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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.

Aims: Adenomyoepithelioma (AME) and adenoid cystic carcinoma (ACC) of the breast have been noted to occur simultaneously, raising the possibility that AME may represent a related or precursor lesion to ACC. ACC frequently harbours genetic rearrangement of the MYB gene. We sought to clarify the relationship between AME and ACC by comparing their rates of MYB expression by IHC and MYB rearrangement by FISH., Methods and Results: IHC and FISH for MYB rearrangement were performed on paraffin-embedded sections of 11 breast ACCs, 11 non-breast ACCs and 11 breast-AMEs. Using FISH, five of eight (63%) interpretable breast ACCs demonstrated MYB gene rearrangement. Nine of 11 (81%) breast ACCs demonstrated MYB expression (range = 20-95%). Of the three FISH-negative breast ACCs, two were solid variant and demonstrated strong MYB expression by IHC. Of the 10 interpretable non-breast ACCs, six showed MYB rearrangement, all of which were conventional type. Nine of these 11 (81%) cases showed MYB immunoexpression (range = 10-90%), including three solid-variant cases which were negative by FISH. No MYB rearrangements were detected by FISH in 10 interpretable AMEs. However, three of 11 cases (27%) showed weak to moderate MYB expression by IHC (range = 10-40%)., Conclusions: Our results indicate that AMEs do not harbour MYB gene rearrangement. IHC for MYB may be helpful in diagnosing FISH-negative cases of ACC, particularly the diagnostically more difficult solid variants. However, weak to moderate MYB expression in a subset of AMEs highlights not only a potential diagnostic pitfall, but also shared pathophysiology with ACC worth investigating further at the genomic level., (© 2018 John Wiley & Sons Ltd.)

Objective: The identification of myoepithelial cells (MEC) is a valuable clue in the differential diagnosis of breast lesions. A series of breast lesions with occasional absence of or decrease in the staining for some MEC markers was analyzed for the expression of a novel marker, p40, and results were compared to the p63 staining profile., Methods: Samples (n = 34) from patients with benign sclerosing lesions (n = 11), ductal carcinoma in situ (n = 13) and adenomyoepithelial lesions (n = 10) and associated normal breast tissues (n = 31) were selected to evaluate the differential expression of p40 and p63 using immunohistochemistry. Triple-negative, cytokeratin 5 (CK5)-expressing invasive breast carcinomas (n = 19) were also assessed for p40 expression., Results: Normal structures showed similar diffuse and strong MEC positivity using p40 and p63 in all 31 cases. The two antibodies performed similarly in all 34 breast lesions acknowledged to present altered expression of MEC markers; focal losses of expression occurred in a parallel fashion. CK5-positive carcinomas expressed p40 more frequently than p63 (18/19 vs. 8/19) and the staining was more marked., Conclusions: It seems that both antibodies can be used interchangeably for MEC identification, but show differences in the labeling at least in a subset of tumor cells in triple-negative carcinomas., (© 2015 S. Karger AG, Basel.)

Adenomyoepitheliomas of breast are rare tumors. We report for the first time a case of an adenomyoepithelioma of the breast with associated lobular neoplasia. A 53-year-old woman had an annual screening mammogram, which identified areas of asymmetry in her left breast at 4-5-o'clock position. Resection of the masses revealed a well-circumscribed, gray-white, firm discrete nodule (0.8 × 0.4 × 0.3 cm). The tumor was composed of both adenomyoepithelial cell hyperplasia and focal atypical lobular hyperplasia. The 2 cell populations had some overlapping histologic features. Immunohistochemical analysis demonstrated a biphasic proliferation with approximately equal parts of luminal epithelial cells with clear and rounded appearance and myoepithelial cells. The myoepithelial component of the proliferation expressed myosin, p63, CK5/6, S-100, and dimly expressed E-cadherin. The epithelial component of the proliferation strongly expressed E-cadherin. In the areas of atypical lobular hyperplasia, there was distinct loss E-cadherin expression. Awareness of this association is highly important to provide these patients adequate follow-up and treatment., (Copyright © 2014 Elsevier Inc. All rights reserved.)

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.

A small group of tumors of breast and salivary glands contains squamous/epidermoid elements as a constitutive feature (e.g., squamous carcinoma, syringomatous tumors, and mucoepidermoid carcinoma). Other tumors (e.g., pleomorphic adenoma, adenomyoepithelial tumors, and adenoid cystic carcinoma) may show occasionally squamous differentiation. Furthermore, squamous metaplasia may be observed in non-neoplastic breast and salivary tissues. However, the histogenesis of these squamous differentiations is far from being understood. Based on our earlier in situ triple immunofluorescence and quantitative reverse transcription (RT)-PCR experiments for basal keratins K5/14 and p63 as well as for glandular keratins (K7/K8/18), squamous keratins (K10 and K13), and myoepithelial lineage markers (smooth muscle actin, SMA), we here traced the squamous/epidermoid differentiation lineage of 60 tumors of the breast and/or salivary glands, cultured tumor cells of 2 tumors, and of 7 squamous metaplasias of non-neoplastic breast and salivary tissues. Our results indicate that both the neoplastic lesions as well as the non-neoplastic squamous metaplasia contain p63/K5/14+ cells that differentiate toward K10/13+ squamous cells. Thus, cells with squamous/epidermoid differentiation undergo a transition from its original p63/K5/14+ precursor state to K10/13+ squamous lineage state, which can be pictured by triple-immunofluorescence experiments. Given the immunophenotypic similarity of p63/K5/14+ tumor cells to their physiological p63/K5/14+ counterparts in normal breast and salivary duct epithelium, we suggest that these cells provide an important histogenetic key to understanding the pathogenesis of squamous differentiation both in normal breast/salivary gland tissues and their corresponding tumors.

Background: Breast adenomyoepithelioma is an unusual tumor characterized by a biphasic proliferation of epithelial and myoepithelial cells. Most breast adenomyoepitheliomas are considered to be benign or to have a low-grade malignant potential, characterized by propensity for local recurrence. Malignant changes arising in this lesion are extremely rare and may involve one or both cellular components., Case Report: We discuss a case of a 60 year-old woman who began to experience pain in her right breast in January 2009. Breast ultrasound and mammography were performed showing a rounded, hypoechoic solid lesion with ill-defined margins in the right inner-inferior quadrant, suspicious of malignancy. Quadrantectomy of the inner-inferior quadrant of the right breast with sampling of ipsilateral axillary lymph nodes was performed. The histological analysis confirmed the diagnosis of adenomyoepithelioma with focal malignant change of the epithelial component, associated with high-grade malignant myoepithelial change. The patient was treated with adjuvant radiotherapy and her right breast received a dose of Gy 50 with a boost of Gy 10 to the tumor bed. At present, the patient shows no sign of tumor recurrence., Conclusion: Breast malignant adenomyoepithelioma is a rare tumor which should be considered in the differential diagnosis of other solid breast lesions. Only few cases have been reported in the literature. Diagnosis, optimal therapy and predicting the outcome are problematic issues due to the rarity of this disease which appears to have hematogenous rather than lymphatic spread and usually occurs in primary tumors ≥ 1.6 cm in size.

Adenomyoepithelioma is a rare, microscopically distinctive tumor of the skin. This article explores an example that presented in the inguinal area in a 29-year-old woman, mimicking adenopathy. Histopathologically, the tumor included two different areas: a cystic area consisting of tubules and glands in hyalinized stroma and a solid area showing marked myoepithelial proliferation. The diagnosis of adenomyoepithelioma was confirmed by the presence of a biphasic immunoprofile, with expression of cytokeratins and epithelial membrane antigen in the glandular epithelium and with expression of vimentin and smooth muscle actin in the myoepithelial cells. An interesting novel finding was the expression of claudin-10 by myoepithelial cells, which to date has not been reported in the literature. The absence of metaplastic changes in the tumor stroma is crucial in the differential diagnosis with apocrine mixed tumor. Given that soft tissue adenomyoepithelioma is a benign tumor believed to originate from conventional sweat glands, its classification as a cutaneous myoepithelial neoplasm seems reasonable., (Copyright © 2012 John Wiley & Sons A/S.)

Salivary gland-type neoplasms of the breast are uncommon and comprise numerous entities analogous to that more commonly seen in salivary glands. The clinicopathologic spectrum ranges from benign to malignant but there are important differences as compared with those of their salivary counterpart. In the breast, benign adenomyoepithelioma is recognized in addition to malignant one, whereas in the salivary gland a histologically similar tumor is designated as epithelial-myoepithelial carcinoma without a separate benign subgroup. Mammary adenoid cystic carcinoma is a low-grade neoplasm compared with its salivary equivalent. It is also important to appreciate that in contrast to "triple negative" conventional breast carcinomas with aggressive course, most salivary-type malignant breast neoplasms behave in a low-grade manner. Most of these tumors are capable of differentiating along both epithelial and myoepithelial lines, but the amount of each lineage-component varies from case to case, contributing to diagnostic difficulties. Well established examples of this group include pleomorphic adenoma, adenomyoepithelioma, and adenoid cystic carcinoma. Another family of salivary gland-type mammary epithelial neoplasms is devoid of myoepithelial cells. Key examples include mucoepidermoid carcinoma and acinic cell carcinoma. The number of cases of salivary gland-type mammary neoplasms in the published data is constantly increasing but some of the rarest subtypes like polymorphous low-grade adenocarcinoma and oncocytic carcinoma are "struggling" to become clinically relevant entities in line with those occurring more frequently in salivary glands.

Presented herein is the first case of malignant adenomyoepithelioma (malignant AME) of the breast combined with invasive lobular carcinoma (ILC) in a 53-year-old woman. Histologically, the tumor was composed of nodular proliferation of biphasic epithelial and myoepithelial carcinoma, partially surrounded by ILC. Interestingly, ILC metastasized to the axillary lymph nodes, while biphasic epithelial and myoepithelial carcinoma hematogenously metastasized to the lung and the kidney. On immunohistochemistry the biphasic carcinoma consisted of cytokeratin (CK) 8/18-positive/CK5/6-positive/smooth muscle actin (SMA)-negative inner carcinoma cells and CK8/18-positive/CK5/6-positive/SMA-positive outer carcinoma cells. The monophasic ILC cells had a CK8/18-positive/CK5/6-negative/SMA-negative staining pattern. Although it is unclear whether both ILC and biphasic epithelial and myoepithelial carcinoma originated from AME or whether ILC occurred independently of malignant AME, this is an exceptionally rare case, which might give rise to a special consideration of the histogenesis of breast cancer.

We examined a 77-year-old woman who suffered from a left breast tumor. She had undergone right mastectomy for invasive ductal carcinoma at 68 years of age, and rectal resection for mucinous carcinoma at the age of 74 years. The left breast tumor measured 3.8 x 2.5 x 1.6 cm. Neoplastic cells consisted of atypical epithelial and myoepithelial cells. The former cells were polygonal and large. They were located in the periphery of the tumor, arranged in a ductal pattern, and expressed cytokeratins, S-100 protein, maspin, and MIC2. The latter cells were composed of dark cells which proliferated in a periductal pattern, and stellate cells which were located in the center of the tumor. They invaded the chondromyxoid tissues, and proliferated in a lace-like pattern. Atypical myoepithelial cells expressed vimentin, S-100 protein, maspin, and MIC2. We conclude that malignant adenomyoepithelioma of the breast with matrix production might be compatible with a variant form of matrix-producing carcinoma.