Adenomyoepithelioma of the breast: a review stressing its propensity for malignant transformation

The "Forgotten" Subtypes of Breast Carcinoma: A Systematic Review of Selected Histological Variants Not Included or Not Recognized as Distinct Entities in the Current World Health Organization Classification of Breast Tumors

Breast carcinoma is the most common cancer in women. Nineteen different subtypes of breast carcinomas are recognized in the current WHO classification of breast tumors. Except for these subtypes, there are a number of carcinomas with special morphologic and immunohistochemical features that are not included in the 5th WHO classification, while others are considered special morphologic patterns of invasive breast carcinoma of no special type. In this manuscript, we systematically review the literature on four different subtypes of invasive breast carcinoma, namely lymphoepithelioma-like breast carcinoma, breast carcinoma with osteoclast-like giant cells, signet-ring breast carcinoma, and metaplastic breast carcinoma with melanocytic differentiation. We describe their clinicopathological characteristics, focusing on the differential diagnosis, treatment, and prognosis.

Benign Adenomyoepithelioma of the Breast: A Case Report

Adenomyoepitheliomas of the breast are rare tumors that are characterized histologically as having both epithelial and myoepithelial components. While adenomyoepitheliomas are considered benign lesions, existing literature supports their potential for malignant transformation. These tumors also exhibit nonspecific and variable findings on noninvasive imaging, posing additional challenges in management. We present a rare case of an adenomyoepithelioma diagnosed in a 65-year-old female who was treated with surgical resection of her tumor, with histopathology negative for malignant transformation. By describing this patient's management course, we aim to contribute to existing literature analyzing adenomyoepitheliomas and help guide future treatment.

Human basal-like breast cancer is represented by one of the two mammary tumor subtypes in dogs

BACKGROUND

About 20% of breast cancers in humans are basal-like, a subtype that is often triple-negative and difficult to treat. An effective translational model for basal-like breast cancer is currently lacking and urgently needed. To determine whether spontaneous mammary tumors in pet dogs could meet this need, we subtyped canine mammary tumors and evaluated the dog-human molecular homology at the subtype level.

METHODS

We subtyped 236 canine mammary tumors from 3 studies by applying various subtyping strategies on their RNA-seq data. We then performed PAM50 classification with canine tumors alone, as well as with canine tumors combined with human breast tumors. We identified feature genes for human BLBC and luminal A subtypes via machine learning and used these genes to repeat canine-alone and cross-species tumor classifications. We investigated differential gene expression, signature gene set enrichment, expression association, mutational landscape, and other features for dog-human subtype comparison.

RESULTS

Our independent genome-wide subtyping consistently identified two molecularly distinct subtypes among the canine tumors. One subtype is mostly basal-like and clusters with human BLBC in cross-species PAM50 and feature gene classifications, while the other subtype does not cluster with any human breast cancer subtype. Furthermore, the canine basal-like subtype recaptures key molecular features (e.g., cell cycle gene upregulation, TP53 mutation) and gene expression patterns that characterize human BLBC. It is enriched in histological subtypes that match human breast cancer, unlike the other canine subtype. However, about 33% of canine basal-like tumors are estrogen receptor negative (ER-) and progesterone receptor positive (PR+), which is rare in human breast cancer. Further analysis reveals that these ER-PR+ canine tumors harbor additional basal-like features, including upregulation of genes of interferon-γ response and of the Wnt-pluripotency pathway. Interestingly, we observed an association of PGR expression with gene silencing in all canine tumors and with the expression of T cell exhaustion markers (e.g., PDCD1) in ER-PR+ canine tumors.

CONCLUSIONS

We identify a canine mammary tumor subtype that molecularly resembles human BLBC overall and thus could serve as a vital translational model of this devastating breast cancer subtype. Our study also sheds light on the dog-human difference in the mammary tumor histology and the hormonal cycle.

Human basal-like breast cancer is represented by one of the two mammary tumor subtypes in dogs

Background

About 20% of breast cancers in humans are basal-like, a subtype that is often triple negative and difficult to treat. An effective translational model for basal-like breast cancer (BLBC) is currently lacking and urgently needed. To determine if spontaneous mammary tumors in pet dogs could meet this need, we subtyped canine mammary tumors and evaluated the dog-human molecular homology at the subtype level.

Methods

We subtyped 236 canine mammary tumors from 3 studies by applying various subtyping strategies on their RNA-seq data. We then performed PAM50 classification with canine tumors alone, as well as with canine tumors combined with human breast tumors. We investigated differential gene expression, signature gene set enrichment, expression association, mutational landscape, and other features for dog-human subtype comparison.

Results

Our independent genome-wide subtyping consistently identified two molecularly distinct subtypes among the canine tumors. One subtype is mostly basal-like and clusters with human BLBC in cross-species PAM50 classification, while the other subtype does not cluster with any human breast cancer subtype. Furthermore, the canine basal-like subtype recaptures key molecular features (e.g., cell cycle gene upregulation, TP53 mutation) and gene expression patterns that characterize human BLBC. It is enriched histological subtypes that match human breast cancer, unlike the other canine subtype. However, about 33% of canine basal-like tumors are estrogen receptor negative (ER-) and progesterone receptor positive (PR+), which is rare in human breast cancer. Further analysis reveals that these ER-PR+ canine tumors harbor additional basal-like features, including upregulation of genes of interferon-γ response and of the Wnt-pluripotency pathway. Interestingly, we observed an association of PGR expression with gene silencing in all canine tumors, and with the expression of T cell exhaustion markers (e.g., PDCD1 ) in ER-PR+ canine tumors.

Conclusions

We identify a canine mammary tumor subtype that molecularly resembles human BLBC overall, and thus could serve as a vital spontaneous animal model of this devastating breast cancer subtype. Our study also sheds light on the dog-human difference in the mammary tumor histology and the hormonal cycle.

Malignant Adenomyoepithelial Tumour of the Breast - a Rare Diagnosis - Case Report

Breast adenomyoepithelioma is an unusual tumour characterized by a biphasic proliferation of epithelial and myoepithelial cells. Most of the breast adenomyoepitheliomas are considered to be benign and characterized by propensity for local recurrence. Malignant change can occur rarely in one or both cellular components. We here present a case of a 70-year-old previously healthy female who initially presented with a painless breast lump. The patient underwent wide local excision in view of suspicion of malignancy and sent for frozen section regarding the diagnosis and margins which surprisingly came as adenomyoepithelioma. Final histopathology came as low-grade malignant adenomyoepithelioma. The patient shows no sign of tumour recurrence in the follow up.

Breast lesions with myoepithelial phenotype

Myoepithelial cells (MECs) constitute a continuous layer of cells surrounding the breast glands, localised between the epithelial cells (ECs) and the basal membrane. MECs play important roles in normal mammary gland as they produce basal membrane and stimulate secretion. During neoplastic transformation, MECs act as a barrier preventing stromal invasion. MECs themselves can undergo a great variety of changes, ranging from hyperplastic to metaplastic, to neoplastic, and giving rise to a wide spectrum of morphological pictures sometimes difficult to interpret on routine diagnoses. Several benign and malignant breast tumours can present features of MECs differentiation. As these latter tumours are quite infrequent, the purpose of the present study is to offer a review of the morphological spectrum of MECs lesions, with correlations to prognosis.

Case report and literature review: Malignant adenomyoepithelioma after breast augmentation

Background

Breast malignant adenomyoepithelioma (MAME) after breast augmentation has never been reported.

Case summary

We reported a case of a 55-year-old woman who was diagnosed with breast MAME 16 years after breast augmentation. Breast augmentation was performed on the patient with two 200 ml round textured prostheses in the subpectoral plane through axillary incisions in 2004. However, a breast ultrasound in 2020 revealed a suspicious malignant lump in the right breast, which was finally confirmed as MAME by pathology. Skin-sparing modified radical mastectomy and immediate breast reconstruction with expander implantation were performed. Subsequently, the patient received three cycles of chemotherapy with the regimen of anthracycline and cyclophosphamide. In the following nearly 2 years of follow-up, no tumor recurrence and metastasis were found, and the overall treatment was satisfactory for the patient.

Conclusion

Here, we present a unique case in which a patient was diagnosed with breast MAME after breast augmentation. Skin-sparing modified radical mastectomy and immediate breast reconstruction with expander implantation are feasible approaches that yield at least short-term oncological safety and acceptable aesthetic results. However, whether there is a potential relationship between MAME and breast implants remains to be further explored. Meanwhile, due to the rarity of breast MAME, more authoritative strategies considering both oncological safety and aesthetics to seek better long-term therapeutic effects are needed.

Adenomyoepithelioma of the breast with unusual confounding diagnostic feature: a case report

Background

Adenomyoepithelioma of the breast is an uncommon subtype of breast neoplasm that occurs in adults over a wide age range but most commonly in middle-aged and older adults. It usually presents as a solitary palpable mass or is detected on breast radiographic images. Histologically, it is a biphasic tumor with proliferation of both the epithelial and myoepithelial components of the glands, with variable types of tissue metaplasia.

Case presentation

A 64-year-old Saudi woman who underwent regular breast screening (mammogram) presented to our hospital following radiographic detection of a suspicious grouped microcalcification in the upper outer quadrant of her right breast on the mammogram. A wide local excision of the right breast lump was performed. Following histopathological examination of the breast lump, the final diagnosis was breast adenomyoepithelioma with mucoepidermoid/divergent differentiation, with no evidence of malignancy. About two years after the operation, a clinical follow-up conducted outside our hospital showed the development of ductal carcinoma in situ in the same breast.

Conclusion

Although the prognosis and the plan of treatment remains the same, our case highlights the complexities in making an accurate diagnosis between the various types of metaplasia within adenomyoepithelioma on one hand and the presence of mucoepidermoid differentiation in adenomyoepithelioma on the other.

Insights into Immune Escape During Tumor Evolution and Response to Immunotherapy Using a Rat Model of Breast Cancer

Animal models are critical for the preclinical validation of cancer immunotherapies. Unfortunately, mouse breast cancer models do not faithfully reproduce the molecular subtypes and immune environment of the human disease. In particular, there are no good murine models of estrogen receptor-positive (ER+) breast cancer, the predominant subtype in patients. Here, we show that Nitroso-N-methylurea-induced mammary tumors in outbred Sprague-Dawley rats recapitulate the heterogeneity for mutational profiles, ER expression, and immune evasive mechanisms observed in human breast cancer. We demonstrate the utility of this model for preclinical studies by dissecting mechanisms of response to immunotherapy using combination TGFBR inhibition and PD-L1 blockade. Short-term treatment of early-stage tumors induced durable responses. Gene expression profiling and spatial mapping classified tumors as inflammatory and noninflammatory, and identified IFNγ, T-cell receptor (TCR), and B-cell receptor (BCR) signaling, CD74/MHC II, and epithelium-interacting CD8+ T cells as markers of response, whereas the complement system, M2 macrophage phenotype, and translation in mitochondria were associated with resistance. We found that the expression of CD74 correlated with leukocyte fraction and TCR diversity in human breast cancer. We identified a subset of rat ER+ tumors marked by expression of antigen-processing genes that had an active immune environment and responded to treatment. A gene signature characteristic of these tumors predicted disease-free survival in patients with ER+ Luminal A breast cancer and overall survival in patients with metastatic breast cancer receiving anti-PD-L1 therapy. We demonstrate the usefulness of this preclinical model for immunotherapy and suggest examination to expand immunotherapy to a subset of patients with ER+ disease. See related Spotlight by Roussos Torres, p. 672.

Breast adenomyoepithelioma from a radiologic perspective

Adenomyoepithelioma of the breast (AB) is an uncommon tumor that is characterized by the biphasic proliferation of epithelial and myoepithelial cells. The radiologic findings for AB have been scantly reported. This paper aims to analyze the characteristic findings for AB on ultrasonography (US) and mammography. This retrospective descriptive study used the Breast Imaging-Reporting and Data System (BI-RADS) to analyze the US and mammography findings for histologically confirmed AB in patients attended at our institution between 2007 and 2019. We identified a total of 13 AB in 13 women. All patients underwent US. On US, 12 lesions were seen as oval nodules, and the remaining lesion was irregular-shaped; 8 lesions had circumscribed margins, 3 had angled margins, and 2 had microlobulated margins. Regarding the echo pattern, 8 lesions were hypoechoic and 5 were complex (solid-cystic). On color Doppler, 11 lesions were vascularized nodules and 2 were avascular nodules. In conclusion, we present the imaging characteristics for a series of cases of AB. It is unlikely that this lesion can be suspected solely on the basis of the imaging findings; nevertheless, it is important for radiologists to be familiar with AB to carry out a good radiopathologic correlation.

Adenomyoepithelioma of the breast: a rare diagnosis complicated by surgical emergency and diagnostic uncertainty

A woman in her 80s was referred as an emergency case with a large oedematous and ulcerating lesion of the right breast. There was a 5-month history of increasing breast volume with new onset skin breakdown and discharge. Imaging revealed an extensive heterogeneous mass requiring drainage. No diagnosis was received from multiple biopsies and immediate surgical resection of the breast and axillary sampling was prioritised given the deteriorating patient condition. Postoperative histology identified a biphasic Adenomyoepithelioma of low malignant potential, a rare presentation compounding the complexity of management. The diagnostic uncertainty of this case highlighted the importance of MDT collaboration and the flexibility of current management pathways when dealing with cases requiring urgent surgical intervention. Axillary sampling in the context of unsuccessful preoperative biopsy represented a comprehensive means for assessing the need for further surgical or systemic management in the context of unconfirmed malignancy in a deteriorating patient.

Combination of Adenomyoepithelioma and Adenoid Cystic Carcinoma of the Breast: A Case Report of an Uncommon Histopathological Entity

BACKGROUND Adenomyoepithelioma and adenoid cystic carcinoma are uncommon types of breast tumors. Adenoid cystic carcinoma accounts for 0.1% of breast neoplasms and typically presents as a tender breast tumor, mostly in the subareolar area. Adenoid cystic carcinoma usually appears in women in the fifth or sixth decade of life and predominantly presents as a mixed tumor, with cribriform, tubular, and solid growth characteristics. Adenomyoepithelioma of the breast shows epithelial and smooth muscle characteristics. Adenomyoepithelioma rarely goes through malignant transformation and is an uncommon type of benign breast tumor. CASE REPORT Our study reviews the current published literature regarding the combination of these 2 rare neoplasms of the breast and shows a rare case of a 48-year-old woman with a combination of adenoid cystic carcinoma and adenomyoepithelioma. CONCLUSIONS The combination of adenoid cystic carcinoma and adenomyoepithelioma should be part of the differential diagnosis in breast cancer. More research is needed regarding the optimal therapy, which is currently surgical excision.

Diagnostic challenges of adenomyoepithelioma: A case report

INTRODUCTION

Breast adenomyoepithelioma is a very uncommon tumor, which is generally considered to be benign, however malignant transformation has been reported.

PRESENTATION OF CASE

We report two cases of two women with breast adenomyoepithelioma.

CONCLUSION

Diagnosis of adenomyoepithelioma is challenging because tumor may mimic other breast diseases. It has neither specific clinical signs nor radiological features, and the diagnosis is based on histopathological examination of the lesion. The treatment of choice is surgery. The type of surgery depends on the tumor factors and breast size. In malignant cases treatment such as radiotherapy, chemotherapy, immunotherapy may be used as well. It is very important to give an adequate treatment, otherwise the risk of tumor recurrence, growth or even metastatic spread, when tumor has malignant potential, increases.

Papillary lesions of the breast

Papillary lesions of the breast represent a heterogeneous group of lesions including benign papillomas, papillomas with focal epithelial atypia, fully fledged ductal carcinoma in situ (DCIS) or lobular neoplasia, papillary DCIS, encapsulated papillary carcinomas without or with invasion, solid papillary carcinomas, and invasive papillary carcinomas. A micropapillary pattern characterized by lack of fibrous stalks within the papillae is observed in micropapillary DCIS and invasive micropapillary carcinoma. In addition, a variety of other rare breast lesions reveals a papillary architecture such as tall cell carcinoma with reversed polarity (TCCRP) and mucinous cystadenocarcinoma, adenomyoepithelioma, and secretory carcinoma. In addition, benign lesions such as usual ductal hyperplasia, apocrine metaplasia, gynecomastia, and juvenile papillomatosis may show a papillary or micropapillary architecture. Fragments of a benign papilloma in a breast biopsy are considered a lesion of uncertain malignant potential (B3 in the European classification) and excision is mostly recommended. Although the knowledge about molecular pathology of papillary breast lesions has increased, there is not sufficient evidence for diagnostically useful molecular features, yet. The aim of this review is to provide an update on papillary and micropapillary lesions with emphasis on problematic areas for daily diagnostic work including biopsies.

Establishment and characterization of organoids from a patient with adenomyoepithelioma of the breast

Adenomyoepithelioma (AME) of the breast is a rare tumor that is composed of proliferating epithelial and myoepithelial cells. The pathogenesis of AME remains unclear, and no breast cancer cells have been identified in such tumor tissues. In this study, we established patient-derived breast cancer organoids from the surgical tumor samples of an elderly Chinese woman with an AME of the breast. Our findings confirmed the successful establishment of organoids from an AME of the breast of this patient. A short tandem repeat analysis revealed that the DNA signature of the AME of the breast organoids matched the DNA signature of the original tumor specimen. Moreover, diameter assay confirmed that the organoids from the breast AME showed sensitivity to paclitaxel and doxorubicin treatments, which was similar to, but lesser than that of primary culture cells. In conclusion, we established an efficient 3-dimensional breast cancer organoid culture platform from an AME of the breast. This platform can be effectively used for exploring clinicopathological and genomic characteristics of AME of the breast to identify possible treatments and increase awareness about this disease entity.

Malignant adenomyoepithelioma of the breast: Two case reports and review of the literature

BACKGROUND

Malignant adenomyoepithelioma (AME) of the breast is a rare tumor in which malignancy can arise from either epithelial or myoepithelial components, or from both cell types. The incidence and prognosis of malignant AME of the breast are difficult to assess due to its rarity. Therefore, the optimal treatment for this disease is still controversial.

CASE SUMMARY

We present two middle-aged women (48 and 56 years old) with malignant AME of the breast. Core needle biopsy was performed before surgery. However, breast adenoma and malignant tumors were observed. The preoperative diagnosis of malignant AME of the breast is still challenging for pathologists and clinicians. Both patients underwent mastectomy and sentinel lymph node biopsy, both of which were negative, followed by adjuvant chemotherapy.

CONCLUSION

The follow-up duration of the two patients was two years and four months, respectively. No signs of relapse or metastasis have been observed thus far.

Uncommon Tumors and Uncommon Presentations of Cancer in the Breast

Purpose of review

The purpose is to present a case series of rare diagnoses and unusual presentations of breast lesions with radiologic-pathologic correlation from a major cancer center, and to review the recent literature on each entity with a focus on radiology-pathology concordance. We present our findings and experience from cases of metastatic small cell lung carcinoma to the breast, IgG-4 related breast disease, breast implant associated anaplastic large cell lymphoma, granular cell tumor, pleomorphic sarcoma, adenomyoepithelioma, post-radiation angiosarcoma, and breast carcinoma after risk-reducing total mastectomy.

Recent findings

It is essential for physicians to have knowledge of rare breast diagnoses and unusual breast disease presentations to formulate a complete differential diagnosis, recognize radiological-pathological concordance of these entities and provide appropriate patient care.

Summary

Current literature on these rare described entities exists mainly as case reports, case series and small-scale studies. By sharing our findings, we hope to educate trainees in radiology, pathology and other fields across the continuum of care in radiologic-pathologic correlation, while also augmenting the existing literature on these rare entities.

HRAS is a therapeutic target in malignant chemo-resistant adenomyoepithelioma of the breast

Malignant adenomyoepithelioma (AME) of the breast is an exceptionally rare form of breast cancer, with a significant metastatic potential. Chemotherapy has been used in the management of advanced AME patients, however the majority of treatments are not effective. Recent studies report recurrent mutations in the HRAS Q61 hotspot in small series of AMEs, but there are no preclinical or clinical data showing H-Ras protein as a potential therapeutic target in malignant AMEs. We performed targeted sequencing of tumours’ samples from new series of 13 AMEs, including 9 benign and 4 malignant forms. Samples from the breast tumour and the matched axillary metastasis of one malignant HRAS mutated AME were engrafted and two patient-derived xenografts (PDX) were established that reproduced the typical AME morphology. The metastasis-derived PDX was treated in vivo by different chemotherapies and a combination of MEK and BRAF inhibitors (trametinib and dabrafenib). All malignant AMEs presented a recurrent mutation in the HRAS G13R or G12S hotspot. Mutation of PIK3CA were found in both benign and malignant AMEs, while AKT1 mutations were restricted to benign AMEs. Treatment of the PDX by the MEK inhibitor trametinib, resulted in a marked anti-tumor activity, in contrast to the BRAF inhibitor and the different chemotherapies that were ineffective. Overall, these findings further expand on the genetic features of AMEs and suggest that patients carrying advanced HRAS-mutated AMEs could potentially be treated with MEK inhibitors.

Triple-negative breast carcinomas of low malignant potential: review on diagnostic criteria and differential diagnoses

Triple-negative breast carcinomas constitute a wide spectrum of lesions, mostly being highly aggressive. Nevertheless, some special histologic subtypes can have low malignant potential. The purpose of the present paper is to review diagnostic criteria and prognostic parameters of breast neoplasms of special histotypes. Specifically, adenoid cystic carcinoma, adenomyoepithelioma, acinic cell carcinoma, mucoepidermoid carcinoma, tall cell carcinoma with reverse polarity, and secretory carcinoma will be discussed. For each tumour, definition and morphological and molecular features, together with prognostic parameters, will be presented. Paradigmatic cases will be illustrated.

Breast adenomyoepithelioma from a radiologic perspective

Adenomyoepithelioma of the breast (AB) is an uncommon tumor that is characterized by the biphasic proliferation of epithelial and myoepithelial cells. The radiologic findings for AB have been scantly reported. This paper aims to analyze the characteristic findings for AB on ultrasonography (US) and mammography. This retrospective descriptive study used the Breast Imaging-Reporting and Data System (BI-RADS) to analyze the US and mammography findings for histologically confirmed AB in patients attended at our institution between 2007 and 2019. We identified a total of 13 AB in 13 women. All patients underwent US. On US, 12 lesions were seen as oval nodules, and the remaining lesion was irregular-shaped; 8 lesions had circumscribed margins, 3 had angled margins, and 2 had microlobulated margins. Regarding the echo pattern, 8 lesions were hypoechoic and 5 were complex (solid-cystic). On color Doppler, 11 lesions were vascularized nodules and 2 were avascular nodules. In conclusion, we present the imaging characteristics for a series of cases of AB. It is unlikely that this lesion can be suspected solely on the basis of the imaging findings; nevertheless, it is important for radiologists to be familiar with AB to carry out a good radiopathologic correlation.

Updates on Lobular Neoplasms, Papillary, Adenomyoepithelial, and Fibroepithelial Lesions of the Breast

CONTEXT.—

This review article is a result of the breast pathology lectures given at the Sixth Chinese American Pathologists Association annual diagnostic pathology course in October 2020 (held virtually due to the coronavirus disease 2019).

OBJECTIVE.—

To update recent developments, in this review article, the authors wrote minireviews in the following 4 areas: lobular neoplasm, adenomyoepithelial lesions, papillary lesions, and fibroepithelial lesions.

DATA SOURCES.—

The sources include extensive literature review, personal research, and experience.

CONCLUSIONS.—

With the wide practice of screening mammography, these lesions are not uncommon in image-guided core biopsies and excisional specimens. Many recent developments have emerged in understanding these lesions. We aim to provide readers with concise updates for each of these lesions with a focus on recent updates in definitions, diagnostic criteria, management, and molecular profiles that are most relevant to the daily practice of pathology and patient management.

Adenomyoepithelioma of the breast: a proposal for classification

Breast lesions with a prominent myoepithelial cell component constitute a heterogeneous group of benign and malignant neoplastic proliferations. These lesions are often dual epithelial-myoepithelial, but may be purely myoepithelial cell in nature. Benign epithelial-myoepithelial lesions typically maintain the morphology and immunophenotype of the normal bilayer epithelial myoepithelial structures. However, the distinction between the two cell components is not always clear-cut in malignant lesions in which the histogenesis of myoepithelial cells remains uncertain. Neoplastic biphasic epithelial-myoepithelial lesions of the breast include adenomyoepithelioma (AME), pleomorphic adenoma and adenoid cystic carcinoma. Four histological patterns of classical AME have been described: tubular, lobulated, spindle-cell and adenosis variants. Overlapping patterns occur and some AMEs display an intraductal papillary pattern that may represent a fifth variant. AME can be benign or malignant. Classical AME may show atypical features, which are not sufficient for the diagnosis of malignancy (atypical AME). Atypical AME is recognised as a lesion of uncertain malignant potential with limited metastatic capability. Based on the histological features, we propose a classification of malignant AME (M-AME) into three variants: M-AME in situ, M-AME invasive and AME with invasive carcinoma. In this review, we provide an overview of myoepithelial lesions of the breast focusing on the classification of AME to improve not only the consistency of reporting but also help to guide further management decision-making.

Immunohistochemical assessment of HRAS Q61R mutations in breast adenomyoepitheliomas

AIMS

Breast adenomyoepitheliomas (AMEs) are uncommon tumours. Most oestrogen receptor (ER)-positive AMEs have mutations in phosphoinositide 3-kinase (PI3K) pathway genes, whereas ER-negative AMEs usually harbour concurrent mutations affecting the HRAS Q61 hotspot and PI3K pathway genes. Here, we sought to determine the sensitivity and specificity of RAS Q61R immunohistochemical (IHC) analysis for detection of HRAS Q61R mutations in AMEs.

METHODS AND RESULTS

Twenty-six AMEs (14 ER-positive; 12 ER-negative) previously subjected to massively parallel sequencing (n = 21) or Sanger sequencing (n = 5) of the HRAS Q61 hotspot locus were included in this study. All AMEs were subjected to IHC analysis with a monoclonal (SP174) RAS Q61R-specific antibody, in addition to detailed histopathological analysis. Nine ER-negative AMEs harboured HRAS mutations, including Q61R (n = 7) and Q61K (n = 2) mutations. Five of seven (71%) AMEs with HRAS Q61R mutations were immunohistochemically positive, whereas none of the AMEs lacking HRAS Q61R mutations (n = 17) were immunoreactive. RAS Q61R immunoreactivity was restricted to the myoepithelium in 80% (4/5) of cases, whereas one case showed immunoreactivity in both the epithelial component and the myoepithelial component. RAS Q61R immunohistochemically positive AMEs were associated with infiltrative borders (P < 0.001), necrosis (P < 0.01) and mitotic index in the epithelial (P < 0.05) and myoepithelial (P < 0.01) components. RAS Q61R IHC assessment did not reveal Q61K mutations (0/2).

CONCLUSIONS

IHC analysis of RAS Q61R shows high specificity (100%) and moderate sensitivity (71%) for detection of HRAS Q61R mutations in breast AMEs, and appears not to detect HRAS Q61K mutations. IHC analysis of RAS Q61R may constitute a useful technique in the diagnostic workup of ER-negative AMEs.

Adenomyoepithelioma with a human epidermal growth factor receptor 2-fluorescence in situ hybridization-confirmed ductal carcinoma in situ component: A case report and review of the literature

INTRODUCTION

Breast adenomyoepithelioma (AME) is a rare tumor composed of myoepithelial cells and ductal or luminal cells. Most cases of AME are benign, but rare cases in which either or both cell types exhibited malignant features have been reported. Due to its rarity, no diagnostic criteria for malignancy have been established for AME.

PATIENT CONCERNS

A 64-year-old woman presented with a mass in her right breast. Fine-needle aspiration cytology and biopsy examinations revealed lesions composed of spindle-shaped cells and round epithelial cells. AME was suspected, and partial mastectomy was performed.

DIAGNOSIS

The tumor specimen showed AME, which mainly consisted of spindle-shaped myoepithelial cells with slight atypia, admixed with tubular luminal cells and small areas of atypical intraductal proliferative lesions. No apparent features of malignancy, such as necrosis or invasion, were seen in the myoepithelial cells or the luminal or intraductal component. However, the atypical intraductal component exhibited focal nuclear atypia, a cribriform pattern, and moderate to strong membranous human epidermal growth factor receptor 2 (HER2) immunoreactivity. HER2 amplification was detected in focal regions of the atypical intraductal component by fluorescence in situ hybridization (FISH), which resulted in a diagnosis of AME with ductal carcinoma in situ.

OUTCOMES

The patient did not receive further therapy and was free from tumor recurrence at 23 months after the operation.

CONCLUSION

HER2 FISH might be useful for evaluating suspected AME tumors for malignancy when an atypical ductal lesion that lacks definitive features of malignancy is encountered.

Malignant adenomyoepithelioma of the breast: A case report

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Malignant breast adenomyoepithelioma (AME), rare subtype of cancer that usually benign.

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Mastectomy and sentinel lymph node biopsy with no further recurrence.

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Inner epithelial cells revealed positivity for CK5/6.

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Myoepithelial layers were positive for P63, CK5/6, SMA and S100 protein.

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Metastases chance of 30–40% with malignant adenomyoepithelioma, generally haematogenous route. Whereas metastases to the axillary lymph nodes is rare.

Introduction

Malignant breast adenomyoepithelioma (AME) is a rare subtype of breast cancer. AME is mostly a benign disease that uncommonly undergoes malignant transformation.

Presentation of case

Here we present a case of a young, previously healthy female who initially presented with a painless breast lump. The patient underwent wide local excision for atypical cells with squamous metaplasia by core biopsy, but final histopathology showed AME with carcinoma. Thus, a mastectomy and a sentinel lymph node biopsy was undertaken. The patient had an uneventful recovery and no recurrence after the second surgery.

Discussion and conclusion

Malignant transformation of adenomyoepithelioma is reported in a small number of cases. Benign AME may be treated with wide local excision as recurrence is rare locally. Whereas malignant AME tends to be treated with simple mastectomy with or without lymph node biopsy.

Genotype-phenotype associations in breast pathology: Achievements of the past quarter century

The first genotype-phenotype relationship in breast pathology developed in 1994 with the discovery of the CDH1 gene. This finding eventually provided biological insight into the characteristic morphology of invasive lobular carcinoma. Subsequent investigative efforts have uncovered additional molecular alterations largely responsible for the histology of several breast neoplasms including secretory carcinoma, adenoid cystic carcinoma, tall cell carcinoma with reversed polarity, fibroepithelial lesions, and most recently, adenomyoepithelioma. Evaluation of the genomic landscape of other special types of breast cancer with distinctive growth patterns, such as invasive mucinous carcinoma, have yet to uncover recurring cytogenetic and/or molecular alterations. Despite the lack of a hallmark alteration in mucinous carcinoma, it is important to note the relative decrease in PIK3CA mutations compared with invasive carcinoma of no special type. In this review, we describe the clinical and pathologic features of breast tumors with recognized genotype-phenotype correlations and summarize the molecular alterations of mucinous carcinoma.

Rapid Local Recurrence of Breast Myoepithelial Carcinoma Arising in Adenomyoepithelioma: A Case Report

Adenomyoepithelioma (AME) is a rare breast neoplasm composed of both epithelial and myoepithelial cells with biphasic proliferation. Although most AMEs are benign, malignant transformation of either or both cellular components may occur. This report describes an unusual rapid local tumor recurrence a month after excision of the myoepithelial carcinoma arising in an AME. Ultrasound and MRI showed small recurrent masses in the superficial part of a hematoma. This report suggests the benefit of immediate postoperative breast imaging in patients with malignant AME with potential for local recurrence, such as those with narrow resection margins or high mitotic activity.

Challenges in management of male breast adenomioepithelioma with malignant behavior: Case report

RATIONALE

Male adenomyoepithelioma of the breast with malignant features is a rare tumor with only one previous case reported in the literature over 25 years ago.

PATIENT CONCERNS

We report the case of a 63-year-old man admitted to our Oncology Institute with a painless tumor mass of 6 cm in the left breast with no additional regional lymph nodes. Ultrasound revealed a complex cystic tumor mass of 60 mm in the left breast, with both anechoic (cystic) and echogenic (solid) components, with ill-defined margin.

DIAGNOSES

Extemporaneous assessment showed a solid (invasive) papillary intracystic carcinoma. Definitive pathology examination revealed the presence of a breast malignant adenomyoepithelioma.

INTERVENTIONS

Based on the extemporaneous assessment, wide tumor excision was performed. The tumor board decided to continue treatment with adjuvant anthracycline-based chemotherapy.

OUTCOMES

After 6 years of follow-up, the patient is cancer-free. No chronic side effects were noted.

LESSONS

Because this pathology is extremely rare, no guidelines are available for its therapeutic approach. All decisions regarding patient management should be made by a multi-disciplinary team and can only be based on clinical experience and the few cases reported in female patients.

Recurrent hotspot mutations in HRAS Q61 and PI3K-AKT pathway genes as drivers of breast adenomyoepitheliomas

Adenomyoepithelioma of the breast is a rare tumor characterized by epithelial−myoepithelial differentiation, whose genetic underpinning is largely unknown. Here we show through whole-exome and targeted massively parallel sequencing analysis that whilst estrogen receptor (ER)-positive adenomyoepitheliomas display PIK3CA or AKT1 activating mutations, ER-negative adenomyoepitheliomas harbor highly recurrent codon Q61 HRAS hotspot mutations, which co-occur with PIK3CA or PIK3R1 mutations. In two- and three-dimensional cell culture models, forced expression of HRAS^Q61R in non-malignant ER-negative breast epithelial cells with or without a PIK3CA^H1047R somatic knock-in results in transformation and the acquisition of the cardinal features of adenomyoepitheliomas, including the expression of myoepithelial markers, a reduction in E-cadherin expression, and an increase in AKT signaling. Our results demonstrate that adenomyoepitheliomas are genetically heterogeneous, and qualify mutations in HRAS, a gene whose mutations are vanishingly rare in common-type breast cancers, as likely drivers of ER-negative adenomyoepitheliomas.

Adenomyoepithelioma is a rare tumor of the breast with an unknown genetic basis. Here the authors perform a genomic analysis of adenomyoepitheliomas revealing that their repertoire of somatic mutations vary according to the estrogen receptor (ER) status, and that ER-negative tumors harbor recurrent mutations in HRAS and PI3K pathway genes.

[Adenomyoepithelioma of the breast: Report of four cases and literature review]

Adenomyoepitheliomas of the breast are infrequent tumors with a variable histological appearance, and they can mimic several epithelial, myoepithelial and biphasic lesions of the breast. We have reviewed four cases of adenomyoepithelioma of the breast diagnosed between 2005 and 2015 in our institution (Hospital Clínico San Carlos). Mean age was 57years. All lesions were solid irregular masses located in the upper quadrants (3 of them in the right breast and one in the left), with an average size of 13mm. Microscopically 2 of them were tubular and the remaining 2 were lobulated subtypes. Hyaline, myxoid and cystic areas, peripheral pseudoinfiltration and satellite nodules were occasionally seen. Myoepithelial cells were fusiform and immunohistochemically they were actin, calponin, p63, S100 and CD10 positive and CKAE1-AE3 negative, with variable CK23BE12 and CK5/6 staining. In all cases lumpectomy was curative, no recurrences or malignant degeneration were observed.

The Spectrum of Triple-Negative Breast Disease: High- and Low-Grade Lesions

Triple-negative breast cancer is viewed clinically as an aggressive subgroup of breast cancer. In fact, most triple-negative breast cancers are poor-prognosis tumors with a complex genomic landscape. However, triple-negative disease is vastly heterogeneous, encompassing multiple entities with marked genetic, transcriptional, histologic, and clinical differences, with neoplasms in this group ranging from low to high grade. Among the less common low-grade triple-negative lesions, two large subgroups, both with a rather indolent behavior, can be distinguished: a low-grade triple-negative breast neoplasia family, which includes nonobligate precursors of triple-negative breast cancer, and, despite being low-grade, harbors the complex genomic landscape of usual triple-negative breast cancer, and the salivary gland-like tumors of the breast, lacking all the cardinal molecular features of conventional triple-negative breast cancer and underpinned by specific fusion genes or hotspot mutations, which may be of diagnostic and possibly therapeutic utility. Progression to high-grade triple-negative breast cancer likely occurs in both subgroups but at different rates. In this review, we describe the heterogeneity of triple-negative disease, focusing on the histologic and molecular features of the low-grade lesions. Recognition that triple-negative breast cancer is an operational term and that triple-negative disease is heterogeneous and includes low-grade forms driven by distinct sets of genetic alterations is germane to the successful implementation of precision medicine.

Radiotherapy in the Multidisciplinary Management of Adenomyoepithelioma of the Breast with an Axillary Lymph Node Metastasis: A Case Report and Review of the Literature

We describe a case of aggressive adenomyoepithelioma (AME) of the breast with a lymph node metastasis. A 63-year-old female presented with a fluctuating breast mass and clinically palpable lymph nodes. The patient underwent excisional biopsy followed by mastectomy with lymph node dissection and adjuvant radiotherapy (RT). Clinical behavior of both benign and malignant AME is described with the review of the literature and treatment recommendations.

Update on Immunohistochemical Analysis in Breast Lesions

CONTEXT

- The utility of immunohistochemistry (IHC) in breast lesions needs to be updated with exceptions among these lesions. Biomarker studies with IHC in triple-negative breast carcinoma may help develop targeted therapies for this aggressive breast cancer. The distinction of metastatic lung adenocarcinoma to the breast and invasive breast carcinoma has significant prognostic and therapeutic implications. The determination can be challenging because both primary tumors can express estrogen receptor and/or HER2 by IHC, creating a diagnostic dilemma.

OBJECTIVES

- To provide a practical update on the use of IHC markers in differential diagnoses in breast lesions, including benign, atypical, precancerous, and malignant tumors; to highlight recently published research findings on novel IHC markers in triple-negative breast carcinoma cases; and to reinforce the importance of IHC use as an ancillary tool in distinguishing metastatic lung adenocarcinoma to the breast from primary breast carcinoma using real case examples.

DATA SOURCES

- PubMed (US National Library of Medicine, Bethesda, Maryland) literature review and authors' research data and personal experiences were used in this review.

CONCLUSIONS

- Immunohistochemistry has an important role in making differential diagnoses in breast lesions in morphologically equivocal settings; recognizing IHC expression status in the exceptions among these lesions will aid in the correct diagnosis of challenging breast cases. Studies suggest that androgen receptor, p16, p53, GATA3, and PELP1 may have potential diagnostic, prognostic, and predictive value in triple-negative breast carcinoma cases; these findings may provide insight and a greater understanding of the tumor biology in triple-negative breast carcinomas. In distinguishing metastatic estrogen receptor-positive or HER2⁺ lung adenocarcinoma to the breast from primary breast carcinoma, napsin A, TTF-1, and GATA3 comprise a useful IHC panel.

Malignant Adenomyoepithelioma of the Breast and Responsiveness to Eribulin

Adenomyoepithelioma (AME) of the breast is an uncommon tumor characterized by its dual differentiation into luminal cells and myoepithelial cells. In most cases these tumors have a benign clinical course, but distant metastases have been reported. We present the case of a 51-year-old woman diagnosed with malignant AME. The patient underwent a right modified radical mastectomy, and pathological examination confirmed the diagnosis of malignant AME. Ten months after the operation, multiple hepatic, pleural, and abdominal wall metastases were detected. A number of palliative chemotherapeutic agents were tried, including anthracycline and taxanes. However, the disease continued to progress, and superior vena cava syndrome developed as a result of direct tumor invasion. The patient received salvage eribulin monotherapy. After two cycles of this treatment, her clinical symptoms were ameliorated, and a computed tomography scan showed a partial response. Eribulin chemotherapy was thus effective in treating malignant AME in this case.

[Adenomyoepithelioma with dominant myoepithelial contingent of the breast: A case report and literature review]

We report a case of adenomyoepithelioma with predominant myoepithelial quota, a rare tumor of the breast due to proliferation of epithelial and myoepithelial cells in a patient of 71 years. This lesion, with difficult radiological and pathological diagnosis (biopsy) in the initial stage of the treatment, should benefit from surgical resection in healthy margin. In fact, this tumor is evolving in most cases on a benin mode, but cases of local or metastatic recurrences were reported. Histological and immunohistochemical arguments are important to reach the final diagnosis.

Reactivation of multipotency by oncogenic PIK3CA induces breast tumour heterogeneity

Breast cancer is the most frequent cancer in women and consists of heterogeneous types of tumours that are classified into different histological and molecular subtypes. PIK3CA and P53 (also known as TP53) are the two most frequently mutated genes and are associated with different types of human breast cancers. The cellular origin and the mechanisms leading to PIK3CA-induced tumour heterogeneity remain unknown. Here we used a genetic approach in mice to define the cellular origin of Pik3ca-derived tumours and the impact of mutations in this gene on tumour heterogeneity. Surprisingly, oncogenic Pik3ca(H1047R) mutant expression at physiological levels in basal cells using keratin (K)5-CreER(T2) mice induced the formation of luminal oestrogen receptor (ER)-positive/progesterone receptor (PR)-positive tumours, while its expression in luminal cells using K8-CReER(T2) mice gave rise to luminal ER(+)PR(+) tumours or basal-like ER(-)PR(-) tumours. Concomitant deletion of p53 and expression of Pik3ca(H1047R) accelerated tumour development and induced more aggressive mammary tumours. Interestingly, expression of Pik3ca(H1047R) in unipotent basal cells gave rise to luminal-like cells, while its expression in unipotent luminal cells gave rise to basal-like cells before progressing into invasive tumours. Transcriptional profiling of cells that underwent cell fate transition upon Pik3ca(H1047R) expression in unipotent progenitors demonstrated a profound oncogene-induced reprogramming of these newly formed cells and identified gene signatures characteristic of the different cell fate switches that occur upon Pik3ca(H1047R) expression in basal and luminal cells, which correlated with the cell of origin, tumour type and different clinical outcomes. Altogether our study identifies the cellular origin of Pik3ca-induced tumours and reveals that oncogenic Pik3ca(H1047R) activates a multipotent genetic program in normally lineage-restricted populations at the early stage of tumour initiation, setting the stage for future intratumoural heterogeneity. These results have important implications for our understanding of the mechanisms controlling tumour heterogeneity and the development of new strategies to block PIK3CA breast cancer initiation.

Immunohistochemical expression of myoepithelial markers in adenomyoepithelioma of the breast: a unique paradoxical staining pattern of high-molecular weight cytokeratins

To determine which immunohistochemical markers are useful for the identification of neoplastic myoepithelial cells in adenomyoepithelioma of the breast, the expression of seven myoepithelial markers (α-smooth muscle actin (α-SMA), calponin, p63, CD10, cytokeratin 5/6, cytokeratin 14, and S-100) was examined in 19 lesions from 16 patients. The lesion consisted of seven spindle and 12 clear cell lesions. For normal myoepithelial cells, α-SMA, calponin, and p63 were significantly more sensitive than cytokeratin 5/6, cytokeratin 14, and S-100. There was no significant difference in the expression of α-SMA, calponin, p63, and CD10 in neoplastic myoepithelial cells of adenomyoepithelioma regardless of spindle or clear cell types. In spindle cell lesions, high-molecular weight cytokeratins (HMWCK; cytokeratin 5/6 and cytokeratin 14) tended to show higher staining scores and S-100 showed lower staining scores than other markers. In clear cell lesions, HMWCK showed significantly lower staining scores than the other five markers. There was no significant difference in staining scores among the other five markers. HMWCK showed a unique paradoxical staining pattern in clear cell lesions, with diffusely positive inner epithelial cells and completely negative outer myoepithelial cells. Although the sensitivity of HMWCK in clear cell lesions is low, with this unique paradoxical staining pattern and relatively high sensitivity in spindle cell lesions, HMWCK could be useful in diagnosing adenomyoepithelioma. In choosing immunohistochemical markers, any of the seven markers are useful, but combining HMWCK and any one of α-SMA, calponin, and p63 would be a good panel for the diagnosis of adenomyoepithelioma.