Phenotypic and molecular dissection of metaplastic breast cancer and the prognostic implications

Metaplastic carcinomas of the breast without evidence of epithelial differentiation: a diagnostic approach for management

AIMS

Although rare, malignant sarcomatoid breast tumours without evidence of epithelial differentiation comprise a diagnostic challenge with management implications. Earlier studies have generally considered these to be primary breast sarcomas; however, supporting evidence is lacking and management remains variable. This study aimed to provide an evidence-based approach to improve the consistency of diagnosis and management for such cases.

METHODS AND RESULTS

A large series (n = 140) of metaplastic breast carcinoma (MBC) diagnosed in Nottingham over 18 years was analysed. Only cases with available data on immunohistochemical expression of cytokeratins (CKs) were included. The prevalence and pattern of expression for various CKs were assessed and details of tumours negative for CKs were collected. A diagnostic approach based on our experience is provided. Forty-seven cases (34%) showed foci of conventional type invasive breast carcinoma or ductal carcinoma in situ (DCIS), while 93 cases (66%) were diagnosed as MBC based on morphology and/or CK expression. Ninety-seven cases (69%) were negative for one or more CKs, with 18 cases (13%) negative for five or more CKs. Eight cases (6%) lacked expression of all CKs tested. Further examination showed evidence of carcinomatous nature in five cases, and three were diagnosed as MBC following extensive diagnostic work-up and based on our experience.

CONCLUSION

This study suggests that MBC represents a spectrum of neoplasms, with some lacking CK expression. Sarcomatoid neoplasms of the breast lacking evidence of carcinomatous morphology and CK expression may represent an extreme end of differentiation that can be considered as carcinomas rather than sarcomas for management purposes (following extensive work-up).

A comprehensive overview of metaplastic breast cancer: clinical features and molecular aberrations

Metaplastic breast cancer (MpBC) is an exceedingly rare breast cancer variant that is therapeutically challenging and aggressive. MpBC is defined by the histological presence of at least two cellular types, typically epithelial and mesenchymal components. This variant harbors a triple-negative breast cancer (TNBC) phenotype, yet has a worse prognosis and decreased survival compared to TNBC. There are currently no standardized treatment guidelines specifically for MpBC. However, prior studies have found that MpBC typically has molecular alterations in epithelial-to-mesenchymal transition, amplification of epidermal growth factor receptor, PI3K/Akt signaling, nitric oxide signaling, Wnt/β-catenin signaling, altered immune response, and cell cycle dysregulation. Some of these molecular alterations have been studied as therapeutic targets, in both the preclinical and clinical setting. This current review discusses the histological organization and cellular origins of MpBC, molecular alterations, the role of radiation therapy, and current clinical trials for MpBC.

Evaluation of deacetylase inhibition in metaplastic breast carcinoma using multiple derivations of preclinical models of a new patient-derived tumor

Metaplastic breast carcinoma (MBC) is a clinically aggressive and rare subtype of breast cancer, with similar features to basal-like breast cancers. Due to rapid growth rates and characteristic heterogeneity, MBC is often unresponsive to standard chemotherapies; and novel targeted therapeutic discovery is urgently needed. Histone deacetylase inhibitors (DACi) suppress tumor growth and metastasis through regulation of the epithelial-to-mesenchymal transition axis in various cancers, including basal-like breast cancers. We utilized a new MBC patient-derived xenograft (PDX) to examine the effect of DACi therapy on MBC. Cell morphology, cell cycle-associated gene expressions, transwell migration, and metastasis were evaluated in patient-derived cells and tumors after treatment with romidepsin and panobinostat. Derivations of our PDX model, including cells, spheres, organoids, explants, and in vivo implanted tumors were treated. Finally, we tested the effects of combining DACi with approved chemotherapeutics on relative cell biomass. DACi significantly suppressed the total number of lung metastasis in vivo using our PDX model, suggesting a role for DACi in preventing circulating tumor cells from seeding distal tissue sites. These data were supported by our findings that DACi reduced cell migration, populations, and expression of mesenchymal-associated genes. While DACi treatment did affect cell cycle-regulating genes in vitro, tumor growth was not affected compared to controls. Importantly, gene expression results varied depending on the cellular or tumor system used, emphasizing the importance of using multiple derivations of cancer models in preclinical therapeutic discovery research. Furthermore, DACi sensitized and produced a synergistic effect with approved oncology therapeutics on inherently resistant MBC. This study introduced a role for DACi in suppressing the migratory and mesenchymal phenotype of MBC cells through regulation of the epithelial-mesenchymal transition axis and suppression of the CTC population. Preliminary evidence that DACi treatment in combination with MEK1/2 inhibitors exerts a synergistic effect on MBC cells was also demonstrated.

Metaplastic breast cancers frequently express immune checkpoint markers FOXP3 and PD-L1

BACKGROUND

Metaplastic breast carcinoma encompasses a heterogeneous group of tumours with differentiation into squamous and/or spindle, chondroid, osseous or rhabdoid mesenchymal-looking elements. Emerging immunotherapies targeting Programmed Death Ligand 1 (PD-L1) and immune-suppressing T cells (Tregs) may benefit metaplastic breast cancer patients, which are typically chemo-resistant and do not express hormone therapy targets.

METHODS

We evaluated the immunohistochemical expression of PD-L1 and FOXP3, and the extent of tumour infiltrating lymphocytes (TILs) in a large cohort of metaplastic breast cancers, with survival data.

RESULTS

Metaplastic breast cancers were significantly enriched for PD-L1 positive tumour cells, compared to triple-negative ductal breast cancers (P < 0.0001), while there was no significant difference in PD-L1 positive TILs. Metaplastic breast cancers were also significantly enriched for TILs expressing FOXP3, with FOXP3 positive intra-tumoural TILs (iTILs) associated with an adverse prognostic outcome (P = 0.0226). Multivariate analysis identified FOXP3 iTILs expression status as an important independent prognostic factor for patient survival.

CONCLUSIONS

Our findings indicate the clinical significance and prognostic value of FOXP3, PD-1/PD-L1 checkpoint and TILs in metaplastic breast cancer and confirm that a subset of metaplastics may benefit from immune-based therapies.

Whole-exome analysis of metaplastic breast carcinomas with extensive osseous differentiation

AIMS

Metaplastic breast carcinoma (MBC) is a rare type of triple-negative breast cancer that shows vast histological and genetic heterogeneity. Osseous differentiation can be found in different subtypes of MBC. Whether MBCs with osseous differentiation are underpinned by specific genetic alterations has yet to be defined. The aim of this study was to investigate the repertoire of somatic mutations and copy number alterations (CNAs) in three MBCs with extensive osseous differentiation.

METHODS AND RESULTS

Tumour and normal DNA samples from three MBCs with extensive osseous differentiation were subjected to whole-exome sequencing. Somatic mutations, CNAs and mutational signatures were determined by use of a validated bioinformatics pipeline. Our analyses revealed clonal TP53 hotspot mutations associated with loss of heterozygosity of the wild-type allele coupled with mutations affecting genes related to the Wnt and/or the phosphoinositide 3-kinase-AKT-mammalian target of rapamycin pathways in all cases analysed. All cases showed a dominant mutational signature 1, with two cases showing a secondary signature 3 in addition to other features of homologous recombination DNA repair defects. The oncostatin M receptor gene, which plays a role in mesenchymal differentiation and bone formation, was found to be mutated in two MBCs with extensive osseous differentiation and in none of 35 previously published 35 MBCs.

CONCLUSION

Our findings suggest that MBCs with osseous differentiation have somatic mutations similar to those of other forms of MBC.

Molecular Features of Metaplastic Breast Carcinoma: An Infrequent Subtype of Triple Negative Breast Carcinoma

Metaplastic breast carcinoma (MBC) is a heterogeneous group of infrequent invasive carcinomas that display differentiation of the neoplastic epithelium towards squamous cells and/or mesenchymal-type elements. Most MBC have a triple negative phenotype and poor prognosis. Thus, MBC have worse survival rates than other invasive breast carcinomas, including other triple negative breast carcinomas (TNBC). In this study, we reviewed the molecular features of MBC, pointing out the differences among subtypes. The most frequently mutated genes in MBC were TP53 and PIK3CA. Additionally, mutations in the other genes of the PI3K/AKT pathway indicated its importance in the pathogenesis of MBC. Regarding copy number variations (CNVs), MYC was the most frequently amplified gene, and the most frequent gene loss affected the CDKN2A/CDKN2B locus. Furthermore, the pattern of mutations and CNVs of MBC differed from those reported in other TNBC. However, the molecular profile of MBC was not homogeneous among histological subtypes, being the alterations in the PI3K pathway most frequent in spindle cell carcinomas. Transcriptomic studies have demonstrated an epithelial to mesenchymal program activation and the enrichment of stemness genes in most MBC. In addition, current studies are attempting to define the immune microenvironment of these tumors. In conclusion, due to specific molecular features, MBC have a different clinical behavior from other types of TNBC, being more resistant to standard chemotherapy. For this reason, new therapeutic approaches based on tumor molecular characteristics are needed to treat MBC.

SOX10 - A Novel Marker for the Differential Diagnosis of Breast Metaplastic Squamous Cell Carcinoma

Introduction

Differential diagnosis of metaplastic squamous cell carcinoma of breast (MSCCB) is difficult. In particular, in terms of metastatic MSCCB, because of the low speciality of traditional markers such as mammaglobin, gross cystic disease fluid protein-15 (GCDFP-15) and GATA binding protein 3 (GATA3), the most common problem is differentiating the spread of MSCCB to the lung from a primary lung squamous cell carcinoma. It is urgently required to explore a novel marker to aid in differential diagnosis.

Aim

The aim of this study is to explore a novel marker to aid in the differential diagnosis of MSCCB from other squamous cell carcinomas (SCC) in other organs.

Methods

We tested the expression of SOX10 in 375 human SCC specimens with immunohistochemistry (IHC).

Results

In a series of 20 MSCCB, 9 (45%) were positive for SOX10. All of them were triple-negative MSCCB. Conversely, SOX10 was totally negative in another 205 SCC originating from lung, skin, cervix, oral mucosa, and esophagus. In a series of 150 triple-negative breast cancer and their metastatic foci, SOX10 labeling in the primary tumor and metastasis was 78% and 79.3%, respectively, and the agreement rate was 97.3% (P>0.05).

Conclusion

Our findings demonstrate that SOX10 was recommended for differentiating MSCCB from non-mammary metastasis to the breast, as well as for distinguishing primary SCC from metastatic MSCCB, and SOX10 may be valuable in the pathological diagnosis of breast-derived metaplastic squamous cell carcinoma.

Digital spatial profiling application in breast cancer: a user's perspective

The disciplines of oncology and pathology are at present experiencing a wave of changes as precision medicine becomes embedded as standard-of-care. Consequently, the need to assess increasing numbers of biomarkers simultaneously has become more urgent and recognising the vast intra-tumoural heterogeneity, including within the microenvironment, requires a complex dimensional understanding of the localisation of the biomarker expression. Digital spatial profiling (DSP; nanoString™) technology spatially resolves and digitally quantifies proteins in a highly multiplexed assay, underpinned by the nCounter® barcoding platform. We present the application of this technology to breast cancer samples. Applying the 'off the shelf' cancer panel and a custom-conjugated E-cadherin antibody, we quantify vast intra-tumoural heterogeneity in immunological and tumour markers, and demonstrate a need for focussed selection of target cell populations. The technology offers enormous potential not only for making research advances but also for improving standard operating procedures in diagnostic applications.

Morphologic and Genomic Heterogeneity in the Evolution and Progression of Breast Cancer

: Breast cancer is a remarkably complex and diverse disease. Subtyping based on morphology, genomics, biomarkers and/or clinical parameters seeks to stratify optimal approaches for management, but it is clear that every breast cancer is fundamentally unique. Intra-tumour heterogeneity adds further complexity and impacts a patient's response to neoadjuvant or adjuvant therapy. Here, we review some established and more recent evidence related to the complex nature of breast cancer evolution. We describe morphologic and genomic diversity as it arises spontaneously during the early stages of tumour evolution, and also in the context of treatment where the changing subclonal architecture of a tumour is driven by the inherent adaptability of tumour cells to evolve and resist the selective pressures of therapy.

Breast Cancer: A Molecularly Heterogenous Disease Needing Subtype-Specific Treatments

Breast cancer is the most commonly occurring cancer in women. There were over two-million new cases in world in 2018. It is the second leading cause of death from cancer in western countries. At the molecular level, breast cancer is a heterogeneous disease, which is characterized by high genomic instability evidenced by somatic gene mutations, copy number alterations, and chromosome structural rearrangements. The genomic instability is caused by defects in DNA damage repair, transcription, DNA replication, telomere maintenance and mitotic chromosome segregation. According to molecular features, breast cancers are subdivided in subtypes, according to activation of hormone receptors (estrogen receptor and progesterone receptor), of human epidermal growth factors receptor 2 (HER2), and or BRCA mutations. In-depth analyses of the molecular features of primary and metastatic breast cancer have shown the great heterogeneity of genetic alterations and their clonal evolution during disease development. These studies have contributed to identify a repertoire of numerous disease-causing genes that are altered through different mutational processes. While early-stage breast cancer is a curable disease in about 70% of patients, advanced breast cancer is largely incurable. However, molecular studies have contributed to develop new therapeutic approaches targeting HER2, CDK4/6, PI3K, or involving poly(ADP-ribose) polymerase inhibitors for BRCA mutation carriers and immunotherapy.

Molecular Profiling of the Metaplastic Spindle Cell Carcinoma of the Breast Reveals Potentially Targetable Biomarkers

INTRODUCTION

Spindle cell carcinoma is a rare subtype of metaplastic breast cancer, with triple-negative (TNBC: estrogen receptor-negative/progesterone receptor-negative/human epidermal growth factor receptor 2-negative) phenotype. It is associated with a marked resistance to conventional chemotherapy and has an overall poor outcome.

MATERIALS AND METHODS

Twenty-three pure spindle cell carcinomas of the breast (18 primary and 5 recurrent/metastatic) were comprehensively explored for biomarkers of immuno-oncology and targeted therapies using immunohistochemistry and DNA/RNA sequencing.

RESULTS

The majority (21/23) of spindle cell carcinomas were TNBC. Estrogen and androgen receptor expression above the therapeutic thresholds were detected in 2 cases each. Pathogenic gene mutations were identified in 21 of 23 cases, including PIK3CA, TP53, HRAS, NF1, and PTEN. One case with matched pre- and post-chemotherapy samples exhibited a consistent mutational profile (PIK3CA and HRAS mutations) in both samples. Gene amplifications were present in 5 cases, including 1 case without detectable mutations. The spindle cell carcinomas cohort had consistently low total mutational burden (all below the 80th percentile for the entire TNBC cohort). All tumors were microsatellite stable. Programmed death-ligand 1 expression was observed on both tumor cells (in 7/21 cases), and in tumor-infiltrating immune cells (2/21 cases).

CONCLUSIONS

Spindle cell carcinomas are characterized by targetable molecular alterations in the majority of cases, but owing to the lack of uniform findings, individual patient profiling is necessary. Detection of individual combinations of biomarkers should improve treatment options for this rare but aggressive disease.

Combination of PI3K and MEK inhibitors yields durable remission in PDX models of PIK3CA-mutated metaplastic breast cancers

Background

Metaplastic breast cancer (MBC) is a rare form of breast cancer characterized by an aggressive clinical presentation, with a poor response to standard chemotherapy. MBCs are typically triple-negative breast cancers (TNBCs), frequently with alterations to genes of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways. The objective of this study was to determine the response to PI3K and MAPK pathway inhibitors in patient-derived xenografts (PDXs) of MBCs with targetable alterations.

Methods

We compared survival between triple-negative MBCs and other histological subtypes, in a clinical cohort of 323 TNBC patients. PDX models were established from primary breast tumors classified as MBC. PI3K-AKT-mTOR and RTK-MAPK pathway alterations were detected by targeted next-generation sequencing (NGS) and analyses of copy number alterations. Activation of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways was analyzed with reverse-phase protein arrays (RPPA). PDXs carrying an activating mutation of PIK3CA and genomic changes to the RTK-MAPK signaling pathways were treated with a combination consisting of a PI3K inhibitor and a MEK inhibitor.

Results

In our clinical cohort, the patients with MBC had a worse prognosis than those with other histological subtypes. We established nine metaplastic TNBC PDXs. Three had a pathogenic mutation of PIK3CA and additional alterations to genes associated with RTK-MAPK signaling. The MBC PDXs expressed typical EMT and stem cell genes and were of the mesenchymal or mesenchymal stem-like TNBC subtypes. On histological analysis, MBC PDXs presented squamous or chondroid differentiation. RPPA analysis showed activation of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways. In vivo, the combination of PI3K and MAPK inhibitors displayed marked antitumor activity in PDXs carrying genomic alterations of PIK3CA, AKT1, BRAF, and FGFR4.

Conclusion

The treatment of metaplastic breast cancer PDXs by activation of the PI3K-AKT-mTOR and RTK-MAPK pathways at the genomic and protein levels with a combination of PI3K and MEK inhibitors resulted in tumor regression in mutated models and may therefore be of interest for therapeutic purposes.

Structural analysis of healthy and cancerous epithelial-type breast cells by nanomechanical spectroscopy allows us to obtain peculiarities of the skeleton and junctions

The transition of healthy epithelial cells to carcinoma is associated with an alteration in the structure and organization of the cytoskeleton of the cells. A comparison of the mechanical properties of cancerous and healthy cells indicated a higher deformability of the cancer cells based on averaging the mechanical properties of single cells. However, the exact reason for softening of the cancerous cells compared to their counterparts remains unclear. Here, we focused on nanomechanical spectroscopy of healthy and cancerous ductal epithelial-type breast cells by means of atomic force microscopy with high lateral and depth precision. As a result, based on atomic force microscopy measurements formation of significantly fewer microtubules in cancerous cells which was observed in our study is most likely one of the main causes for the overall change in mechanical properties without any phenotypic shift. Strikingly, in a confluent layer of invasive ductal carcinoma cells, we observed the formation of cell-cell junctions that have the potential for signal transduction among neighboring cells such as desmosomes and adherens junctions. This increases the possibility of cancerous cell collaboration in malignancy, infiltration or metastasis phenomena.

Comparison of outcomes between metaplastic and triple-negative breast cancer patients

Purpose

Metaplastic breast cancer (MBC) is a rare, aggressive variant of breast cancer that has been associated with poor clinical outcomes, as has triple-negative breast (TNBC) cancer. Limited studies compare the clinical characteristics and prognosis of MBC to TNBC. This study uses a large, contemporary US cancer database to compare clinical characteristics and survival outcomes for patients with MBC to those with TNBC.

Methods

The National Cancer Database was queried for women with cT1-4N1-3M0 MBC or TNBC diagnosed between 2004 and 2013 and treated with definitive surgery. Chi-squared analysis was performed to determine differences between the cohorts. Kaplan-Meier curves compared overall survival (OS), and Cox regression determined patient factors associated with OS.

Results

Altogether, 55,847 patients met the inclusion criteria; 50,705 (90.8%) had TNBC and 5,142 (9.2%) had MBC. Most patients had no comorbid conditions (82%), N0 disease (71%), poorly differentiated histology (77%), received chemotherapy (87%), and received radiation therapy (60%). Amongst all patients, patients with TNBC disease were observed to have greater OS than those with MBC (5-year OS 72.0% vs 55.8%, p < 0.001). The greater observed OS for patients with TNBC persisted when controlling for stage and when comparing propensity score matched cohorts. On Cox regression, lower age, T1 status, N0 status, chemotherapy, TNBC disease, and radiation therapy (RT) were associated with improved OS.

Conclusions

MBC had an association with poorer OS compared to TNBC, while RT and chemotherapy receipt were associated with improved OS for patients regardless of stage. Further studies are needed to corroborate the conclusions herein.

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Metaplastic breast cancer is associated with poor clinical outcomes.

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Metaplastic breast cancer associated with worse survival than patients with triple negative invasive ductal carcinoma.

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Radiation therapy and chemotherapy associated with improved survival for patients with metaplastic breast cancer.

Breast cancer

Breast cancer is the most frequent malignancy in women worldwide and is curable in ~70-80% of patients with early-stage, non-metastatic disease. Advanced breast cancer with distant organ metastases is considered incurable with currently available therapies. On the molecular level, breast cancer is a heterogeneous disease; molecular features include activation of human epidermal growth factor receptor 2 (HER2, encoded by ERBB2), activation of hormone receptors (oestrogen receptor and progesterone receptor) and/or BRCA mutations. Treatment strategies differ according to molecular subtype. Management of breast cancer is multidisciplinary; it includes locoregional (surgery and radiation therapy) and systemic therapy approaches. Systemic therapies include endocrine therapy for hormone receptor-positive disease, chemotherapy, anti-HER2 therapy for HER2-positive disease, bone stabilizing agents, poly(ADP-ribose) polymerase inhibitors for BRCA mutation carriers and, quite recently, immunotherapy. Future therapeutic concepts in breast cancer aim at individualization of therapy as well as at treatment de-escalation and escalation based on tumour biology and early therapy response. Next to further treatment innovations, equal worldwide access to therapeutic advances remains the global challenge in breast cancer care for the future.

A Molecular and Morphological Deep-Dive Into Metaplastic Breast Cancers

Metaplastic breast cancers (MBC) are relatively rare but account for significant global breast cancer mortality. Typically presenting without oestrogen and progesterone receptors or HER2 expression, these triple negative breast cancers are the archetypal ‘stem cell-like’ tumours that show a variety of metaplastic elements, including squamous, spindle, and chondroid. Given the vast heterogeneity in MBC by definition, large cohort studies are needed to draw conclusions. Together with our consortium colleagues, a cohort of 347 MBC was established, and a detailed morphological assessment made in an effort to understand the clinical relevance of the current diagnostic guidelines. Biomarker expression was investigated, and whole exome sequencing was performed. Herein, we provide an overview and contextualisation of the study.

Recent advances in breast cancer research impacting clinical diagnostic practice

During the last decade, the genomics revolution has driven critical advances in molecular oncology and pathology, and a deeper appreciation of heterogeneity that is beginning to reshape our thinking around diagnostic classification. Recent developments have seen existing classification systems modified and improved where possible, gene-based diagnostics implemented and tumour-immune interactions modulated. We present a detailed discussion of this progress, including advances in the understanding of breast tumour classification, e.g. mixed ductal-lobular tumours and the spectrum of triple-negative breast cancer. The latest information on clinical trials and the implementation of gene-based diagnostics, including MammaPrint and Oncotype Dx and others, is synthesised, and emerging targeted therapies, as well as the burgeoning immuno-oncology field, and their relevance in breast cancer, are discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.