Adenomyoepitheliomas of the Breast Frequently Harbor Recurrent Hotspot Mutations in PIK3-AKT Pathway-related Genes and a Subset Show Genetic Similarity to Salivary Gland Epithelial-Myoepithelial Carcinoma

Salivary Gland-like Tumors of the Breast

CONTEXT

The World Health Organization classification of tumors of the breast recognizes several special type carcinomas and benign lesions with features comparable to those of salivary gland tumors.

OBJECTIVE

To discuss the histologic, immunophenotypic, molecular, and clinical features of salivary gland-like carcinomas of the breast. These breast tumors are often negative for hormone receptors and human epidermal growth factor receptor 2 (HER2), that is, triple-negative, but they generally have a much better prognosis than triple-negative breast carcinomas of no special type. We compare the immunophenotypic, molecular, and clinical features of these breast tumors with their salivary gland counterparts, highlighting similarities and differences. We also discuss benign salivary gland-like breast tumors. Finally, we highlight recent developments in understanding the molecular pathogenesis of these breast tumors and novel ancillary studies that can be used to support their diagnosis.

DATA SOURCES

A literature review was conducted, and papers were selected for further analysis and discussion by the authors of this review based on their novelty, applicability, and impact in the field.

CONCLUSIONS

Breast tumors that exhibit morphologic overlap with salivary gland tumors have been recognized by pathologists for decades, but the similarities and differences in their molecular pathogenesis have not been understood until more recently. These developments have led to novel diagnostic tools and further knowledge of these rare breast lesions.

Recurrent IDH2 Mutations in Salivary Gland Striated Duct Adenoma Define an Expanded Histologic Spectrum Distinct From Canalicular Adenoma

Striated duct adenoma (SDA) is a rare salivary gland neoplasm defined by histologic similarity to normal striated ducts. However, doubt persists about whether SDA represents a genuine entity distinct from canalicular adenoma and if a malignant counterpart exists. This study aims to evaluate the molecular underpinnings of SDA to clarify its pathogenesis and classification. We identified 10 SDA and 2 tumors called low-grade adenocarcinoma not otherwise specified that were retrospectively recognized to resemble SDA. All cases showed recurrent histologic features including (1) discrete monophasic tubules, (2) tall columnar eosinophilic cells, (3) monotonous oval nuclei, and (4) scant fibrous stroma, and most were positive for S100 protein (91%), SOX10 (80%), and CK7 (80%). Although 1 case was previously called adenocarcinoma based on interdigitation with normal acini, this pattern was also seen in some SDA, and likely does not indicate malignancy; the significance of growth surrounding nerve in 1 other case is less clear. Targeted sequencing identified IDH2 R172X mutations in all 8 cases with sufficient tissue, with positivity for IDH1/2 mutation-specific immunohistochemistry in 9 cases stained. In contrast, 5 canalicular adenomas lacked IDH2 mutations or other oncogenic alterations. Overall, IDH2 R172X mutations are a defining feature of SDA that, in combination with its recognizable pathologic profile, confirm it is a unique entity separate from canalicular adenoma. IDH1/2 mutation-specific immunohistochemistry may provide a convenient tool to facilitate diagnosis. Both morphology and IDH2 mutations raise parallels between SDA and breast tall cell carcinoma with reverse polarity.

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.

Primary mucoepidermoid carcinoma of the breast arising in adenomyoepithelioma

Mucoepidermoid carcinoma (MEC) and adenomyoepithelioma (AME) are uncommon neoplasms of the breast that are more commonly noted in the salivary glands. AMEs are benign tumours that are known to undergo malignant transformation. This report describes the first case of a MEC arising in AME in a woman in her 50s.

Papillary Neoplasms of the Breast: Diagnostic Features and Molecular Insights

Papillary neoplasms of the breast are a heterogeneous group of tumors characterized by fibrovascular cores lined by epithelium, with or without myoepithelial cells. Papillary neoplasms include benign, atypical, and malignant tumors that show varying histopathologic features and clinical outcomes. Appropriate pathologic classification is crucial to guide clinical treatment. Classification of papillary neoplasms is largely based on morphology, with immunohistochemistry playing an ancillary role to establish diagnoses. Recent molecular studies have provided insight into the genomics of these lesions. This review summarizes the histologic, immunohistochemical, and molecular features of papillary neoplasms of the breast that are important for diagnosis and treatment.

Pulmonary epithelial-myoepithelial carcinoma (P-EMC) with focal high grade transformation: Molecular and cytologic findings

BACKGROUND

Pulmonary epithelial-myoepithelial carcinoma (P-EMC) is a rare type of salivary gland tumor of the lung. Diagnosis from preoperative biopsies or fine needle aspiration (FNA) cytology specimens is difficult given the rarity of the tumor and overlapping cytomorphology with other entities. These tumors generally have a good prognosis, however prior reports of recurrence and metastasis to lymph nodes have been reported. Further, little is known about the malignant potential of high grade transformation. The molecular characteristics of this entity are unknown, with only a few case reports commenting on molecular findings. Here, we report a case of P-EMC with focal high grade transformation. We present its diagnostic pitfalls on cytology specimens, surgical pathology, immunohistochemistry, and molecular findings.

CASE PRESENTATION

A 72 year old female presented with an incidentally detected lung mass. A chest computed tomography (CT) demonstrated a left hilar mass measuring 4.1 cm with endobronchial extension into the left upper lobe. On the initial endobronchial core needle biopsy and cytology FNA, the tumor was misinterpreted as squamous cell carcinoma. The patient subsequently underwent a left pneumonectomy along with mediastinal lymph node dissection. Final surgical pathology of the resection specimen indicated a P-EMC with focal high grade transformation. The patient is disease-free 1 year post-surgery.

CONCLUSIONS

Due to the rarity of P-EMC, insufficient sampling and histologic heterogeneity, diagnosis of P-EMC on preoperative core needle biopsy or FNA specimen is difficult. Herein, we present a rare case of P-EMC, with a pre-operative FNA cytology specimen that consisted of tumor cells with dense cytoplasm and moderate cytologic atypia, strong positive staining pattern of p40, that was misdiagnosed as squamous cell carcinoma. Follow up surgical resection showed P-EMC with focal high grade transformation. Salivary gland EMCs with high grade transformation have previously been reported to have a worse prognosis, however, little is known about the malignant potential in the lung. Next generation sequencing (NGS) using a 397-gene solid tumor panel identified variants in DNMT3A, APC, STAT3 in both low and high grade components, while KDM5C was present only in the high grade transformation.

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.

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.

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.

The Diagnostic Utility of RAS Q61R Mutation-specific Immunohistochemistry in Epithelial-Myoepithelial Carcinoma

Epithelial-myoepithelial carcinoma (EMC) is a rare salivary gland cancer characterized by biphasic tubular structures composed of inner ductal and outer clear myoepithelial cells. Because of its histologic variety and overlap of histologic features with other salivary gland tumors, there are broad differential diagnoses. The HRAS Q61R mutation has been reported to be frequent in and specific to EMC. We evaluated the usefulness of RAS Q61R mutant-specific immunohistochemical (IHC) staining for detecting this genetic alteration in EMC. We investigated 83 EMC cases and 66 cases of salivary gland tumors with an EMC-like component, including pleomorphic adenoma, adenoid cystic carcinoma, basal cell adenoma/adenocarcinoma, and myoepithelial carcinoma. Sanger sequencing was performed for HRAS, KRAS, and NRAS. The diffuse and membranous/cytoplasmic RAS Q61R IHC expression was observed in 65% of EMC cases, in which all cases harbored the HRAS Q61R mutation. IHC-positive cases were present only in de novo EMCs (54/76 cases, 71%) but not in EMCs ex pleomorphic adenoma. The immunoreactivity was almost always restricted to the myoepithelial cells. Conversely, all EMC cases lacking the HRAS Q61R mutation were negative on IHC. In addition, only 3% of EMC-like tumors showed the abovementioned immunopositivity. None of the cases examined carried KRAS or NRAS mutations. IHC for RAS Q61R is highly sensitive and specific for detecting the HRAS Q61R mutation in EMC. Since significant immunopositivity was almost exclusively identified in nearly two thirds of EMCs but seldom in the histologic mimics, the IHC of RAS Q61R is a useful tool for diagnosing EMC in general pathology laboratories.

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.

Salivary Mucinous Adenocarcinoma Is a Histologically Diverse Single Entity With Recurrent AKT1 E17K Mutations: Clinicopathologic and Molecular Characterization With Proposal for a Unified Classification

Mucin-producing salivary adenocarcinomas were historically divided into separate colloid carcinoma, papillary cystadenocarcinoma, and signet ring cell carcinoma diagnoses based on histologic pattern, but have recently been grouped together in the adenocarcinoma not otherwise specified category. It is currently unclear if these tumors represent 1 or more distinct entities and how they are related to well-circumscribed papillary mucinous lesions with recurrent AKT1 E17K mutations that were recently described as salivary intraductal papillary mucinous neoplasm. Here, we sought to evaluate the clinicopathologic and molecular features of salivary mucinous adenocarcinomas to clarify their classification. We identified 17 invasive mucin-producing salivary adenocarcinomas, 10 with a single histologic pattern, and 7 with mixed patterns. While most tumors demonstrated papillary growth (n=15), it was frequently intermixed with colloid (n=6) and signet ring (n=3) architecture with obvious transitions between patterns. All were cytokeratin 7 positive (100%) and cytokeratin 20 negative (0%). Next-generation sequencing performed on a subset demonstrated recurrent AKT1 E17K mutations in 8 cases (100%) and TP53 alterations in 7 cases (88%). Of 12 cases with clinical follow-up (median: 17 mo), 4 developed cervical lymph node metastases, all of which had colloid or signet ring components. Overall, overlapping histologic and immunohistochemical features coupled with recurrent AKT1 E17K mutations across patterns suggests that mucin-producing salivary adenocarcinomas represent a histologically diverse single entity that is closely related to tumors described as salivary intraductal papillary mucinous neoplasm. We propose a unified mucinous adenocarcinoma category subdivided into papillary, colloid, signet ring, and mixed subtypes to facilitate better recognition and classification of these tumors.

Epithelial-Myoepithelial Carcinoma of the Breast with Rhabdoid Features

Epithelial-myoepithelial carcinoma of the breast is a rare biphasic tumor composed of intermixed malignant epithelial and myoepithelial components. Myoepithelial cells are known to adopt varied morphologies, including spindle, chondroid, clear cell, and rhabdoid morphologies, and can represent a diagnostic challenge when isolated on biopsy. Rhabdomyosarcoma, phyllodes tumor, metaplastic carcinoma, and myoepithelial carcinoma are primary breast tumors that all have been shown to exhibit rhabdoid features, whether representing true differentiation or morphological mimic. We here report an epithelial-myoepithelial carcinoma of the breast with rhabdoid features in a 76-year-old woman. The rhabdoid-appearing myoepithelial cells are negative for myogenin, consistent with a rhabdoid-like morphology rather than a true rhabdoid differentiation, comparably to previously described myoepithelial carcinoma with rhabdoid features. To our knowledge, this is the first reported case of epithelial-myoepithelial carcinoma of the breast with rhabdoid features and thus adds another entity to the differential diagnosis of breast lesions with rhabdoid features.

Adenomyoepithelial tumors of the breast: molecular underpinnings of a rare entity

Adenomyoepitheliomas (AMEs) of the breast are uncommon and span the morphologic spectrum of benign, atypical, in situ, and invasive forms. In exceptionally rare cases, these tumors metastasize to regional lymph nodes or distant sites. In the era of genomic characterization, data is limited regarding AMEs. The aim of this study was to provide insight into the molecular underpinnings of a spectrum of AMEs. Seven cases of AMEs of the breast (benign-1, atypical-2, in situ-1, invasive-3) were identified in our files. The seven samples were interrogated using the Oncomine Comprehensive Assay v3 (ThermoFisher). Two atypical AMEs and the malignant in situ AME harbored the same gain-of-function PIK3CA mutation. The malignant in situ AME also showed EGFR amplification, not described previously. Both a benign AME and a malignant invasive AME shared the same gain-of-function AKT1 variant. The benign AME also showed a GNAS mutation. Moreover, the same gain-of-function HRAS mutation was present in an atypical AME and a malignant invasive AME. We also identified co-occurring HRAS and PIK3CA mutations in an ER-positive atypical AME, which has not been previously described. No fusion drivers were detected. We describe the molecular characteristics of the spectrum of AME tumors of the breast, which harbor alterations in the PI3K/AKT pathway. Our findings are clinically relevant with respect to the current options of targeted therapy in the rare instances where malignant AME tumors of the breast progress.

Juvenile papillomatosis of the breast (Swiss cheese disease) has frequent associations with PIK3CA and/or AKT1 mutations

Juvenile papillomatosis (JP), the so-called Swiss cheese disease, is a rare benign breast disease of young adults. An association (up to 28%) with breast cancer within the family of affected patients has been reported. A multinodular cystic breast mass lesion and calcifications characterizes JP in imaging studies. The histological picture is diverse and comprises multiple intraductal papillomas, usual ductal hyperplasia, ductectasias, perifocal sclerosing adenosis, and calcification. Patients with complete excision of JP lesions have an excellent follow-up; breast cancer develops only on a very low subset of patients. Molecular background of JP has not been investigated until now. In this study, we addressed mutational analysis of JP cases and correlated these results with follow-up and family history in context with a comprehensive review of the JP literature. We identified 13 cases fulfilling the criteria of JP. All patients were women with a median age of 38 years (26-50 years). Follow-up information was available for 11 of 13 patients. Sufficient paraffin-embedded tissue and good DNA quality for next-generation sequencing (NGS) was available for 10 patients. Paraffin blocks were microdissected in the area of intraductal proliferative disease; the tissue cores underwent NGS analysis using the Oncomine Comprehensive Panel. In 5 of 10 patients, we found PIK3CA mutations; in 2 of 10 patients, we found AKT1 mutations in known hot spot regions. Further mutations in MET, FGFR3, PTEN, ATM, NF1, and GNAS genes were detected in individual patients. Some of these mutations were present at high allele frequencies suggesting germ line mutations. Two of 3 patients with positive family history had PIK3CA mutation; one patient with positive family history had an AKT1 mutation. One patient who subsequently developed invasive ductal carcinoma in the contralateral breast possibly had a germ line ATM mutation. Our results confirm hot spot mutations in PIK3CA and AKT1 genes in JP associated with positive family history for breast cancer, although these mutations are not specific for JP. The genetic link between JP, positive family history, and subsequent risk of breast cancer needs to be analyzed in further studies.

Primary Cutaneous Adenomyoepithelioma Ex Spiradenoma With Malignant Histologic Features, Epithelial-Myoepithelial Carcinoma Type: A First Case Report With Molecular Studies

Adenomyoepithelioma is an extremely rare primary cutaneous neoplasm. Although there is ample evidence on the existence of malignant adenomyoepithelioma in the breast, a malignant counterpart in the skin has not been documented. We report a primary cutaneous adenomyoepithelioma (pcAME) with malignant features arising from a spiradenoma in a 39-year-old female patient. The tumor was solid-cystic in appearance and entirely located in the subcutaneous tissue. Histologically, the tumor displayed foci of adenomatous changes and adenomyoepitheliomatous hyperplasia adjacent to a minute spiradenoma. Gradual increase of architectural complexity, cytologic atypia, mitotic activity, and infiltrative growth were observed in a significant portion of the neoplasm, indicative of transformation to adenomyoepithelioma and subsequently low- to high-grade salivary-type epithelial-myoepithelial carcinoma (EMCA). The intimate dual populations of ductal and myoepithelial cells were highlighted by a panel of immunohistochemical stains in all different components of the tumor. Molecular studies revealed a PIKCA3 mutation, a genetic aberration that has been documented in EMCA, particularly of breast origin. The current case documents for the first time a pcAME with malignant features arising from a spiradenoma and suggests adenomyoepithelioma ex spiradenoma as a possible tumorigenesis pathway of this rare cutaneous tumor.

Malignant transformation in a Breast Adenomyoepithelioma Caused by Amplification of c-MYC: A Common pathway to Cancer in a Rare Entity

Breast adenomyoepitheliomas are composed of a biphasic proliferation of myoepithelial cells around small epithelial-lined spaces. Due to the rarity of adenomyoepitheliomas, the molecular data describing them are limited. Adenomyoepitheliomas are considered to be benign or have low malignant potential, and be prone to local recurrence. Malignant transformation has been associated with homozygous deletion of CDKN2A or somatic mutations in TERT, but remains unexplained in many cases. Here, we describe a case of carcinomatous transformation of both epithelial and myoepithelial cells in an estrogen receptor-negative adenomyoepithelioma caused by amplification of MYC. Break-apart fluorescence in situ hybridization revealed an increase in the MYC gene copy number (3–4 copies/cell in 37%, > 4 copies/cell in 40%). Deregulation of MYC is responsible for uncontrolled proliferation and cellular immortalization in basal-like breast cancers. Our case demonstrates that genomic instability events associated with gene amplification may be involved in the carcinogenesis of malignant adenomyoepitheliomas.