinoma assists diagnosis, allows for comparison of different patient groups in clinical trials and facilitates epidemiological analysis. For the individual patient, accurate tumor classification informs clinical decision-making with emphasis on assessment of prognosis and treatment formulation. Tumor grade is an independent prognostic indicator and is calculated by assessing specific tumor characteristics microscopically. The Tumor Node Metastasis staging system, produced by the American Joint Committee on Cancer Union for International Cancer Control, combines information about the primary tumor size, the status of the regional lymph nodes and the presence or absence of distant metastases at diagnosis to classify disease. In recent years, the use of gene expression profiling technology has led to the development of the molecular classification of breast cancer and has highlighted the importance of hormone receptor and HER2 oncogenic pathways, with particular reference to targeted chemotherapy. Tumor typing involves the identification of 'no special type' carcinoma with variable clinical, histological and molecular characteristics and 'special type' carcinomas that are usually associated with a particular set of prognostic and predictive indices. Some special type carcinomas have unique biological features that influence diagnostic investigation and clinical management.

PIK3CA gene amplification and PI3K p110α protein expression in breast carcinoma

A family of PI3Ks is the lipid kinases, which enhance intracellular pools of phosphatidyl inositol 3,4,5-tri-phosphate (PIP3) through phosphorylating its precursor. Amplifications and deletions of genes, as well as somatic missense of the PIK3CA gene have been described in many human cancer varieties, including of the brain, colon, liver, lung and stomach. Immunohistochemistry and Real-time quantitative PCR tests were used to determine the PIK3CA gene amplification (gene copy number) and to detect protein expression, respectively. The results obtained were analysed and the ratio of PIK3CA to β-actin gene copy number was calculated. Positive gene amplification of PIK3CA was appointed as a copy number of ≥4. Also, PI3K p110α protein expression was scored from 0 to 3+ and the scores of 2+ and 3+ were considered as positive for PI3K p110α protein expression. We studied 50 breast carcinoma samples for PI3K p110α protein expression and PIK3CA gene copy numbers. In general, 36 out of 50 (72%) breast carcinoma samples showed a significant increase in PIK3CA gene amplification. 12 out of 50 (24%) showed positive staining, and 38 out of 50 (76%) showed negative staining for PI3K p110α expression. We have identified no significant relationship between PIK3CA amplification, race (p= 0.630) and histological type (p=0. 731) in breast carcinoma, but correlation of PIK3CA amplification and age showed a significant relationship (p=0. 003) between them. No significant relationship has been identified in correlation of PI3K p110α protein expression compared to age (p=0. 284), race (p=0. 546) and histological type (p=0. 285). Amplification of PIK3CA was frequent in breast carcinoma and occurs in stages of breast carcinoma. Our result shows that there is a relationship between gene amplification and age in breast carcinoma. We suggest that PIK3CA is significant in breast tumorigenesis serve as a prevalent mechanism contributes to the oncogenic activation pathway of PIK3CA in breast cancer.

PPARγ maintains ERBB2-positive breast cancer stem cells

Overexpression of the adverse prognostic marker ERBB2 occurs in 30% of breast cancers and is associated with aggressive disease and poor outcomes. Our recent findings have shown that NR1D1 and the peroxisome proliferator-activated receptor-γ (PPARγ)-binding protein (PBP) act through a common pathway in upregulating several genes in the de novo fatty acid synthesis network, which is highly active in ERBB2-positive breast cancer cells. NR1D1 and PBP are functionally related to PPARγ, a well-established positive regulator of adipogenesis and lipid storage. Here, we report that inhibition of the PPARγ pathway reduces the aldehyde dehydrogenase (ALDH)-positive population in ERBB2-positive breast cancer cells. Results from in vitro tumorsphere formation assays demonstrate that the PPARγ antagonists GW9662 and T0070907 decrease tumorsphere formation in ERBB2-positive cells, but not other breast cells. We show that the mechanism by which GW9662 treatment causes a reduction in ALDH-positive population cells is partially due to ROS, as it can be rescued by treatment with N-acetyl-cysteine. Furthermore, global gene expression analyses show that GW9662 treatment suppresses the expression of several lipogenic genes, including ACLY, MIG12, FASN and NR1D1, and the stem-cell related genes KLF4 and ALDH in BT474 cells. Antagonist treatment also decreases the level of acetylation in histone 3 and histone 4 in BT474 cells, compared with MCF7 cells. In vivo, GW9662 pre-treatment inhibits the tumor-seeding ability of BT474 cells. Together, these results show that the PPARγ pathway is critical for the cancer stem cell properties of ERBB2-positive breast cancer cells.

Targeted therapies of metastatic breast cancer: relationships with cancer stem cells

In the last years, many targeted agents have been developed for metastatic breast cancer (MBC) treatment and are being tested in clinical trials. In spite of this, apart from epidermal growth factor receptor 2 (HER2) positive subset, no significant increase in the median overall survival (OS) has been reported. Similarly to conventional chemo- and radiotherapy, the cancer stem cell theory has been evoked to explain the frustrating results often obtained with this emerging category of drugs. This review examines the results in MBC of the approved targeted therapies or those currently under evaluation in experimental studies or in clinical trials, in the light of their relationships with breast CSCs and of the efforts to circumvent the development of resistance. In the next, there is the principal need to investigate if the effects on CSCs may be used to overcome cancer resistance and it will be opportune to consider whether molecular targeted therapies should be used alone or combined with conventional therapy, or with a different target drug specific for CSCs.

HER2-specific T lymphocytes kill both trastuzumab-resistant and trastuzumab-sensitive breast cell lines in vitro

OBJECTIVE

Although the development of trastuzumab has improved the outlook for women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, the resistance to anti-HER2 therapy is a growing clinical dilemma. We aim to determine whether HER2-specific T cells generated from dendritic cells (DCs) modified with HER2 gene could effectively kill the HER2-positive breast cancer cells, especially the trastuzumab-resistant cells.

METHODS

The peripheral blood mononuclear cells (PBMCs) from healthy donors, whose HLA haplotypes were compatible with the tumor cell lines, were transfected with reconstructive human adeno-association virus (rhAAV/HER2) to obtain the specific killing activities of T cells, and were evaluated by lactate dehydrogenase (LDH) releasing assay.

RESULTS

Trastuzumab produced a significant inhibiting effect on SK-BR-3, the IC50 was 100ng/ml. MDA-MB-453 was resistant to trastuzumab even at a concentration of 10,000 ng/ml in vitro. HER2-specific T lymphocytes killed effectively SK-BR-3 [(69.86±13.41)%] and MDA-MB-453 [(78.36±10.68)%] at 40:1 (effector:target ratio, E:T), but had no significant cytotoxicity against HER2-negative breast cancer cell lines MDA-MB-231 or MCF-7 (less than 10%).

CONCLUSION

The study showed that HER2-specific T lymphocytes generated from DCs modified by rhAAV/HER2 could kill HER2-positive breast cancer cell lines in a HER2-dependent manner, and result in significantly high inhibition rates on the intrinsic trastuzumab-resistant cell line MDA-MB-453 and the tastuzumab-sensitive cell line SK-BR-3. These results imply that this immunotherapy might be a potential treatment to HER2-positive breast cancer.

Salinomycin as a drug for targeting human cancer stem cells

Cancer stem cells (CSCs) represent a subpopulation of tumor cells that possess self-renewal and tumor initiation capacity and the ability to give rise to the heterogenous lineages of malignant cells that comprise a tumor. CSCs possess multiple intrinsic mechanisms of resistance to chemotherapeutic drugs, novel tumor-targeted drugs, and radiation therapy, allowing them to survive standard cancer therapies and to initiate tumor recurrence and metastasis. Various molecular complexes and pathways that confer resistance and survival of CSCs, including expression of ATP-binding cassette (ABC) drug transporters, activation of the Wnt/β-catenin, Hedgehog, Notch and PI3K/Akt/mTOR signaling pathways, and acquisition of epithelial-mesenchymal transition (EMT), have been identified recently. Salinomycin, a polyether ionophore antibiotic isolated from Streptomyces albus, has been shown to kill CSCs in different types of human cancers, most likely by interfering with ABC drug transporters, the Wnt/β-catenin signaling pathway, and other CSC pathways. Promising results from preclinical trials in human xenograft mice and a few clinical pilote studies reveal that salinomycin is able to effectively eliminate CSCs and to induce partial clinical regression of heavily pretreated and therapy-resistant cancers. The ability of salinomycin to kill both CSCs and therapy-resistant cancer cells may define the compound as a novel and an effective anticancer drug.

Breast cancer stem cells: new therapeutic approaches

SUMMARY Breast cancer stem cells are defined as a small subset of cells within a cancer that constitutes a reservoir of self-sustaining cells; they are low-dividing, have a reduced ability to undergo apoptosis and a higher ability of DNA repair, making them more resistant to conventional radiation and chemotherapy. The recent better understanding of the mechanisms of resistance to therapy related to stem cells has opened new scenarios and perspectives for therapeutic approaches. Some drugs active against breast cancer stem cells have been used in cancer therapy for years, other approaches are currently under clinical trials and many drugs are still in a preclinical phase. Only controlled clinical trials will answer the question whether or not these new therapeutical approaches alone or combined with the ongoing treatments significantly improve the outcome of breast cancer patients.

Metformin-induced preferential killing of breast cancer initiating CD44+CD24-/low cells is sufficient to overcome primary resistance to trastuzumab in HER2+ human breast cancer xenografts

Trastuzumab-refractory breast cancer stem cells (CSCs) could also explain the high rate of primary resistance to single-agent trastuzumab in HER2 gene-amplified breast cancer patients. The identification of agents with strong selective toxicity for trastuzumab-resistant breast CSCs may have tremendous relevance for how HER2+ breast cancer patients should be treated. Using the human breast cancer cell line JIMT-1, which was established from the pleural metastasis of a patient who was clinically resistant to trastuzumab ab initio, we examined whether preferential killing of the putative CD44+CD24-/low breast CSC population might be sufficient to overcome primary resistance to trastuzumab in vivo. Because recent studies have shown that the anti-diabetic biguanide metformin can exert antitumor effects by targeted killing of CSC-like cells, we explored whether metformin's ability to preferentially kill breast cancer initiating CD44+CD24-/low cells may have the potential to sensitize JIMT-1 xenograft mouse models to trastuzumab. Upon isolation for breast cancer initiating CD44+CD24-/low cells by employing magnetic activated cell sorting, we observed the kinetics of metformin-induced killing drastically varied among CSC and non-CSC subpopulations. Metformin's cell killing effect increased dramatically by more than 10-fold in CD44+CD24-/low breast CSC cells compared to non-CD44+CD24-/low immunophenotypes. While seven-weeks treatment length with trastuzumab likewise failed to reduce tumor growth of JIMT-1 xenografts, systemic treatment with metformin as single agent resulted in a significant two-fold reduction in tumor volume. When trastuzumab was combined with concurrent metformin, tumor volume decreased sharply by more than four-fold. Given that metformin-induced preferential killing of breast cancer initiating CD44+CD24-/low subpopulations is sufficient to overcome in vivo primary resistance to trastuzumab, the incorporation of metformin into trastuzumab-based regimens may provide a valuable strategy for treatment of HER2+ breast cancer patients.

Epithelial-to-mesenchymal transition (EMT) confers primary resistance to trastuzumab (Herceptin)

The rate of inherent resistance to single-agent trastuzumab in HER2-overexpressing metastatic breast carcinomas is impressive at above 70%. Unfortunately, little is known regarding the distinctive genetic signatures that could predict trastuzumab refractoriness ab initio. The epithelial-to-mesenchymal transition (EMT) molecular features, HER2 expression status and primary responses to trastuzumab were explored in the public Lawrence Berkeley Laboratory (LBL) Breast Cancer Collection. Lentivirus-delivered small hairpin RNAs were employed to reduce specifically and stably the expression of EMT transcription factors in trastuzumab-refractory basal/HER2+ cells. Cell proliferation assays and pre-clinical nude mice xenograft-based studies were performed to assess the contribution of specific EMT transcription factors to inherent trastuzumab resistance. Primary sensitivity to trastuzumab was restricted to the SLUG/SNAIL2-negative subset of luminal/HER2+ cell lines, whereas all of the SLUG/SNAIL2-positive basal/HER2+ cell lines exhibited an inherent resistance to trastuzumab. The specific knockdown of SLUG/SNAIL2 suppressed the stem-related CD44+CD24(-/low) mesenchymal immunophenotype by transcriptionally upregulating the luminal epithelial marker CD24 in basal/HER2+ cells. Basal/HER2+ cells gained sensitivity to the growth-inhibitory effects of trastuzumab following SLUG/SNAIL2 gene depletion, which induced the expression of the mesenchymal-to-epithelial transition (MET) genes involved in promoting an epithelial phenotype. The isolation of CD44+CD24(-/low) mesenchymal cells by magnetic-activated cell sorting (MACS) confirmed their intrinsic unresponsiveness to trastuzumab. A reduction in tumor growth and dramatic gain in sensitivity to trastuzumab in vivo were confirmed when the SLUG/SNAIL2 knockdown basal/HER2+ cells were injected into nude mice. HER2 overexpression in a basal, rather than in a luminal molecular background, results in a basal/HER2+ breast cancer subtype that is intrinsically resistant to trastuzumab. EMT transcription factors might induce an enhanced phenotypic plasticity that would allow basal/HER2+ breast cancer cells to "enter" into and "exit" dynamically from trastuzumab-responsive stem cell-like states. The systematic determination of SLUG/SNAIL2 as a stem/CD44+CD24(-/low) cell-associated protein may improve the therapeutic management of HER2+ breast carcinomas.

Epithelial-mesenchymal transition and stem cell markers in patients with HER2-positive metastatic breast cancer

Currently, there is extensive information about circulating tumor cells (CTC) and their prognostic value; however, little is known about other characteristics of these cells. In this prospective study, we assessed the gene transcripts of epithelial-to-mesenchymal transition-inducing transcription factors (EMT-TF) and cancer stem cell (CSC) features in patients with HER2(+) metastatic breast cancer (MBC). Epithelial cells were enriched from peripheral blood mononuclear cells (PBMC) using antibody-coated anti-CD326 antibody (CD326(+)) magnetic beads, and the residual CD326(-) PBMCs were further depleted of leukocytes using anti-CD45 antibody-coated magnetic beads (CD326(-)CD45(-)). RNA was extracted from all cell fractions, reverse transcribed to cDNA, and subjected to quantitative reverse transcription PCR to detect EMT-TFs (TWIST1, SNAIL1, ZEB1, and TG2) as a measure of CTCs undergoing EMT (EMT-CTCs). In addition, PBMCs were analyzed using multiparameter flow cytometry for ALDH activity and CSCs that express CD24, CD44, and CD133. Twenty-eight patients were included in this study. At least one EMT-TF mRNA was elevated in the CTCs of 88.2% of patients and in the CD326(-)CD45(-) cell fraction of 60.7% of patients. The CD326(-)CD45(-) fraction of patients with elevated SNAIL1 and ZEB1 transcripts also had a higher percentage of ALDH(+)/CD133(+) cells in their blood than did patients with normal SNAIL1 and ZEB1 expression (P = 0.038). Our data indicate that patients with HER2(+) MBCs have EMT-CTCs. Moreover, an enrichment of CSCs was found in CD326(-)CD45(-) cells. Additional studies are needed to determine whether EMT-CTCs and CSCs have prognostic value in patients with HER2(+) MBCs treated with trastuzumab-based therapy.

A phase II study of afatinib (BIBW 2992), an irreversible ErbB family blocker, in patients with HER2-positive metastatic breast cancer progressing after trastuzumab

Afatinib is an oral, ErbB family blocker, which covalently binds and irreversibly blocks all kinase-competent ErbB family members. This phase II, open-label, single-arm study explored afatinib activity in human epidermal growth factor receptor 2 (HER2)-positive breast cancer patients progressing after trastuzumab treatment. Patients had stage IIIB/IV HER2-positive metastatic breast cancer, with progression following trastuzumab or trastuzumab intolerance and an Eastern Cooperative Oncology Group (ECOG) performance status of 0–2. Patients received 50 mg afatinib once-daily until disease progression. Primary endpoint was objective response rate (Response Evaluation Criteria in Solid Tumors 1.0), with tumor assessments every 8 weeks. Forty-one patients were treated. Patients had received a median of three prior chemotherapy lines (range, 0–15) and 68.3% had received trastuzumab for >1 year. Four patients (10% of 41 treated; 11% of evaluable patients) had partial response. Fifteen patients (37% of 41) had stable disease as best response and 19 (46% of 41) achieved clinical benefit. Median progression-free survival was 15.1 weeks (95% confidence interval [CI]: 8.1–16.7); median overall survival was 61.0 weeks (95% CI: 56.7–not evaluable). Most frequent common terminology criteria for adverse events grade 3 treatment-related adverse events were diarrhea (24.4%) and rash (9.8%). Afatinib monotherapy was associated with promising clinical activity in extensively pretreated HER2-positive breast cancer patients who had progressed following trastuzumab treatment.

Basal/HER2 breast carcinomas: integrating molecular taxonomy with cancer stem cell dynamics to predict primary resistance to trastuzumab (Herceptin)

High rates of inherent primary resistance to the humanized monoclonal antibody trastuzumab (Herceptin) are frequent among HER2 gene-amplified breast carcinomas in both metastatic and adjuvant settings. The clinical efficacy of trastuzumab is highly correlated with its ability to specifically and efficiently target HER2-driven populations of breast cancer stem cells (CSCs). Intriguingly, many of the possible mechanisms by which cancer cells escape trastuzumab involve many of the same biomarkers that have been implicated in the biology of CS-like tumor-initiating cells. In the traditional, one-way hierarchy of CSCs in which all cancer cells descend from special self-renewing CSCs, HER2-positive CSCs can occur solely by self-renewal. Therefore, by targeting CSC self-renewal and resistance, trastuzumab is expected to induce tumor shrinkage and further reduce breast cancer recurrence rates when used alongside traditional therapies. In a new, alternate model, more differentiated non-stem cancer cells can revert to trastuzumab-refractory, CS-like cells via the activation of intrinsic or microenvironmental paths-to-stemness, such as the epithelial-to-mesenchymal transition (EMT). Alternatively, stochastic transitions of trastuzumab-responsive CSCs might also give rise to non-CSC cellular states that lack major attributes of CSCs and, therefore, can remain "hidden" from trastuzumab activity. Here, we hypothesize that a better understanding of the CSC/non-CSC social structure within HER2-overexpressing breast carcinomas is critical for trastuzumab-based treatment decisions in the clinic. First, we decipher the biological significance of CSC features and the EMT on the molecular effects and efficacy of trastuzumab in HER2-positive breast cancer cells. Second, we reinterpret the genetic heterogeneity that differentiates trastuzumab-responders from non-responders in terms of CSC cellular states. Finally, we propose that novel predictive approaches aimed at better forecasting early tumor responses to trastuzumab should identify biological determinants that causally underlie the intrinsic flexibility of HER2-positive CSCs to "enter" into or "exit" from trastuzumab-sensitive states. An accurate integration of CSC cellular states and EMT-related biomarkers with the currently available breast cancer molecular taxonomy may significantly improve our ability to make a priori decisions about whether patients belonging to HER2 subtypes differentially enriched with a "mesenchymal transition signature" (e.g., luminal/HER2 vs. basal/HER2) would distinctly benefit from trastuzumab-based therapy ab initio.

Stem cell property epithelial-to-mesenchymal transition is a core transcriptional network for predicting cetuximab (Erbitux™) efficacy in KRAS wild-type tumor cells

Beyond a well-recognized effect of KRAS mutations in determining de novo inefficacy of cetuximab (CTX) in metastatic colorectal cancer, we urgently need a biomarker signature for predicting CTX efficacy in KRAS wild-type (WT) tumors. CTX-adapted EGFR gene-amplified KRAS WT tumor cell populations were induced by stepwise-chronic exposure of A431 epidermoid cancer cells to CTX. Genome-wide analyses of 44K Agilent's whole human arrays were bioinformatically evaluated by Gene Set Enrichment Analysis (GSEA)-based screening of the KEGG pathway database. Molecular functioning of CTX was found to depend on: (i) The occurrence of a positive feedback loop on Epidermal Growth Factor Receptor (EGFR) activation driven by genes coding for EGFR ligands (e.g., amphiregulin); (ii) the lack of a negative feedback on mitogen-activated protein kinase (MAPK) activation regulated by dual-specificity phosphatases (e.g., DUSP6) and; (iii) the transcriptional status of gene pathways controlling the epithelial-to-mesenchymal transition (EMT) and its reversal (MET) program (actin cytoskeleton and cell-cell communication-e.g., keratins-focal adhesion signaling-e.g., integrins-and EMT-inducing cytokines - e.g., transforming growth factor-β). Quantitative real-time PCR, high-content immunostaining, and flow-cytometry analyses confirmed that CTX efficacy depends on its ability to promote: (i) Stronger cell-cell contacts by up-regulating the expression of the epithelial markers E-cadherin and occludin; (ii) down-regulation of the epithelial transcriptional repressors Zeb, Snail, and Slug accompanied by restoration of cortical F-actin; and (iii) complete prevention of the CD44(pos)/CD24(neg/low) mesenchymal immunophenotype. The impact of EGFR ligands/MAPK phosphatases gene transcripts in predicting CTX efficacy in KRAS WT tumors may be tightly linked with the ability of CTX to concurrently reverse the EMT status, a pivotal property of migrating cancer stem cells.

Approaches and limitations of phosphatidylinositol-3-kinase pathway activation status as a predictive biomarker in the clinical development of targeted therapy

The central role played by the class I(A) phosphatidylinositol-3-kinase (PI3K) signaling node in human cancer is highlighted in the multiple mechanisms by which these signals become dysregulated. Many studies suggest that constitutive PI3K activation in human cancer contributes to drug resistance, including targeted agents and standard cytotoxic therapy. The combination of activation mechanisms and the multiple downstream cascades that emanate from the PI3K node contributes to the difficulty in measuring PI3K activation as a biomarker. Although many agents suppress the pathway in models, the challenge remains to translate this biology into a patient selection strategy (i.e., identify patients with "PI3K activated" tumors) and subsequently link this biomarker definition to drug responses in patients. The various genetic and epigenetic lesions resulting in pathway activation necessitate combined approaches using genetic, genomic, and protein biomarkers to accurately characterize "PI3K activated" tumors. Such a combined approach to pathway status can be assessed using a statistical stratification of patients in a randomized trial into "pathway on" and "pathway off" subsets to compare the treatment effect in each arm. Instead of considering individual biomarkers for their predictive ability, this strategy proposes the use of a collection of biomarkers to identify a specific "pathway on" patient population predicted to have clinical benefit from a pathway inhibitor. Here, we review the current understanding of the mechanisms of PI3K activation in breast cancer and discuss a pathway-based approach using PI3K as a predictive biomarker in clinical development, which is currently in use in a global phase 3 setting.

The anti-diabetic drug metformin suppresses self-renewal and proliferation of trastuzumab-resistant tumor-initiating breast cancer stem cells

We here demonstrate that the anti-diabetic drug metformin interacts synergistically with the anti-HER2 monoclonal antibody trastuzumab (Tzb; Herceptin™) to eliminate stem/progenitor cell populations in HER2-gene-amplified breast carcinoma cells. When using the mammosphere culture technique, graded concentrations of single-agent metformin (range 50-1,000 μmol/l) were found to dose-dependently reduce the number of mammospheres formed by SKBR3 (a Tzb-naïve model), SKBR3 TzbR (a model of acquired auto-resistance to Tzb) and JIMT-1 (a model of refractoriness to Tzb and other HER2-targeted therapies ab initio) HER2-overexpressing breast cancer cells. Single-agent Tzb likewise reduced mammosphere-forming efficiency (MSFE) in Tzb-naïve SKBR3 cells, but it failed to significantly decrease MSFE in Tzb-resistant SKBR3 TzbR and JIMT-1 cells. Of note, CD44-overexpressing Tzb-refractory SKBR3 TzbR and JIMT-1 cells retained an exquisite sensitivity to single-agent metformin. Concurrent combination of metformin with Tzb synergistically reduced MSFE as well as the size of mammospheres in Tzb-refractory SKBR3 TzbR and JIMT-1 cells. Flow cytometry analyses confirmed that metformin and Tzb functioned synergistically to down-regulate the percentage of Tzb-refractory JIMT-1 cells displaying the CD44(pos)/CD24(neg/low) stem/progenitor immunophenotype. Given that MSFE and mammosphere size are indicators of stem self-renewal and progenitor cell proliferation, respectively, our current findings reveal for the first time that: (a) Tzb refractoriness in HER2 overexpressors can be explained in terms of Tzb-resistant/CD44-overexpressing/tumor-initiating stem cells; (b) metformin synergistically interacts with Tzb to suppress self-renewal and proliferation of cancer stem/progenitor cells in HER2-positive carcinomas.

Issues and updates: evaluating estrogen receptor-alpha, progesterone receptor, and HER2 in breast cancer

There are currently three prognostic/predictive biomarkers used in routine clinical management of patients with breast cancer, and their assessment is mandatory. They include estrogen receptor-alpha (ERalpha), progesterone receptor (PgR), and the HER2 oncogene/oncoprotein. This paper briefly reviews the assessment of ERalpha, PgR, and HER2 in breast cancer, emphasizing recent progress and persistent controversies.

HER2 targeting as a two-sided strategy for breast cancer diagnosis and treatment: Outlook and recent implications in nanomedical approaches

At present, mammary carcinoma is the second most common type of malignant tumor in adult women after lung cancer, as more than one million women are diagnosed with breast cancer every year. Despite advances in diagnosis and treatment, which have resulted in a decrease in mortality in recent decades, breast cancer remains a major public health problem. One of the most significant unresolved clinical and scientific problems is the occurrence of resistance to clinical treatments and their toxicity (and how to predict, prevent and overcome them). However, the heterogeneity of human breast cancer in terms of genetic features, molecular profiles and clinical behavior represents a constraint obstructing the discovery of a solution to the disease. It is currently considered that the chances of success of therapy may increase if the tumor cells are selectively removed before they can evolve to their mature stages up to metastases production. Therefore, novel and more sensitive diagnostic tools are being developed, with the aim of improving the early and noninvasive detection of rising malignancies and the accuracy of tumor tissue localization. Meanwhile, there is an emerging use of targeted therapies in oncology, depending on the expression of specific proteins or genes present in tumor cells. Among the molecular targets considered for the treatment of breast cancer cells so far, we chose to focus on examples involving overexpression and/or gene amplification of "Human Epidermal growth factor Receptor 2" (HER2) protein. In current studies, various types of nanoparticles conjugated with the anti-HER2 monoclonal antibody, the so-called "trastuzumab", are investigated extensively due to promising results in biological and preclinical applications aimed at improving the treatment of breast cancer. In this paper, we present a critical review of the preparation and use of different kinds of trastuzumab-functionalized nanoparticles, with an emphasis on the therapeutic and diagnostic (theranostic) potential of this generation of hybrid nanoparticles, exploiting the multifaceted mechanisms of action of trastuzumab against malignant cells.