Metaplastic carcinomas of the breast: diagnostic challenges and new translational insights

Translational Aspects in Metaplastic Breast Carcinoma

Breast cancer is the most common cancer among women. Metaplastic breast carcinoma (MpBC) is a rare, heterogeneous group of invasive breast carcinomas, which are classified as predominantly triple-negative breast carcinomas (TNBCs; HR-negative/HER2-negative). Histologically, MpBC is classified into six subtypes. Two of these are considered low-grade and the others are high-grade. MpBCs seem to be more aggressive, less responsive to neoadjuvant chemotherapy, and have higher rates of chemoresistance than other TNBCs. MpBCs have a lower survival rate than expected for TNBCs. MpBC treatment represents a challenge, leading to a thorough exploration of the tumor immune microenvironment, which has recently opened the possibility of new therapeutic strategies. The epithelial-mesenchymal transition in MpBC is characterized by the loss of intercellular adhesion, downregulation of epithelial markers, underexpression of genes with biological epithelial functions, upregulation of mesenchymal markers, overexpression of genes with biological mesenchymal functions, acquisition of fibroblast-like (spindle) morphology, cytoskeleton reorganization, increased motility, invasiveness, and metastatic capabilities. This article reviews and summarizes the current knowledge and translational aspects of MpBC.

Detailed DNA methylation characterisation of phyllodes tumours identifies a signature of malignancy and distinguishes phyllodes from metaplastic breast carcinoma

Phyllodes tumours (PTs) are rare fibroepithelial lesions of the breast that are classified as benign, borderline, or malignant. As little is known about the molecular underpinnings of PTs, current diagnosis relies on histological examination. However, accurate classification is often difficult, particularly for distinguishing borderline from malignant PTs. Furthermore, PTs can be misdiagnosed as other tumour types with shared histological features, such as fibroadenoma and metaplastic breast cancers. As DNA methylation is a recognised hallmark of many cancers, we hypothesised that DNA methylation could provide novel biomarkers for diagnosis and tumour stratification in PTs, whilst also allowing insight into the molecular aetiology of this otherwise understudied tumour. We generated whole-genome methylation data using the Illumina EPIC microarray in a novel PT cohort (n = 33) and curated methylation microarray data from published datasets including PTs and other potentially histopathologically similar tumours (total n = 817 samples). Analyses revealed that PTs have a unique methylome compared to normal breast tissue and to potentially histopathologically similar tumours (metaplastic breast cancer, fibroadenoma and sarcomas), with PT-specific methylation changes enriched in gene sets involved in KRAS signalling and epithelial-mesenchymal transition. Next, we identified 53 differentially methylated regions (DMRs) (false discovery rate < 0.05) that specifically delineated malignant from non-malignant PTs. The top DMR in both discovery and validation cohorts was hypermethylation at the HSD17B8 CpG island promoter. Matched PT single-cell expression data showed that HSD17B8 had minimal expression in fibroblast (putative tumour) cells. Finally, we created a methylation classifier to distinguish PTs from metaplastic breast cancer samples, where we revealed a likely misdiagnosis for two TCGA metaplastic breast cancer samples. In conclusion, DNA methylation alterations are associated with PT histopathology and hold the potential to improve our understanding of PT molecular aetiology, diagnostics, and risk stratification. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Metaplastic Breast Carcinoma Revisited; Subtypes Determine Outcomes: Comprehensive Pathologic, Clinical, and Molecular Review

Metaplastic breast carcinoma (MpBC) is a heterogeneous group of tumors that clinically could be divided into low risk and high risk. It is important to recognize the different types of MpBC, as the high-risk subtypes have worse clinical outcomes than triple-negative breast cancer. It is important for the pathologist to be aware of the MpBC entities and use the proposed algorithms (morphology and immunohistochemistry) to assist in rendering the final diagnosis. Few pitfalls are discussed, including misinterpretation of immunohistochemistry and certain histomorphologies, particularly spindle lesions associated with complex sclerosing lesions.

A huge metaplastic breast carcinoma with chest wall invasion and pulmonary metastasis: a rare case report

Metaplastic breast carcinoma (MBC) is a diverse group of invasive breast carcinoma, in which the neoplastic epithelium differentiates toward squamous cells or mesenchymal looking elements, including but not restricted to spindle, osseous and chondroid cells. MBC was formally considered a distinct pathological pattern by WHO classification of breast tumors in 2000. We report the case of a 49-year-old Syrian female who presented to our hospital due to a painful huge mass in her right breast. Radiographic and clinical findings were highly indicative of breast carcinoma. Therefore, a core needle biopsy was performed, and surprisingly, microscopic examination suggested the diagnosis of soft tissue sarcoma, whereas immune stains confirmed the diagnosis of metaplastic carcinoma. We aim to introduce a challenging case that clarifies the rarity of this tumor, and the methods we used in diagnosing, examining and treating this malignancy.

Metaplastic Breast Carcinoma Revisited; Subtypes Determine Outcomes: Comprehensive Pathologic, Clinical, and Molecular Review

Metaplastic breast carcinoma (MpBC) is a heterogeneous group of tumors that clinically could be divided into low risk and high risk. It is important to recognize the different types of MpBC, as the high-risk subtypes have worse clinical outcomes than triple-negative breast cancer. It is important for the pathologist to be aware of the MpBC entities and use the proposed algorithms (morphology and immunohistochemistry) to assist in rendering the final diagnosis. Few pitfalls are discussed, including misinterpretation of immunohistochemistry and certain histomorphologies, particularly spindle lesions associated with complex sclerosing lesions.

The matricellular protein CCN6 differentially regulates mitochondrial metabolism in normal epithelium and in metaplastic breast carcinomas

Metaplastic breast carcinoma (MBC) is an aggressive subtype of triple negative breast cancer with undefined precursors, limited response to chemotherapy, and frequent distant metastasis. Our laboratory has reported that CCN6/WISP3, a secreted protein that regulates growth factor signaling, is downregulated in over 85% of MBCs. Through generation of a mammary epithelial cell-specific Ccn6 knockout mouse model (MMTV-cre;Ccn6^fl/fl) we have demonstrated that CCN6 is a tumor suppressor for MBC; MMTV-cre;Ccn6^fl/fl mice develop tumors recapitulating the histopathology and proteogenomic landscape of human MBC, but the mechanisms need further investigation. In this study, we report that preneoplastic mammary glands of 8-week-old MMTV-Cre;Ccn6^fl/fl female mice show significant downregulation of mitochondrial respiratory chain genes compared to controls, which are further downregulated in MBCs of MMTV-Cre;Ccn6^fl/fl mice and humans. We found that CCN6 downregulation in non-tumorigenic breast cells reduces mitochondrial respiration and increases resistance to stress-induced apoptosis compared to controls. Intracellular ectopic CCN6 protein localizes to the mitochondria in MDA-MB-231 mesenchymal-like breast cancer cells, increases mitochondrial respiration and generation of reactive oxygen species, and reverses doxorubicin resistance of MBC cells. Our data highlight a novel function of CCN6 in the regulation of redox states in preneoplastic progression and suggest potential preventative and treatment strategies against MBC based on CCN6 upregulation.

Complex Fibroadenoma with Pronounced Squamous Metaplasia: A Rare Case Report, Differential Diagnostic Considerations, and Associated Breast Cancer Risk

Squamous metaplasia of the breast is a rare and unusual finding. A number of benign and malignant differential entities exist when squamous cells are present in a breast lesion. Our patient was found to have pronounced squamous metaplasia and keratin cysts arising in a complex fibroadenoma. The rare nature of squamous metaplasia arising in such a lesion poses some diagnostic challenges, as squamous epithelium and squamous metaplasia in the breast may raise suspicion for malignancy. Herein we present a unique case and discussion of benign and malignant differential entities. We also retrospectively reviewed a series of complex fibroadenomas in our institution, including the demographic and histologic features, and more importantly the associated breast cancer risk.

Metaplastic breast carcinoma: a retrospective study of 26 cases

Metaplastic breast carcinoma is a rare invasive breast cancer. Metaplastic breast carcinoma is mainly characterized by an epithelial or mesenchymal cell population mixed with adenocarcinoma. We collected 26 cases of metaplastic breast carcinoma in the First Affiliated Hospital of Bengbu Medical College from 2008 to 2014. Tumor size, tumor grade, vascular invasion, ER/PR status, histologic classification, and HER2/neu status were assessed for all cases and the literature was reviewed. Clinicopathologic characteristics of patients diagnosed with metaplastic breast carcinomas and its key points of differential diagnosis were discussed. All patients were female, with the median age of 50 years. The mean tumor size was 3.2 cm. 4 subtypes of metaplastic breast carcinomas were documented. Fibromatosis-like metaplastic carcinomas are typically characterized by wavy, intertwined, gentle spindle cells. When the tumor components are almost squamous cell carcinoma components and the primary squamous cell carcinoma of other organs and tissues are excluded, we can diagnose breast squamous cell carcinoma. In spindle cell carcinoma, atypical spindle cells are arranged in many ways and are usually accompanied by inflammatory cell infiltrate. Cancer with interstitial differentiation has mixed malignant epithelial and mesenchymal differentiation, and the mesenchymal components are diverse. Most tumors are triple negative. At present, surgical resection combined with chemotherapy or radiation therapy is the most effective and acceptable method for treating metaplastic breast carcinoma.

Malignant phyllodes tumor with liposarcomatous differentiation: Diagnosed on cytology

Phyllodes tumor (PT) accounts for less than 1% of all primary tumors of the breast and 2% to 3% of all fibroepithelial lesions. We report a case of heterologous liposarcomatous elements in a malignant PT of the breast on Fine needle aspiration cytology (FNAC) and later confirmed by histopathological examination. A 58-years-old woman presented with a huge breast mass for which FNAC was done. Cytology showed features of malignant PT with a good representation of heterologous liposarcomatous areas. The cytological findings were in concordance with the histologic features. Malignant PT and its various heterologous elements of stroma can be diagnosed on FNA cytology when performed optimally. They can be vital for the preoperative assessment of patients suspected with malignancy to formulate the surgical plan accordingly.

When Something Seems Amiss: Radiology-Pathology Correlation of Metaplastic Breast Cancer

Metaplastic breast cancer is difficult to diagnose, resistant to conventional treatment, and biologically aggressive. A suspicious timeline and discordance between imaging findings and histopathologic tissue diagnosis should trigger additional workup. New, large lesions or rapidly growing lesions with complex echogenicity on ultrasound warrant correlation with image-guided biopsy for a definitive diagnosis. Lesions that appear aggressive on imaging, with negative biopsy findings, may represent false negatives due to sampling bias from intratumoral heterogeneity. In such cases, it may be advisable to obtain an excisional biopsy. These tumors are known to progress even with neoadjuvant chemotherapy. Immunotherapy, however, may be effective even for metastatic disease. A multidisciplinary approach and a high index of suspicion may, therefore, confer survival benefits in circumstances where the imaging phenotype does not fit with the timeline or pathologic diagnosis. This report describes five cases of metaplastic breast cancer diagnosed at our institution to highlight the importance of a timely and accurate diagnosis of this rare but aggressive breast malignancy.

Recurrent borderline phyllodes tumor in nipple: a rare case report and review of the literature

Phyllodes tumor (PT) of the breast is a rare tumor. They are usually located in the four quadrants of the mammary gland and may also appear below the nipple. Although there have been a number of cases reported, here we report a very rare case of this tumor in an unusual location. The patient has been diagnosed with right breast borderline PT, who accepted breast-conserving surgery. Twelve months after surgery we found right nipple enlargement, without nipple discharge, ipsilateral and contralateral breast without palpable mass. Interestingly, ultrasound showed a lesion in the right nipple: a hypoechoic mass with a diameter of 2.0 cm was seen in the nipple, with no significant calcification. The patient underwent nipple-sparing mastectomy without postoperative adjuvant radiotherapy. Histopathological and immunohistochemical analysis demonstrated a borderline PT. There were no signs of recurrence after two years of follow-up. We consider that wide surgical resection and negative margin are still the main methods for the treatment of recurrent borderline PTs.

Metaplastic Breast Carcinoma: Update on Histopathology and Molecular Alterations

CONTEXT—

Metaplastic carcinoma is a rare, triple-negative carcinoma of the breast that exhibits transformation of part or all of its glandular carcinomatous component into a nonglandular, or metaplastic, component. The World Health Organization currently recognizes 5 variants of metaplastic carcinoma based on their histologic appearance.

OBJECTIVE—

To review the histologic classifications, differential diagnosis, prognosis, and recent laboratory studies of metaplastic breast carcinoma.

DATA SOURCES.—

We reviewed recently published studies that collectively examine metaplastic carcinomas, including results from our own research.

CONCLUSIONS.—

Metaplastic breast carcinoma has a broad spectrum of histologic patterns, often leading to a broad differential diagnosis. Diagnosis can typically be rendered by a combination of morphology and immunohistochemical staining for high-molecular-weight cytokeratins and p63. Recent studies elucidate new genes and pathways involved in the pathogenesis of metaplastic carcinoma, including the downregulation of CCN6 and WNT pathway gene mutations, and provide a novel MMTV-Cre;Ccn6^fl/fl knockout disease-relevant mouse model to test new therapies.

Cellular Spindled Histiocytic Pseudotumor: A Benign Mimic of Spindle Cell Neoplasia of the Breast

CONTEXT.—

Cellular spindled histiocytic pseudotumor (CSHPT) is an exuberant, dense histiocytic proliferation seen in the setting of mammary fat necrosis. CSHPT has a broad histologic differential diagnosis, including benign, malignant, and inflammatory etiologies.

OBJECTIVES.—

To highlight the most important histologic and immunohistochemical findings of CSHPT and provide comparisons to entities within the broad differential diagnosis.

DATA SOURCES.—

Recently published literature regarding CSHPT and other diagnostic considerations.

CONCLUSIONS.—

CSHPT is a benign histiocytic proliferation with a broad differential diagnosis, for which comprehensive ancillary studies may be required to exclude malignant and infectious entities.

Transcatheter arterial chemoembolization improves the resectability of malignant breast phyllodes tumor with angiosarcoma component: a case report

Background

A giant phyllodes tumor of the breast is a rare fibroepithelial lesion, and its treatment is controversial. Many case reports have reported performing skin graft reconstruction after tumor excision. Chest wall resection may be required if the tumor has invaded the chest muscle layer. We speculated that transcatheter arterial chemoembolization (TACE) can improve the resectability of malignant phyllodes tumor of the breast without requiring skin grafting. The English literature contains only one case report similar to our experience.

Case presentation

We report a rare case of a 51-year-old woman who had a giant malignant phyllodes tumor with heterologous sarcomatous differentiation in her right breast. The tumor was 19.43 × 12.98 × 21.47 cm. Whole-body computed tomography (CT) and bone scan did not reveal distant metastasis. Chest magnetic resonance imaging showed chest wall tumor invasion. Considering that skin defects after mastectomy can be extensive, we administered four courses of chemoembolization in the 5 weeks before surgery (30 mg of epirubicin and embozene microspheres [400, 500, and 700 μm]/week). Each process was well tolerated, with no serious complications. Only fever and local pain at the tumor site were noted, and these symptoms resolved with time. The follow-up CT scan showed a 45% reduction in tumor volume. Therefore, simple mastectomy was performed without skin grafting reconstruction. Wound healing was satisfactory, and the patient was discharged 1 week after surgery. Pathological and immunohistochemistry (IHC) findings showed a malignant phyllodes tumor with an angiosarcoma component. Because of tumor invasion of the chest wall, we recommended the patient receive radiotherapy, but she refused. Two months after surgery, recurrence of the malignant phyllodes tumor with right axillary lymph node involvement and lung metastasis was confirmed.

Conclusion

Initial surgical resection of giant phyllodes tumors is often challenging. For initial presentation with unresectable giant phyllodes tumor, we recommend to perform TACE prior to surgery. In our patient, preoperative TACE was effective and safe. If the tumor has invaded the chest wall, early radiotherapy after surgery may be recommended for preventing recurrence.

Metaplastic Carcinoma of Breast: Case Series with Cytohistological Correlation

Metaplastic carcinoma of breast (MCB) is a rare breast malignancy. It is important to differentiate metaplastic carcinoma from malignant phyllodes and primary breast sarcomas because of their differing biological behavior and prognosis. We report four cases of MCB diagnosed over the past 15 years. Retrospective review of patient records in a tertiary care setting to retrieve cases diagnosed as MCB. Patient records of the past 15 years (2002–2015) were retrieved. Four histopathologically diagnosed cases of metaplastic carcinoma out of a total of 880 archived cases of breast carcinoma were studied along with their cytopathology. Immunohistochemistry was performed on sections. MCB comprised 0.45% of all breast malignancies. The four cases of MCB included MCB with chondroid metaplasia, spindle cell carcinoma, adenosquamous carcinoma, and carcinosarcoma. All the tumors were invariably triple negative (estrogen receptor, progesterone receptor, and Her2/Neu negative) and expression of other epithelial and mesenchymal markers was variable. MCB is a rare breast malignancy. Differential diagnosis is related to the presence of heterologous elements and degree of atypia seen in the lesion. It is important to be aware of this entity as it carries a poor prognosis.

A Comparative Review of Mixed Mammary Tumors in Mammals

Mixed tumors are characterized by the histological identification of two or more cell types. Commonly, a mixture of epithelial and myoepithelial cells is included in abundant stroma, which can consist of myxoid, chondroid or bony matrices. Spontaneously arising mixed tumors are rare lesions in the human breast but are common in human salivary glands and canine mammary glands. Subtle histopathological characteristics and overlapping attributes of malignant lesions with other benign lesions can lead to a diagnostic challenge. Mixed tumors can present as benign or malignant. While malignant mixed tumors are quite rare in the human breast they have a poor prognosis. Benign mixed mammary tumors occur more frequently in female dogs than in humans and are usually associated with a good prognosis. This review will provide a comprehensive overview of mixed mammary tumors, across various mammalian species.

Fibromatosis-like metaplastic carcinoma of breast: a challenge for clinicopathologic diagnosis

Fibromatosis-like metaplastic carcinoma of breast (FLMC) is a newly described metaplastic tumor in the (4th) edition of the WHO classification of breast tumors in 2012. It is a low-grade tumor formed by spindle cells with mild or absent nuclear atypia, embedded in collagenized stroma, and it has only <5% tumor cells showing epithelial traits. Because its biological behavior is better than that of general spindle cell metaplastic cancer, this cancer type is added to the new WHO classification. Due to their mild morphology, breast FLMCs are often misdiagnosed as benign interstitial proliferative lesions or benign mesenchymal tumors. Accurate diagnosis is a challenging task particularly in needle core biopsies. We systematically reviewed 23 cases of metaplastic breast carcinoma (MBC), 8 cases of metaplastic carcinoma with squamous cell component, 12 cases of spindle cell/sarcomatoid metaplastic carcinoma, and 3 cases of FLMC. Also, we performed CK, CK high molecular weight (34βE12), CK7, CK5/6, P63, CD10, ER, PR, HER-2, SMA, Desmin, CD34, CD117, and S-100 immunohistochemistry, using Envision staining. This study was focused on clinical and pathological features of 3 FLMC cases and assessed the immunoprofile of MBC subtypes in a large series to improve the understanding of these diseases.

Metaplastic Breast Cancer Treatment and Outcomes in 2500 Patients: A Retrospective Analysis of a National Oncology Database

BACKGROUND

Metaplastic breast cancer (MBC) is characterized by chemoresistance and hematogenous spread. We sought to identify factors associated with improved MBC outcomes and increased likelihood of MBC diagnosis.

METHODS

Women ≥ 18 years of age with stage I-III MBC and non-MBC diagnosed between 2010 and 2014 were identified in the National Cancer Data Base. Kaplan-Meier and multivariate Cox proportional hazards models were used to estimate associations with overall survival (OS). Multivariate logistic regression identified factors associated with MBC diagnosis.

RESULTS

Overall, 2451 MBC and 568,057 non-MBC patients were included; 70.3% of MBC vs. 11.3% of non-MBC patients were triple negative (p < 0.001). Five-year OS was reduced among MBC vs. non-MBC patients for the entire cohort (72.7 vs. 87.5%) and among triple-negative patients (71.1 vs. 77.8%; both p < 0.001). In MBC, triple-negative (vs. luminal) subtype was not associated with worse OS (hazard ratio [HR] 1.16, 95% confidence interval [CI] 0.88-1.54, p = 0.28). Compared with non-MBC patients, MBC patients were more likely to receive mastectomy (59.0 vs. 44.9%), chemotherapy (74.1 vs. 43.1%), and axillary lymph node dissection (ALND; 35.2 vs. 32.2%, all p ≤ 0.001). MBC patients more frequently had negative ALND (pN0) than non-MBC patients (20.0 vs. 10.6%, p < 0.001). Among MBC patients, chemotherapy (HR 0.69, 95% CI 0.53-0.89, p = 0.004) and radiotherapy (HR 0.52, 95% CI 0.39-0.69, p < 0.001) were associated with improved survival, while ALND was associated with decreased survival (HR 1.37, 95% CI 1.06-1.77, p = 0.02).

CONCLUSIONS

MBC patients had worse survival than non-MBC patients, independent of receptor status, suggesting that MBC may confer an additional survival disadvantage. Multimodal therapy was associated with improved outcomes, but ALND was not and may be overutilized in MBC.

Management of the axilla in metaplastic breast carcinoma

Background

Metaplastic breast cancer (MBC), characterized by admixed epithelial, squamous or mesenchymal elements, constitutes <1% of breast cancers and has a poor prognosis but a paradoxically low reported rate of axillary lymph node (LN) involvement. Due to its rarity, data on appropriate axillary management is lacking, prompting this investigation of LN status and outcomes.

Methods

We identified 41 MBC patients treated at our institution 2001-2011 who were followed for a median of 66 months. Statistical analyses evaluated axillary ultrasound (AUS), fine needle aspiration (FNA), and sentinel LN biopsy (SLNB) in association with LN status.

Results

Median tumor size was 2.7 cm and 76% were triple-negative. Twenty-three patients (56%) had preoperative AUS: 9 (39%) showed ≥1 suspicious LN, 6 proceeded to LN FNA and 3 were confirmed positive. Six patients had neoadjuvant chemotherapy, including 2 FNA LN+. Ten patients were LN+ at operation. Among 19 patients undergoing AUS and axillary surgery, AUS ± FNA sensitivity was 100% and specificity was 94%. LN positivity correlated with increasing tumor size, grade and angiolymphatic invasion. 16 patients recurred, 63% with distant disease (10/16) and one with isolated axillary disease after a negative SLNB not preceded by AUS. Overall SLNB accuracy was 96% (23/24), but absent preoperative AUS, 1/7 (14%) of SLNBs were falsely negative.

Conclusions

Our study is the first to specifically address the performance and utility of AUS/FNA and SLNB for MBC patients. AUS/FNA at diagnosis followed by SLN surgery provided accurate nodal staging and critical prognostic information to inform treatment recommendations. We recommend this approach for axillary management of MBC patients.

Rare variant of metaplastic carcinoma of the breast: a case report and review of the literature

Background

Metaplastic carcinoma encompasses a group of neoplasms characterized by differentiation of the neoplastic epithelium into squamous cells and/or mesenchymal-looking elements. Spindle cell carcinoma is a rare variant of this special histological type. Its prognosis remains poor, with a high rate of local recurrence and distant metastasis. To date, only a small number of cases have been described. There is no clear agreement on this histological subtype.

Case presentation

We report a case of a 53-year-old Moroccan woman who consulted our institution following palpation of a nodule of the left breast. Mammography in combination with breast ultrasonography revealed a lesion classified as Breast Imaging Reporting and Data System 4 with microcalcification. The patient was diagnosed with spindle cell carcinoma of the breast. The diagnosis was based primarily on histological and immunohistochemical studies of the breast biopsy and secondarily on the surgical specimen. No local or distant metastasis was found. The treatment used was total surgical excision followed by radiotherapy.

Conclusions

We describe the features (epidemiological, clinical, histological, immunohistochemical, and therapeutic outcomes) of our patient’s case and compare them with literature data.

Matricellular CCN6 (WISP3) protein: a tumor suppressor for mammary metaplastic carcinomas

Located at 6q22-23, Ccn6 (WISP3) encodes for a matrix-associated protein of the CCN family, characterized by regulatory, rather than structural, roles in development and cancer. CCN6, the least studied member of the CCN family, shares the conserved multimodular structure of CCN proteins, as well as their tissue and cell-type specific functions. In the breast, CCN6 is a critical regulator of epithelial-to-mesenchymal transitions (EMT) and tumor initiating cells. Studies using human breast cancer tissue samples demonstrated that CCN6 messenger RNA and protein are expressed in normal breast epithelia but reduced or lost in aggressive breast cancer phenotypes, especially inflammatory breast cancer and metaplastic carcinomas. Metaplastic carcinomas are mesenchymal-like triple negative breast carcinomas, enriched for markers of EMT and stemness. RNAseq analyses of the TCGA Breast Cancer cohort show reduced CCN6 expression in approximately 50% of metaplastic carcinomas compared to normal breast. Our group identified frameshift mutations of Ccn6 in a subset of human metaplastic breast carcinoma. Importantly, conditional, mammary epithelial-cell specific ccn6 (wisp3) knockout mice develop invasive high-grade mammary carcinomas that recapitulate human spindle cell metaplastic carcinomas, demonstrating a tumor suppressor function for ccn6. Our studies on CCN6 functions in metaplastic carcinoma highlight the potential of CCN6 as a novel therapeutic approach for this specific type of breast cancer.

MMTV-cre;Ccn6 knockout mice develop tumors recapitulating human metaplastic breast carcinomas

Metaplastic breast carcinoma is an aggressive form of invasive breast cancer with histological evidence of epithelial to mesenchymal transition (EMT). However, the defining molecular events are unknown. Here we show that CCN6 (WISP3), a secreted matricellular protein of the CCN (CYR61/CTGF/NOV) family, is significantly down regulated in clinical samples of human spindle cell metaplastic breast carcinoma. We generated a mouse model of mammary epithelial-specific Ccn6 deletion by developing a floxed Ccn6 mouse which was bred with an MMTV-Cre mouse. Ccn6^fl/fl; MMTV-Cre mice displayed severe defects in ductal branching and abnormal age-related involution compared to littermate controls. Ccn6^fl/fl ;MMTV-Cre mice developed invasive high grade mammary carcinomas with bona fide EMT, histologically similar to human metaplastic breast carcinomas. Global gene expression profiling of Ccn6^fl/fl mammary carcinomas and comparison of orthologous genes with a human metaplastic carcinoma signature revealed a significant overlap of 87 genes (p=5×10⁻¹¹). Among the shared deregulated genes between mouse and human are important regulators of epithelial morphogenesis including Cdh1, Ck19, Cldn3 and 4, Ddr1, and Wnt10a. These results document a causal role for Ccn6 deletion in the pathogenesis of metaplastic carcinomas with histological and molecular similarities with human disease. We provide a platform to study new targets in the diagnosis and treatment of human metaplastic carcinomas, and a new disease relevant model in which to test new treatment strategies.

Step by step approach to rare breast lesions containing spindle cells

Differential diagnosis of spindle cell lesions of breast is challenging for certain reasons. The most important reason is the presence of cytological atypia and mitosis in all three conditions: reactive, benign, and malignant. Patients diagnosed with benign and malignant tumor/tumor-like lesions that had spindle cell components following the histopathological examination were included in the study. The patients’ medical records were accessed to obtain the clinical history, follow-up notes, and radiological findings. Following histopathological, immunohistochemical, and clinical evaluations, the patients were diagnosed as follows: pseudoangiomatous stromal hyperplasia (PASH), bilateral desmoid-type fibromatosis (FM), adenomyoepithelioma (AME), myofibroblastoma (MFB), malignant phyllodes tumor (MF), high-grade AS, post-chemotherapy osteosarcoma (OS) + Paget’s disease, and metaplastic carcinoma (MC). An algorithmic approach should be used in the diagnosis; cellular structure, presence and grade of atypia, growth pattern, mitotic activity, immunohistochemical staining, and clinical and radiological features should be evaluated together. Detection of some molecular changes can be useful in differential diagnosis.

Genomic profiling of advanced-stage, metaplastic breast carcinoma by next-generation sequencing reveals frequent, targetable genomic abnormalities and potential new treatment options

CONTEXT

Metastatic metaplastic breast carcinoma (MPBC) is an uncommon, but aggressive, tumor resistant to conventional chemotherapy.

OBJECTIVE

To learn whether next-generation sequencing could identify potential targets of therapy for patients with relapsed and metastatic MPBC.

DESIGN

Hybridization capture of 3769 exons from 236 cancer-related genes and 47 introns of 19 genes commonly rearranged in cancer was applied to a minimum of 50 ng of DNA extracted from 20 MPBC formalin-fixed, paraffin-embedded specimens and sequenced to high uniform coverage.

RESULTS

The 20 patients with MPBC had a median age of 62 years (range, 42-86 years). There were 9 squamous (45%), 9 chondroid (45%), and 2 spindle cell (10%) MPBCs, all of which were high grade. Ninety-three genomic alterations were identified, (range, 1-11) with 19 of the 20 cases (95%) harboring an alteration that could potentially lead to a targeted treatment option. The most-common alterations were in TP53 (n = 69; 75%), PIK3CA (n = 37; 40%), MYC (n = 28; 30%), MLL2 (n = 28; 30%), PTEN (n = 23; 25%), CDKN2A/B (n = 19; 20%), CCND3 (n = 14; 15%), CCNE1 (n = 9; 10%), EGFR (n = 9; 10%), and KDM6A (n = 9; 10%); AKT3, CCND1, CCND2, CDK4, FBXW7, FGFR1, HRAS, NF1, PIK3R1, and SRC were each altered in a single case. All 16 MPBCs (100%) that were negative for ERBB2 (HER2) overexpression by immunohistochemistry and/or ERBB2 (HER2) amplification by fluorescence in situ hybridization were also uniformly (100%) negative for ERBB2 amplification by next-generation sequencing-based copy-number assessment.

CONCLUSIONS

Our results indicate that genomic profiling using next-generation sequencing can identify clinically meaningful alterations that have the potential to guide targeted treatment decisions in most patients with metastatic MPBC.

Low-Grade Fibromatosis-like Spindle Cell Carcinoma of the Breast

Low-grade fibromatosis-like spindle cell carcinoma is a rare tumor in the breast, and represents a variant of the very heterogeneous group of metaplastic carcinomas of the breast. These tumors warrant distinction because of their resemblance to pure fibromatosis, their propensity for local recurrence, and their favorable prognosis among the metaplastic carcinomas of the breast. The diagnosis is potentially challenging, particularly on core needle biopsies, because of the morphologic overlap with other low-grade spindle cell lesions. Recognition of a proliferation of cytologically bland spindle cells with areas of epithelial differentiation in combination with immunohistochemistry using antibodies against cytokeratins and myoepithelial markers should aid in producing a definitive diagnosis. These tumors can be locally aggressive with an increased incidence of local recurrence, but the potential for lymph node or distant metastasis is low. Complete excision with adequate margins is considered curative in the majority of cases.

Application of immunohistochemistry in breast pathology: a review and update

CONTEXT

Immunohistochemistry is a valuable tool in routine breast pathology, used for both diagnostic and prognostic parameters. The diagnostic immunomarkers are the scope of this review. Most breast lesions can be diagnosed on routine hematoxylin-eosin sections; however, in several scenarios, such as morphologically equivocal cases or metastatic tumors of unknown primary, the appropriate application of immunohistochemistry adds true value in reaching an accurate diagnosis.

OBJECTIVE

To evaluate the diagnostic utility of the most commonly studied immunomarkers in the field of breast pathology by review of the literature, using the database of indexed articles in PubMed (US National Library of Medicine, Bethesda, Maryland) from 1976 to 2013.

DATA SOURCES

Literature review, and author's research data and personal practice experience.

CONCLUSIONS

The appropriate use of immunohistochemistry by applying a panel of immunomarkers and using a standardized technical and interpretational method will complement the morphologic assessment and aid in the accurate classification of difficult breast lesions and the identification of metastasis from a breast primary.

[Differential diagnosis of spindle cell tumors of the breast from biopsy material]

Spindle cell proliferations are a rare but diagnostically challenging finding in breast biopsy material. The spectrum of possible diagnoses ranges from benign lesions, such as hamartomas, myofibroblastomas and biphasic tumors, such as adenomyoepitheliomas to malignant lesions, such as metaplastic carcinomas, phyllodes tumors and genuine sarcomas. A correct diagnosis from the preoperative biopsy material helps prevent inappropriate therapy and overtreatment or undertreatment. In this review five morphological patterns of spindle cell tumors of the breast and the most important representatives in this group are discussed.

Near-complete pathological response with preoperative chemotherapy in a patient with metaplastic breast carcinoma

Metaplastic breast carcinoma (MBC) is a rare form of breast cancer comprising less than 1% of all invasive breast carcinomas. There are no clinical studies available for the management of this rare disease and MBC is associated with a poor prognosis. We present a case of a 50-year-old female patient with MBC who showed a favorable response with preoperative chemotherapy. The patient presented with a palpable left breast mass, and diagnostic breast imaging showed a 4.4 cm mass in the left breast, which was biopsied. Pathological review led to a diagnosis of MBC. Staging workup for distant metastasis was negative. She received four cycles of dose-dense AC (doxorubicin and cyclophosphamide), followed by 10 weekly doses of carboplatin (area under the curve=2) and paclitaxel (80 mg/m). The patient underwent partial mastectomy and sentinel lymph node sampling, and pathological review indicated a near-complete pathological response, with few scattered malignant cells at the tumor bed. A current review of the literature on MBC is summarized in this report.

Pathways to breast cancer recurrence

Breast cancer remains a deadly disease, even with all the recent technological advancements. Early intervention has made an impact, but an overwhelmingly large number of breast cancer patients still live under the fear of “recurrent” disease. Breast cancer recurrence is clinically a huge problem and one that is largely not well understood. Over the years, a number of factors have been studied with an overarching aim of being able to prognose recurrent disease. This paper attempts to provide an overview of our current knowledge of breast cancer recurrence and its associated challenges. Through a survey of the literature on cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), various signaling pathways such as Notch/Wnt/hedgehog, and microRNAs (miRNAs), we also examine the hypotheses that are currently under investigation for the prevention of breast cancer recurrence.

A case of metaplastic breast cancer in a man

Metaplastic breast cancers (MPBCs) represent <1% of breast cancers. Reports of MPBC in men are limited to case reports. We report a case of MPBC with pulmonary metastasis occurring in a 59-year-old man who initially presented with a presumed breast abscess. Histology from the breast lesion revealed a poorly differentiated carcinoma and a computed tomography scan showed an ulcerative right-sided breast mass and an area of scarring in the apex of the left lung. The breast lesion and the lung lesion were resected separately and the histology from the lung showed a poorly differentiated carcinoma with sarcomatous features in keeping with metastasis from a primary breast cancer. Our patient then proceeded to chemotherapy with FEC 100 regimen (5-fluorouracil, epirubicin and cyclophosphamide). MPBC is an aggressive breast cancer that has a propensity to metastasis to the lungs. Prognosis is poor.

Molecular alterations in metaplastic breast carcinoma

Metaplastic carcinoma of the breast is a rare and heterogeneous subtype of breast carcinoma with a generally poor outcome, and few therapeutic options once disease recurs or progresses. Metaplastic carcinomas of the breast are usually of a larger size at diagnosis, with less frequent nodal metastasis compared with invasive ductal carcinoma no special type, and lack hormone and HER2 receptor expression. Recent research has revealed some potentially actionable genetic changes in a subset of these rare tumours. However, ongoing efforts to further characterise the genetic basis and the molecular alterations underlying the distinctive morphological and clinical characteristics of these tumours are needed in order to identify new targets for treatment. This review will describe the theories of pathogenesis of metaplastic breast carcinoma, and highlight genetic changes and potential therapeutic targets in this generally poor prognosis malignancy.