Phenotypic Alterations in Myoepithelial Cells Associated With Benign Sclerosing Lesions of the Breast

Radial Sclerosing Lesion (Radial Scar): Radiologic-Pathologic Correlation

Radial sclerosing lesions (RS, also referred to as "radial scars") and complex sclerosing lesions (CSL) are uncommon breast lesions often grouped together as a single entity in practice. RS/CSL have an incidence of <0.1% to 1% at core needle biopsy (CNB). When detected on CNB, imaging and pathology features must be carefully evaluated to determine appropriate surgical management or imaging follow-up due to potential for malignant upgrade at surgery. Detection of RS/CSL has increased with the advent of tomosynthesis, in which an RS/CSL is typically detected as architectural distortion with or without associated mass with spiculated margins. On US, an RS/CSL is most often occult or manifests as subtle distortion with adjacent cysts. Imaging findings cannot distinguish benign RS/CSL from those upgraded to malignancy at surgery, although larger lesion size may be associated with higher upgrade rates. Histologically, an RS has a central fibroelastotic nidus with entrapped-appearing ducts and proliferative changes at the periphery appearing to radiate from the center; CSL are larger than RS, more disorganized, and typically include multiple patterns of epithelial proliferations, including sclerosing adenosis, sclerosing papillomas, usual ductal hyperplasia, and cysts. RS/CSL with associated atypia at CNB have a 16%to 29% rate of upgrade to malignancy on surgical excision, thus rendering surgical excision essential. Conversely, an RS/CSL without associated atypia, particularly when ≤1 cm in size, has <3% rate of upgrade to malignancy at surgery, allowing consideration of imaging follow-up in lieu of excision. Here, we review recent literature as well as radiology and pathology findings of RS/CSL.

Nonneoplastic and neoplastic sclerosing lesions of the breast

Sclerosing lesions of the breast encompass a spectrum of benign and malignant entities and often pose a diagnostic challenge. Awareness of key morphologic features and pitfalls in the assessment of morphology and immunophenotype is essential to avoid over- or underdiagnosis and ensure optimal clinical management. This review summarizes nonneoplastic sclerosing lesions such as radial scar/complex sclerosing lesion, sclerosing adenosis, sclerosing intraductal papilloma, sclerosing variants of ductal adenoma and nipple adenoma, and fibroadenoma with extensive sclerosis, including their clinical presentation, characteristic morphology, differential diagnostic considerations, appropriate immunohistochemical work-up, when needed, and the clinical significance. In addition, atypical or neoplastic entities (such as atypical ductal hyperplasia, ductal carcinoma in situ, low-grade adenosquamous carcinoma, and fibromatosis-like metaplastic carcinoma) that can involve these sclerosing lesions are also briefly discussed.

Altered cytokeratin 5 expression in breast lobular myoepithelial cells

AIMS

Cytokeratin 5 (CK5) is a surrogate maker of progenitor cells and early glandular and myoepithelial cells (MECs) in the breast, and CK5 expression in breast MECs varies from ducts to lobules, and from normal to diseased tissue. However, the mechanisms underlying immunophenotypic alterations of CK5 expression in MECs remain unclear.

METHODS

CK5 expression in MECs of 20 normal breast samples, 58 ductal carcinoma in situ (DCIS; including 21 DCIS with extensive lobular involvement), 11 atypical ductal hyperplasia (ADH), 18 non-invasive lobular neoplasia consisting of 11 atypical lobular hyperplasia (ALH) and 7 lobular carcinoma in situ (LCIS), 20 cystic lobules and 10 usual ductal hyperplasia (UDH) involving lobules were observed to evaluate the effects of contact with benign hyperplastic or cancerous luminal cells and pressure of dilated glands on CK5 expression.

RESULTS

CK5 expression in normal ductal MECs was exclusively positive, whereas most normal lobular MECs were negative. In DCIS, cancerous ducts were primarily surrounded by CK5-positive MECs (91.0%), as were lobular acini involved by DCIS (89.2%), while the remaining normal acini maintained CK5-negative. CK5-positive MECs were found in 57.5% of acini in ALH and were more prevalent in LCIS (70.7%). CK5 expression was occasionally positive in both cystic lobules (16.7%) and lobules involved by UDH (14.3%), while an increase of CK5-positive MECs was found in ADH (38.2%).

CONCLUSIONS

These results suggest that CK5 expression in lobular MECs may be altered by contact with cancerous luminal cells rather than benign hyperplastic luminal cells or pressure from dilated glands.

Growth of a Nipple Adenoma After Estrogen Replacement Therapy

A nipple adenoma is an epithelial tumor of the lactiferous ducts, typically affecting women aged 50-60 years old. This case report discusses a 52-year-old woman who developed a papillary adenoma of the right nipple after initiating oral estrogen replacement therapy (ERT) for perimenopausal symptoms. A 4 mm punch biopsy and subsequent immunohistochemistry stain revealed the proliferation of ductal structures consistent with a papillary adenoma and tumor cells expressing estrogen receptors (ER) and progesterone receptors (PR). Despite their benign nature, nipple adenomas may exhibit alterations in immunophenotype, including ER and PR expression, which could lead to potential tumor growth in women undergoing these treatments. This case describes the first reported growth of a nipple adenoma in the context of estrogen replacement therapy, highlighting a potential risk of hormone therapy in promoting hyperproliferation of benign tumors such as nipple adenomas. When utilizing ERT, it is important to weigh the potential advantages and risks, as its application in the management of vasomotor symptoms during menopause may increase the risk of both breast cancer and benign proliferative breast diseases. These considerations underscore the need for individualized therapy when approaching perimenopausal and postmenopausal care.

Immunohistochemistry in the Diagnosis and Classification of Breast Tumors

CONTEXT.—

In the clinical practice of breast pathology, immunohistochemistry (IHC) of different markers is widely used for the diagnosis and classification of breast lesions.

OBJECTIVE.—

To provide an overview of currently used and recently identified IHC stains that have been implemented in the field of diagnostic breast pathology.

DATA SOURCES.—

Data were obtained from literature review and clinical experience of the authors as breast pathologists.

CONCLUSIONS.—

In the current review, we summarize the common uses of IHC stains for diagnosing different types of breast lesions, especially invasive and noninvasive breast lesions, and benign and malignant spindle cell lesions. In addition, the cutting-edge knowledge of diagnostic carcinoma markers will lead us to further understand the different types of breast carcinoma and differentiate breast carcinomas from other carcinomas of similar morphology. Knowing the strengths and limitations of these markers is essential to the clinical practice of breast pathology.

Adenosquamous proliferation in radial sclerosing lesions: Histologic spectrum and key features in systematic review of 247 lesions

Adenosquamous proliferation (ASP) is known to occur in the central nidus of radial sclerosing lesions (RSL) of the breast. However, their significance is debated and remains largely unknown. In addition, there is a histologic overlap between ASP and low-grade adenosquamous carcinomas (LGASC). We conducted a large retrospective review of 247 RSLs to evaluate the prevalence of ASP and quantitatively analyze associated histologic features of RSLs including size, stromal cellularity, and presence of chronic inflammation. The central nidus of RSLs were classified as hyalinized in 121 cases (49%), cellular in 37 cases (15%), and equally mixed hyalinized and cellular in 89 (36%). ASP occurred in 92 of 247 RSLs (37.2%). Cases with ASP were significantly associated with a cellular stroma; 78.4% of RSLS with cellular stroma had ASP versus just 11.6% of hyalinized RSLs. In our large cohort, inflammation is commonly found in RSLs with ASP (p= <0.001). In conclusion, we confirm that ASP is statistically more likely to be found in RSLs with a cellular stroma. In addition, ASP is commonly associated with chronic inflammation. The finding challenges the notion that prominent lymphocytes are a diagnostic clue to LGASC on limited biopsy material.

Imaging and Management of Radial Scars and Complex Sclerosing Lesions

Radial scars and complex sclerosing lesions, often collectively referred to as radial sclerosing lesions (RSLs), are breast lesions characterized by sclerotic stroma with entrapped epithelial elements. RSLs have imaging features that overlap with those of breast malignancy and often become the target of imaging-guided biopsy given their suspicious imaging appearance. These can be identified in isolation or can also be associated with atypia or other high-risk lesions that have intrinsic malignant potential, increasing the risk of carcinoma and affecting prognosis and management of RSLs. Because of this, management of these lesions remains controversial. Traditional management has been surgical excisional biopsy. However, as more RSLs are identified (because digital breast tomosynthesis allows identification of more architectural distortions), optimal management is evolving. Physicians in some practices are using a multidisciplinary approach to the management of RSLs when deciding on surgical excision of these lesions versus imaging follow-up. These discussions also incorporate individual patient risk factors and greater patient informed medical decision making. Reported upgrade rates of RSLs at core needle biopsy vary and can depend on the sampling method, number of samples, gauge of the needle, target being sampled, and radiologic-pathologic concordance or discordance. A precise sampling technique also allows greater accuracy of diagnosis and lower upgrade rates for these lesions, with radiologic-pathologic correlation as an integral component for further management decisions. The authors review the overall histopathologic, clinical, and imaging features of RSLs and discuss appropriate management based on currently available data regarding upgrade rates. ©RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.

Diagnostic Pitfalls in Breast Cancer Pathology With an Emphasis on Core Needle Biopsy Specimens

CONTEXT.—

Breast pathology has many mimics and diagnostic pitfalls. Evaluation of malignant breast lesions, particularly in the biopsy setting, can be especially challenging, with diagnostic errors having significant management implications.

OBJECTIVE.—

To discuss the pitfalls encountered when evaluating ductal carcinoma in situ and invasive breast carcinomas, providing histologic clues and guidance for appropriate use and interpretation of immunohistochemistry to aid in the correct diagnosis.

DATA SOURCES.—

Data were obtained from review of pertinent literature of ductal carcinoma in situ and invasive breast carcinomas and from the experience of the authors as practicing breast pathologists.

CONCLUSIONS.—

Awareness of the pitfalls in diagnosing breast cancers is important when creating a differential diagnosis for each breast lesion evaluated. This review will cover some of these scenarios to aid in the diagnostic process.

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.

Pitfalls in breast pathology

Accurate pathological diagnosis is the cornerstone of optimal clinical management for patients with breast disease. As non-operative diagnosis has now become the standard of care, histopathologists encounter the daily challenge of making definitive diagnoses on limited breast core needle biopsy (CNB) material. CNB samples are carefully evaluated using microscopic examination of haematoxylin and eosin (H&E)-stained slides and supportive immunohistochemistry (IHC), providing the necessary information to inform the next steps in the patient care pathway. Some entities may be difficult to distinguish on small tissue samples, and if there is uncertainty a diagnostic excision biopsy should be recommended. This review discusses (1) benign breast lesions that may mimic malignancy, (2) malignant conditions that may be misinterpreted as benign, (3) malignant conditions that may be incorrectly diagnosed as primary breast carcinoma, and (4) some IHC pitfalls. The aim of the review is to raise awareness of potential pitfalls in the interpretation of breast lesions that may lead to underdiagnosis, overdiagnosis, or incorrect classification of malignancy with potential adverse outcomes for individual patients.

Quality Issues in Diagnostic Immunohistochemistry in Breast Pathology

Immunohistochemistry techniques have been incorporated into surgical pathology for nearly a half-century and have since become intimately intertwined with its practice. In the realm of breast pathology, immunohistochemistry serves several purposes, including providing crucial prognostic and predictive data. Among its other applications, assessment of stromal invasion and establishment of mammary origin are crucial from a diagnostic standpoint. In these regards, sole reliance on immunohistochemistry may lead to misdiagnosis. In this review, we highlight pitfalls of immunohistochemistry commonly encountered in the practice of breast pathology and emphasize the importance of careful histopathological evaluation.

A deep learning model for breast ductal carcinoma in situ classification in whole slide images

The pathological differential diagnosis between breast ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) is of pivotal importance for determining optimum cancer treatment(s) and clinical outcomes. Since conventional diagnosis by pathologists using microscopes is limited in terms of human resources, it is necessary to develop new techniques that can rapidly and accurately diagnose large numbers of histopathological specimens. Computational pathology tools which can assist pathologists in detecting and classifying DCIS and IDC from whole slide images (WSIs) would be of great benefit for routine pathological diagnosis. In this paper, we trained deep learning models capable of classifying biopsy and surgical histopathological WSIs into DCIS, IDC, and benign. We evaluated the models on two independent test sets (n= 1382, n= 548), achieving ROC areas under the curves (AUCs) up to 0.960 and 0.977 for DCIS and IDC, respectively.

Papillary Breast Tumors: Continuing Controversies and Commentary on WHO's 2019 Criteria and Classification

The category of papillary breast tumors includes a limited number of entities. Nonetheless, this relatively uncommon group of tumors seems to instigate a disproportionate degree of diagnostic disquiet. As a group, papillary breast tumors suffer from a relatively high rate of discordant interpretation. The latter is due to the inherent complexity of the lesions compounded by conflicting criteria as well as simmering controversies. For instance, "encapsulated" papillary carcinoma remains contentious with regards to whether these are noninvasive or not, and the assessment of the extent of the invasive versus noninvasive components in many solid papillary carcinomas can be problematic. The latest classification system of breast tumors enunciated by the World Health Organization (WHO), that is, Breast Tumors, which appeared in 2019, mainly sought to incorporate advances in basic and clinical sciences into diagnostic criteria for the entire spectrum of breast neoplasms-including papillary ones. The latter category of tumors is discussed at some length in Breast Tumors; however, it still appears to suffer from some lack of clarity in its subclassification. It is our intent in this communication to provide an overview of the controversies around papillary breast tumors, and offer comments on its coverage in Breast Tumors-so that any tangible or perceived ambiguities therein could be addressed in its next edition.

Precision pathology as applied to breast core needle biopsy evaluation: implications for management

With the shift to de-escalation of therapy for some breast cancers and fewer surgical excisions for high-risk lesions identified on breast imaging studies at one end of the spectrum, and the greater use of neoadjuvant systemic therapy at the other end, pathologists are ever more critical in guiding management decisions for women with breast disease following core needle biopsy. One important consequence of this shift in management paradigms is the elimination of the opportunity for a "second-look" with the excision specimen to confirm or refine the diagnosis rendered on core needle biopsy. Thus, not only is there the imperative for accuracy and precision of core needle biopsy diagnoses, increasingly it is the only opportunity for that diagnosis.

Is it ductal carcinoma in situ with microinvasion or "Ductogenesis"? The role of myoepithelial cell markers

Mammary myoepithelial cells have been under-recognized for many years since they were considered less important in breast cancer tumorigenesis compared to luminal epithelial cells. However, in recent years with advances in genomics, cell biology, and research in breast cancer microenvironment, more emphasis has been placed on better understanding of the role that myoepithelial cells play in breast cancer progression. As the result, it has been recognized that the presence or absence of myoepithelial cells play a critical role in the assessment of tumor invasion in diagnostic breast pathology. In addition, advances in screening mammography and breast imaging has resulted in increased detection of ductal carcinoma in situ and consequently more diagnosis of ductal carcinoma in situ with microinvasion. In the present review, we discuss the characteristics of myoepithelial cells, their genomic markers and their role in the accurate diagnosis of ductal carcinoma in situ with microinvasion. We also share our experience with reporting of various morphologic features of ductal carcinoma in situ that may mimic microinvasion and introduce the term of ductogenesis.

Pitfalls and controversies in pathology impacting breast cancer management

Introduction: Breast cancer is a heterogeneous disease, at morphological, molecular, and clinical levels and this has significant implications for the diagnosis and management of the disease. The introduction of breast screening, and the use of small tissue sampling for diagnosis, the recognition of new morphological and molecular subtypes, and the increasing use of neoadjuvant therapies have created challenges in pathological diagnosis and classification.Areas covered: Areas of potential difficulty include columnar cell lesions, particularly flat epithelial atypia, atypical ductal hyperplasia, lobular neoplasia and its variants, and a range of papillary lesions. Fibroepithelial, sclerosing, mucinous, and apocrine lesions are also considered. Established and newer prognostic and predictive markers, such as immune infiltrates, PD-1 and PD-L1 and gene expression assays are evaluated. The unique challenges of pathology assessment post-neoadjuvant systemic therapy are also explored.Expert opinion: Controversies in clinical management arise due to incomplete and sometimes conflicting data on clinicopathological associations, prognosis, and outcome. The review will address some of these challenges.

Core needle biopsy of benign, borderline and in-situ problematic lesions of the breast: Diagnosis, differential diagnosis and immunohistochemistry

Core needle biopsy (CNB) is the most common sampling technique for the histologic evaluation of breast abnormalities. Diagnosing benign proliferative, borderline and some in-situ lesions in CNB is challenging and subject to a significant degree of interobserver variability. In addition, due to the inherent limitations of CNB, "upgrading" to a more significant pathology at excision is an important consideration for some lesions. Pathologists carry a major responsibility in patient diagnosis, risk stratification and management. Familiarity with the histologic features and the clinical significance of these common and problematic lesions encountered in CNB is necessary for adequate treatment and patient follow-up. This review will focus on benign, atypical and in-situ epithelial proliferations, papillary lesions, radial sclerosing lesions, adenosis and cellular fibroepithelial lesions. Highlights of histologic features, useful strategies for accurate diagnosis, basic immunohistochemistry and management will be presented.

Differences in immunohistochemistry utilization by general and breast subspecialty pathologists at a large academic institution

OBJECTIVES

Immunohistochemistry (IHC) can be a useful adjunct in diagnostic breast pathology, but best practices have not been clearly established. We sought to compare the patterns of p63 utilization between general pathologists (GP) and subspecialized breast pathologists (BP), analyze diagnostic discrepancy rates, and identify types of lesions requiring immunohistochemistry.

METHODS

The pathology database was searched over 6-year period to identify breast needle core biopsy cases utilizing p63 and subsequent excision results.

RESULTS

P63 was ordered more frequently by BP (2.3% of cores) compared to GP (1.1% of cores, p = 0.0005). The most frequent utilization of p63 by GP for benign lesions (44.0%) followed by invasive carcinomas (36.0%) while BP most frequently ordered p63 on invasive carcinomas (49.5%) and DCIS (26.6%).

CONCLUSIONS

While IHC use may be thought to be most helpful to those with less experience or knowledge in breast pathology, these results suggest that utilization is increased with subspecialty training.

Diagnosis of Papillary Breast Lesions on Core Needle Biopsy: Upgrade Rates and Interobserver Variability

The histologic distinction between papillary breast lesions remains challenging, especially with core biopsy (CB) specimens. A retrospective review of the clinical, imaging, and histologic findings was performed for patients with papillary breast lesions on CB from 2013 to 2017. The interpretation accuracy was expressed as upgrade rate relative to the excision diagnosis. Diagnostic reproducibility with and without immunohistochemistry was analyzed as interobserver variability among 3 board-certified pathologists. Among 57 papillary lesions with biopsies and excisions available for review, the upgrade rates were 0% for benign papilloma, 30% for papilloma with atypical ductal hyperplasia, and 25% for papilloma with ductal carcinoma in situ, resulting in an overall upgrade rate of 11.1%. There were no statistical differences between patients in an upgrade group and others, when comparing the patient age, clinical presentation, BI-RADS (Breast Imaging Reporting and Database System) category, location, and histologic grade. The overall interobserver variability of the 60 consecutive core biopsies of papillary breast lesions by morphology alone was in the "substantial" agreement range (κ = 0.79, 86% agreement), with an excellent κ score of 0.88 for papilloma (92% agreement). "Substantial" and "fair" κ values were seen for papilloma with atypical ductal hyperplasia/ductal carcinoma in situ (0.74, 84% agreement) and invasive carcinoma (0.40, 60% agreement). Use of immunohistochemical stains improved the κ values into "excellent" range (0.92, 94% agreement). Our study favors a conservative approach in the management of benign papillomas, at least in cases of good radiologic-pathologic concordance. Papillary breast lesions with atypia/malignancy show lower diagnostic reproducibility on CB, and utility of immunohistochemistry is recommended in challenging cases.

Core Needle Biopsy of the Breast: An Evaluation of Contemporary Data

Benign and atypical lesions associated with breast cancer risk are often encountered in core needle biopsies (CNBs) of the breast. For these lesions, the rate of "upgrade" to carcinoma in excision specimens varies widely in the literature. Many CNB studies are limited by a lack of radiological-pathological correlation, consistent criteria for excision, and clinical follow-up for patients who forego excision. This article highlights contemporary diagnostic criteria and outcome data that would support an evidence-based approach to the management of these nonmalignant lesions of the breast diagnosed on CNB.

Nuclear inverse polarity papillary lesions lacking myoepithelial cells: A report of two cases

Here, cases of a 68- (Case 1) and a 44-year-old (Case 2) female are presented. They had an abnormality in the breast, and came to our hospital for further examination and treatment. Radiologically, malignancy could not completely excluded so breast excision was performed. Histologically, both cases revealed papillary neoplastic lesions lined by fibrovascular core and nuclear inverse polarity without atypia. Loss of myoepithelial cells was observed by HE, p63, and calponin. Previous report indicate CK5/6, ER, p63 and MUC3 are important for distinguishing between papillary lesions according to the differential index (based on Allred score) of ([ER total score] + [MUC3 total score])/([CK5/6 total score] + [p63 total score] + 1). Based on this analysis, our two cases had benign lesions. However, based on immunopositivity for cell-cycle marker Cyclin-D1, Case 1 was negative, and Case 2 was about 70% positive. Additionally, the Ki-67 index was <1% in both cases, and no evidence of disease was observed after a maximum 62 months of follow-up in both cases, despite lack of additional treatment. Thus, we propose that lack of myoepithelial cells in papillary lesions do not necessarily indicate malignancy and are thought to be, at the most, uncertain malignant potential.

P40 Immunostain Does Not Outperform p63 as a Myoepithelial Cell Marker in the Daily Practice of Breast Pathology

P40 antibody has been shown to be a more specific squamous and basal cell marker compared with p63. As detection of myoepithelial cells (MECs) plays a critical role in breast pathology, and the fact that p40 targets an isoform of p63, this study was designed to compare these antibodies in a variety of lesions, especially those with an sclerotic stroma and carcinoma in situ. All studied lesions were selected from the daily cases of the 3 authors and stained with p63, p40, and calponin immunohistochemical stains. Thirty-four cases (and 19 internal controls) were included. Seventy percent constituted sclerotic lesions (12 cases) and ductal carcinoma in situ (12 cases). P40 and p63 stained all lesions and showed a similar patchy staining pattern in 50% of ductal carcinoma in situ and sclerotic lesions. Compared with internal controls, p40 and p63 demonstrated decreased staining intensity in up to 70% and 8% of all cases, respectively, with no cross-reactivity with mesenchymal cells and minor cross-reactivity with epithelial cells. In our study, p40 did not outperform p63 as a MEC marker. p40 showed a decreased intensity in a higher number of cases (P<0.0001). In our opinion, p63 continues to be the best nuclear marker for the detection of MECs in the daily practice of breast pathology.

Benign breast lesions that mimic malignancy

Many benign and reactive lesions of the breast show morphological overlap with malignant lesions. These benign mimics of malignancy often present diagnostic challenges to even the most experienced pathologists. This review focuses on several benign lesions of the breast that mimic malignant entities. For each of these lesions, we describe the key morphological and immunohistochemical features, potential diagnostic pitfalls, and our approach to arriving at the correct diagnosis.

Subareolar Sclerosing Ductal Hyperplasia

Subareolar sclerosing duct hyperplasia (SSDH) remains to be fully characterized nearly 20 years after initial description. Thirty-five SSDH cases diagnosed over a 16-year period (January 2000 to December 2015) were reviewed. All patients were female (mean age = 59 years, range = 18-80) who had presented with a unilateral solitary lesion (left 22, right 13) with a mean size of 1.3 cm (range = 0.4-3.0 cm), and showed florid and papillary epithelial hyperplasia with dense sclerosis without involvement of nipple or areolar epidermis. Significant lesions concurrent within SSDH included low-grade adenosquamous carcinoma (n = 1), ductal carcinoma in situ (DCIS; n = 1), lobular carcinoma in situ (LCIS; n = 1), and atypical ductal hyperplasia (ADH; n = 13). No case of SSDH recurred in a mean follow-up of 44 months (range = 6-189). Subsequent significant lesions occurred in 6 patients: DCIS (n = 3; ipsilateral 2, contralateral 1), ipsilateral ADH (n = 2), and ipsilateral atypical lobular hyperplasia (n = 1). Long-term follow-up for patients with SSDH is indicated as DCIS can occur subsequently in either breast.

Myoepithelial cells in lobular carcinoma in situ: distribution and immunophenotype

Myoepithelial cells have important physical and paracrine roles in breast tissue development, maintenance, and tumor suppression. Recent molecular and immunohistochemical studies have demonstrated phenotypic alterations in ductal carcinoma in situ-associated myoepithelial cells. Although the relationship of lobular carcinoma in situ (LCIS) and myoepithelial cells was described in 1980, further characterization of LCIS-associated myoepithelial cells is lacking. We stained 27 breast specimens harboring abundant LCIS with antibodies to smooth muscle myosin heavy chain, smooth muscle actin, and calponin. Dual stains for E-cadherin/smooth muscle myosin heavy chain and CK7/p63 were also performed. In each case, the intensity and distribution of staining in LCIS-associated myoepithelial cells were compared with normal breast tissue on the same slide. In 78% of the cases, LCIS-associated myoepithelial cells demonstrated decreased staining intensity for one or more myoepithelial markers. The normal localization of myoepithelial cells (flat against the basement membrane, pattern N) was seen in 96% of LCIS, yet 85% of cases had areas with myoepithelial cell cytoplasm oriented perpendicular to the basement membrane (pattern P), and in 30% of cases, myoepithelial cells appeared focally admixed with LCIS cells (pattern C). This study characterizes detailed architectural and immunophenotypic alterations of LCIS-associated myoepithelial cells. The finding of variably diminished staining favors application of several myoepithelial immunostains in clinical practice. The interaction of LCIS with myoepithelial cells, especially in light of the perpendicular and central architectural arrangements, deserves further mechanistic investigation.

A Comparative Study of Immunohistochemical Myoepithelial Cell Markers in Cutaneous Benign Cystic Apocrine Lesions

The use of immunohistochemical markers for myoepithelial cells (MEC) is a useful tool in the distinction of benign from malignant epithelial neoplasms. Although their use in breast tumors is well recognized, little is known concerning its application in comparable cutaneous lesions. Using benign cutaneous cystic apocrine lesions as a study model, the aim of this study was to compare 5 immunohistochemical markers [calponin, p63, smooth muscle actin (SMA), cytokeratin 14, and CD10] in their effectiveness to highlight MEC. Cases of apocrine hidrocystoma and cystadenoma (n = 44) were reviewed with a particular emphasis on proliferative features and apocrine change. The MEC staining pattern and the intensity and distribution scores in proliferative (n = 29) and nonproliferative (n = 15) lesions were assessed, and the differences between the 2 groups were statistically analyzed using Fisher exact test. Calponin and SMA stained MEC in the most consistent manner. Being a nuclear stain, p63 was easy to interpret but typically showed discontinuous staining. Cytokeratin 14 not only effectively highlighted MEC but also stained some luminal epithelial cells in an unpredictable manner. Because of prominent background dermal fibroblast staining, CD10 was often difficult to interpret. Only SMA and p63 showed a statistically significant difference in MEC staining intensity scores between the proliferative and nonproliferative groups. Our results show that immunohistological staining for MEC in benign cystic apocrine lesions of the skin is variable. The authors recommend that a panel of markers that includes calponin and p63 be used and highlight the need for awareness of specific caveats associated with individual markers.

Radial scars diagnosed on breast core biopsy: Frequency of atypia and carcinoma on excision and implications for management

AIMS

The risk of finding carcinoma in excisions following a core needle biopsy diagnosis of radial scar is not well defined and clinical management is variable. The aim of this study is to determine the frequency of high-risk lesions, ductal carcinoma in situ, and invasive carcinoma in excisions following a core biopsy diagnosis of radial scar.

METHODS AND RESULTS

Dedicated breast pathologists and radiologists correlated the histologic and radiologic findings and categorized radial scars as the target lesion or an incidental finding. High-risk lesions were defined as atypical hyperplasia or classical lobular carcinoma in situ. Of the 79 radial scars identified over a 14-year period, 22 were associated with atypia or carcinoma in the core biopsy. Thirty-seven (37) of the 57 benign radial scars underwent excision with benign findings in 30 (81%), high-risk lesions in six (16%), and flat epithelial atypia in one (3%). There were no upgrades to carcinoma. One patient with a benign radial scar developed a 3-mm focus of intermediate-grade estrogen receptor-positive ductal carcinoma in situ in the same quadrant of the ipsilateral breast 72 months after excision. One patient with an incidental un-excised benign radial scar was diagnosed with ductal carcinoma in situ at a separate site of suspicious calcifications.

CONCLUSIONS

In this series, none of the benign radial scars was upgraded to carcinoma. Radial scar was the targeted lesion in all cases with high-risk lesions on excision. Surgical excision may not be mandatory for patients with benign incidental radial scars on core biopsy.

Use of Immunohistochemical Stains in Epithelial Lesions of the Breast

BACKGROUND

During the last few decades, immunohistochemistry (IHC) has become an integral part of pathology. Although hematoxylin and eosin (H & E) stain remains the fundamental basis for diagnostic pathology of the breast, IHC stains provide useful and sometimes vital information. Moreover, considering the role of hormonal therapy in hormone receptor-positive breast tumors, as well as the availability of targeted chemotherapeutic agents for HER2-positive cases, IHC studies represent a major part of workups.

METHODS

A literature search was performed to explore the uses of IHC stains related to the diagnoses of breast lesions and prognostic/predictive information.

RESULTS

Selective use of IHC stains in conjunction with H & E examination helps resolve most diagnostic issues encountered by surgical pathologists during their day-to-day practice. Pathologists should be familiar with the use of each immunostain and its limitations to avoid interpretative errors.

CONCLUSIONS

IHC stains help guide the differential diagnosis of challenging epithelial lesions of the breast. They should be selectively and judiciously used and their findings must be interpreted with the differential diagnoses in mind and with an understanding of possible pitfalls.

Infiltrating epitheliosis of the breast: characterization of histological features, immunophenotype and genomic profile

AIMS

Infiltrating epitheliosis is a rare complex sclerosing lesion (CSL) of the breast, characterized by infiltrating ducts immersed in a scleroelastotic stroma and filled with cells having architectural and cytological patterns reminiscent of those of usual ductal hyperplasia. In this study we sought to define the molecular characteristics of infiltrating epitheliosis.

METHODS AND RESULTS

Eight infiltrating epitheliosis, adjacent breast lesions (one usual ductal hyperplasia, one papilloma, one micropapillary ductal carcinoma in situ and one low-grade adenosquamous carcinoma), and corresponding normal breast tissue from each case were microdissected and subjected to massively parallel sequencing analysis targeting all coding regions of 254 genes mutated recurrently in breast cancer and/or related to DNA repair. Mutations in components of the PI3K pathway were found in all infiltrating epitheliosis samples, seven of which harboured PIK3CA hotspot mutations, while the remaining case displayed a PIK3R1 somatic mutation.

CONCLUSIONS

Somatic mutations affecting PI3K pathway genes were found to be highly prevalent in infiltrating epitheliosis, suggesting that these lesions may be neoplastic rather than hyperplastic. The landscape of somatic genetic alterations found in infiltrating epitheliosis is similar to that of radial scars/CSLs, suggesting that infiltrating epitheliosis may represent one end of this spectrum of lesions.

CD10 Immunohistochemical Expression in Apocrine Lesions of the Breast

OBJECTIVE

In the breast, CD10 is expressed by myoepithelial cells (MECs), and apocrine metaplasia has also been mentioned as being positive with this marker. Apocrine lesions have been explored for the expression of CD10.

METHODS

The apocrine lesions studied included 11 cysts, 6 cases of apocrine adenosis, 2 of apocrine metaplasia or hyperplasia in papilloma, 13 ductal carcinomas in situ (DCIS) and invasive carcinomas (14 ductal and 4 lobular).

RESULTS

Benign apocrine lesions showed complete or partial luminal CD10 staining, although most cases included parts without staining, and 2 lesions were completely negative. The MECs were often but not always positive. Nine of the 13 cases of apocrine DCIS displayed no luminal staining, but 4 demonstrated very focal luminal positivity. The MECs around the DCIS showed a spectrum of staining from nil to strong and complete. Only 4 invasive carcinomas demonstrated luminal/membranous staining. Cytoplasmic CD10 positivity was seen focally in 4 invasive cancers and in 3 DCIS.

CONCLUSION

CD10 positivity is luminal/membranous in most benign apocrine lesions, the staining being nonuniversal and sometimes focal. Analogous staining in apocrine malignancies seems rarer in DCIS and even rarer in invasive apocrine carcinomas, but atypical cytoplasmic positivity may also occur. CD10 is not an ideal myoepithelial marker in apocrine lesions.

Basal cytokeratin phenotypes of myoepithelial cells indicates the origin of ductal carcinomas in situ of the breast

Terminal duct lobular unit (TDLU) is widely accepted as the origin of ductal carcinoma in situ of breast. The differentiation states of myoepithelial cells of breast ductal system hint the development of breast hyperplastic lesions. Basal cytokeratin (CK) phenotypes indicate the differentiation of myoepithelial cells. Using antibodies of CK5/6, CK14, and CK17, this study reports the basal CK phenotypes of myoepithelial cells in 20 foci of normal breast, 20 usual ductal hyperplasias, 36 ductal carcinomas in situ (DCIS), and 28 sclerosing adenosis (SA). The results showed that the positive staining of basal CKs of myoepithelial cells in normal ducts were significantly higher than those in normal lobules. The basal CK expression of myoepithelial cells of DCIS and usual ductal hyperplasia was similar to that of normal duct, whereas that of SA was similar to that of normal lobule. We propose a modified model of TDLU origin of intraductal carcinoma that most of DCIS originate from terminal ducts of TDLU, whereas most SA originate from lobules.

Adenosquamous proliferation of the breast and low grade adenosquamous carcinoma: a common precursor of an uncommon cancer?

Low grade adenosquamous carcinoma (LGASC) is rare but commonly reported to arise in association with benign proliferative and sclerosing breast lesions which themselves may show associated sclerosing or 'adenosquamous proliferation' (ASP) resembling LGASC, but are often derided as reactive mimics or attributed to earlier biopsy. Among other benign lesions, radial sclerosing lesion (RSL) may be associated with LGASC, yet attention is typically focused on its relationship to more common forms of mammary carcinoma. This study aimed to assess the presence and extent of ASP in the context of RSL in a small cohort of 20 cases and its similarity to LGASC.Twenty consecutive breast excisions that had a principal or incidental diagnosis of RSL were reviewed. RSLs that displayed foci of ASP were further examined with immunohistochemical markers for p63, calponin, cytokeratin 5/6, oestrogen and progesterone receptors.Sixty percent of excisions contained ASP either associated with a RSL or a concurrent papilloma, which morphologically and immunohistochemically were indistinguishable from the neoplastic ducts of LGASC. RSL with and without ASP broadly corresponded to accepted definitions for 'early' and 'late' lesions, respectively. ASP corresponded to the characteristic compact branching ducts of the core or nidus of a RSL.The morphological and immunophenotypic similarity of the ASP found in RSL and papillomata to LGASC warrants serious consideration that they are a potential precursor to LGASC, which may most commonly involute given the rarity of clinically apparent LGASC. Further study including micro-dissection of foci of ASP to compare its molecular genetic profile to that of LGASC is required.

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.

Utility of immunohistochemical markers in irradiated breast tissue: an analysis of the role of myoepithelial markers, p53, and Ki-67

Radiation therapy is an important adjunct to breast-conserving surgery, but the diagnosis of recurrent/de novo carcinoma in a background of radiation atypia can be difficult, especially on small biopsies. Immunostaining for myoepithelial cell proteins is often used to assess invasion in nonirradiated breast tissue, yet these stains have not been investigated specifically in irradiated breast. We studied 29 irradiated breast resection specimens, some with carcinoma in situ (CIS, n=13) and/or invasive carcinoma (n=13). Representative blocks were stained for the myoepithelial proteins p63, smooth muscle myosin heavy chain (SMM), calponin, CK5/6, the proliferative marker Ki-67, and the tumor-suppressor p53. Nonirradiated control tissue was also stained with Ki-67 and p53 (CIS, normal, contralateral). Areas of radiation atypia/atrophy and nearly all CIS in irradiated breast tissue had abundant myoepithelial cells as evidenced by SMM, calponin, and p63 stains, with focal staining attenuation or gaps with SMM and calponin and frequently absent CK5/6 staining. As predicted, myoepithelial cell staining was absent in invasive carcinoma. p63 staining revealed postradiation myoepithelial nuclear morphologic changes. p53 staining was increased, although weak, in irradiated non-neoplastic breast (12% irradiated; 4% nonirradiated); however, irradiated CIS had less p53 staining when compared with control CIS (3% irradiated; 38% nonirradiated). As expected, Ki-67 was increased in carcinoma as compared with non-neoplastic irradiated tissue. Thus, myoepithelial immunostaining is a useful diagnostic adjunct in irradiated breast, with caveats similar to nonirradiated breast. Ki-67 may be helpful in some postradiation specimens; however, p53 staining is not reliable in this setting.

Diagnostic role of immunohistochemistry in the evaluation of breast pathology specimens

CONTEXT

Immunohistochemistry plays a vital role in the evaluation of breast pathology specimens.

OBJECTIVE

To discuss the role of myoepithelial cell markers in the evaluation of various breast lesions. Other markers, such as E-cadherin and those used to differentiate mammary carcinoma from metastatic tumors to the breast, and markers used in the differential diagnosis of Paget disease, are also discussed.

DATA SOURCES

Data were obtained from review of the pertinent peer-reviewed literature.

CONCLUSIONS

Myoepithelial cell markers vary in their sensitivity and specificity, and one should be aware of the potential pitfalls in interpretation. Using panels of 2 or more myoepithelial cell markers is always recommended, either singly or in cocktail forms. Although negative E-cadherin staining supports the diagnosis of lobular origin, positive staining does not rule it out. Immunohistochemistry can be helpful in differentiating Paget disease from its mimics. Although metastatic tumors to the breast are rare, a triple-negative immunophenotype and absence of an in situ component should be a "red flag" for such possibility, especially in patients with clinical history of an extramammary malignancy.

Myoepithelial and epithelial-myoepithelial, mesenchymal and fibroepithelial breast lesions: updates from the WHO Classification of Tumours of the Breast 2012

In the 4th edition of the WHO Classification of Tumours of the Breast, myoepithelial lesions are retitled myoepithelial and epithelial-myoepithelial lesions in order to better reflect the dual participation of luminal and myoepithelial compartments in some key entities. Malignant myoepithelioma, described as a section within the chapter on myoepithelial lesions in the 3rd edition, is recognised in the 4th edition as part of metaplastic carcinoma. Adenomyoepithelioma with malignancy is categorised in terms of the cellular component undergoing malignant transformation. The list of antibodies that can be used for identifying myoepithelial cells is updated. Among mesenchymal lesions, new additions are nodular fasciitis and atypical vascular lesions, while the haemangiopericytoma is removed. The 3rd edition stated that pathological prediction of behaviour of phyllodes tumours is difficult in the individual case. In the 4th edition, some progress has been made in prioritisation and weighting of histological parameters that can potentially estimate probability of recurrence. The WHO Working Group advocates leaning towards a diagnosis of fibroadenoma in cases where there is histological uncertainty in distinction from a benign phyllodes tumour, or adopting the neutral term 'benign fibroepithelial neoplasm', as the clinical behaviour of fibroadenoma overlaps with that of benign phyllodes tumour. The 3rd edition terminology of 'periductal stromal sarcoma' is revised to 'periductal stromal tumour', akin to the widespread consensus to avoid the use of the term 'cystosarcoma' in the context of phyllodes tumours.

Use of immunohistochemistry in the diagnosis of problematic breast lesions

Most diagnoses in breast pathology can be made with H&E sections. Nevertheless immunohistochemistry plays a useful supplementary role. This article reviews the common uses of immunohistochemistry in diagnostic breast pathology. It is important to be aware of the limitations of individual antibodies. Such problems can often be overcome by using panels of antibodies. Quality control is also essential: internal and external controls should show appropriate staining. Immunohistochemistry must be interpreted in combination with the morphology seen on H&E sections. Myoepithelial markers, such as smooth muscle actin, smooth muscle myosin heavy chain and p63, are useful for distinguishing invasive carcinoma from sclerosing lesions and ductal carcinoma in situ (DCIS), and in the classification of papillary lesions. Basal cytokeratins can help distinguish epithelial hyperplasia of usual type (UEH) and clonal proliferations such as DCIS and lobular carcinoma in situ (LCIS). UEH usually shows patchy expression whereas DCIS and other clonal proliferations are typically negative. E-cadherin can usually separate DCIS and LCIS: DCIS typically shows membrane staining and most LCIS is negative. Cytokeratins can be used to detect small nodal metastases or subtle invasive carcinomas such as invasive lobular carcinomas. Immunohistochemistry plays a useful role in diagnosing spindle cell lesions such as a panel of cytokeratins to identify spindle cell carcinomas. Immunohistochemistry is helpful in recognising metastases to the breast. Different antibodies are useful for different tumours: WT1 for ovarian carcinoma; TTF1 for pulmonary adenocarcinoma; S100, melan-A and HMB45 for melanoma; and lymphoid markers for lymphoma.

Benign apocrine papillary lesions of the breast lacking or virtually lacking myoepithelial cells-potential pitfalls in diagnosing malignancy

Two cases of apocrine papillary lesions are presented, in which myoepithelial cells were not visualized on hematoxylin and eosin-stained slides. A complex sclerosing papillary lesion did not exhibit myoepithelial cells on p63 and CD10 immunostaining, although a thin rim of myoepithelial cell cytoplasm was revealed by smooth muscle actin, calponin, and S100 immunostains. In the other lesion, without sclerosis, myoepithelium was not detected in the central papillary cores or at the periphery of the cystic wall on hematoxylin and eosin-stained sections or with any of the myoepithelial markers tested, although two small wall areas did display the presence of myoepithelium. These two cases strengthen the view that the lack of myoepithelium alone in apocrine lesions cannot be equated with malignancy. As recent literature reports have demonstrated that myoepithelial cells may be missing from benign apocrine changes and proliferations of different types, a reconsideration of the diagnostic criteria of the malignancy of such lesions appears essential.

Best practices in diagnostic immunohistochemistry: myoepithelial markers in breast pathology

CONTEXT

Numerous immunohistochemical stains have been shown to exhibit exclusive or preferential positivity in breast myoepithelial cells relative to their luminal/epithelial counterparts. These myoepithelial markers provide invaluable assistance in accurately classifying breast proliferations, especially in core biopsies. Although numerous myoepithelial markers are available, they differ in their sensitivity, specificity, and ease of interpretation, which may be attributed, to a large extent, to the variable immunoreactivity of these markers in stromal cells including myofibroblasts, vessels, luminal/epithelial cells, and tumor cells.

OBJECTIVE

To review commonly used myoepithelial markers in breast pathology and a selection of diagnostic scenarios where they may be useful.

DATA SOURCES

The information outlined in this review article is based on our experiences with routine cases and a review of English-language articles published between 1987 and 2008.

CONCLUSIONS

To demonstrate the presence or absence of myoepithelial cells, a panel-based approach of 2 or more markers is recommended. Markers that most effectively combine sensitivity, specificity, and ease of interpretation include smooth muscle myosin heavy chains, calponin, p75, p63, P-cadherin, basal cytokeratins, maspin, and CD10. These markers, however, display varying cross-reactivity patterns and variably reduced expression in the myoepithelial cells bordering in situ carcinomas. The choice of a myoepithelial marker should be dependent on a combination of factors, including published evidence on its diagnostic utility, its availability, performance characteristics that have been achieved in a given laboratory, and the specific diagnostic scenario. When its use is deemed necessary, immunohistochemistry for myoepithelial cells in breast pathology is most effective when conceptualized as supplemental, rather than central to routine morphologic interpretation.

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

This review describes the classification, clinical presentation, pathological features and clinical behaviour of adenomyoepithelioma (AME) of the breast. It is based on an extensive review of the literature and study of a collection of cases built up over a 17-year period at the British Columbia Cancer Agency. The diversity of the morphology encountered in both benign and malignant AME is described. The behaviour of malignant AME seems to be related to the grade of the malignant component.