adenomyoepithelioma has been described as a rare benign neoplasm that occurs almost exclusively in the breast . in the breast
it is defined as a neoplasm composed of two structures , namely , tubules limited by an inner epithelial layer of duct - like cells and an outer layer with mostly clear myoepithelial cells .
apart from the breast , adenomyoepitheliomas have been described in the salivary glands and in the lung . in the skin ,
these neoplasms seem to be exceedingly rare , with only few reports of adenomyoepitheliomas published to date [ 47 ] .
we present the case of a 53-year - old woman with a clinically benign nodular cutaneous lesion that revealed histopathologic and immunohistochemical features of adenomyoepithelioma .
a 53-year - old woman presented to her dermatologist with a 3 cm asymptomatic nodule on the left forearm .
the biopsy specimen consisted of a 2.5  1.9  1.5 cm tan ellipse of skin and contained a hard yellow nodule measuring 1.5 cm in greatest dimension .
examination of the sections at scanning magnification revealed beneath an intact epidermis a zone of fibrosis within the upper part of the dermis ( figure 1 a , b ) . beneath the scar
, there was a large , lobulated neoplasm , which for the most part was surrounded by a compressed fibrous pseudocapsule .
each of the aggregates of neoplastic cells varied in sizes and shapes and some were large and nodular ( figure 1a  c ) . at higher magnification , most of the cells that constituted the lesion displayed myoepithelial differentiation with polygonal and  plasmacytoid  features ( figure 2 ) .
the cells presented sometimes as solid sheets , but also as cords and solitary units . in places glandular and ductal structures were evident ; in some areas apocrine - type secretion within glandular structures was found ( figure 2 a  c ) .
f ) . in some areas cells were present within a myxoid stroma ( figure 2 g 
foci of cells with pleomorphic nuclei and mitotic figures were identified ( figure 2 k 
the myoepithelial cellular component of the neoplasm stained for s100 protein and was negative for cytokeratin and carcinoembryonic antigen ( cea ) expression .
we describe a cutaneous neoplasm composed of myoepithelial cells and a focal epithelial and glandular component .
the s100 positivity indicates myoepithelial cells , while epithelial - glandular cells are negative for s100 protein expression .
based on findings by conventional microscopy and immunohistochemistry , this neoplasm shows myoepithelial differentiation and focal epithelial lined tubules with features of apocrine secretion , findings that are consistent with the diagnosis of primary adenomyoepithelioma of the skin .
while various adnexal neoplasms with a myoepithelial cellular component have been described in the skin , adenomyoepithelioma of the skin seems to be extremely rare .
what are the criteria that distinguish adenomyoepithelioma from other benign cutaneous neoplasms with myoepithelial differentiation ? while myoepithelioma is defined as a benign neoplasm consisting exclusively of myoepithelial cells embedded in a myxoid stroma , adenomyoepithelioma shows in addition to myoepithelial cells a second component displaying various degrees of epithelial - ductal differentiation .
chondroid syringoma ,  at the other end of the spectrum is a benign adnexal neoplasm that , in addition to apocrine epithelium , manifests various degrees of follicular and/or sebaceous differentiation .
clinically , myoepitheliomas occur usually in children and young adults and are located on the extremities , while mixed apocrine tumors affect older individuals and are usually found on the face .
the few cases of cutaneous adenomyoepitheliomas that have been described to date , including the present case , were described in older patients and were located on the extremities and on the trunk .
pleomorphic adenoma in the breast is regarded as the analogue to mixed apocrine tumor in the skin , while adenomyoepithelioma of the breast is defined as a neoplasm with nodular aggregations of clear myoepithelial cells that surround epithelial lined tubules .
occasionally , the myoepithelial component predominates and loses the close association with epithelial structures . in the skin
, the predominance of myoepithelial cells in relation to ductal epithelial structures lacking features of follicular and/or sebaceous differentiation separates this neoplasm from mixed apocrine tumor .
therefore , myoepithelioma , adenomyoepithelioma and mixed apocrine tumor lie in the spectrum of neoplasms with pure myoepithelial differentiation at one end and apocrine - sebaceous - follicular differentiation at the other .
the most important question for the patient is the biologic potential of such a lesion . while the chronic course in our patient and the majority of the histopathologic features suggest a benign neoplasm , foci of cells having pleomorphic nuclei and mitotic figures were present .
both findings could indicate the potential for locally aggressive behavior and/or metastasis , as has been rarely described in adenomyoepitheliomas of the breast .
therefore , adenomyoepitheliomas of the skin should be completely excised , as has been recommended in the reported case .
 analogous to adenomyoepitheliomas of the breast , cutaneous adenomyoepithelioma is composed of two components , one being myoepithelial , the other ductal epithelial , and it lies in the spectrum of neoplasms having a  pure  myoepithelioma at one end and a mixed apocrine tumor at the other . 
 we present the case of a 53-year - old woman with a 3 cm nodular lesion on her left forearm that had been present for many years . 
 histopathologic examination revealed a large lobulated neoplasm surrounded by a compressed fibrous pseudocapsule . 
 most of the cells that constituted the lesion displayed myoepithelial differentiation arranged in solid sheets , cords , and solitary units . 
 glandular and ductal structures with features of apocrine differentiation composed the second part of the neoplasm . the myoepithelial cellular component of the neoplasm stained for s100 protein and was negative for cytokeratin and carcinoembryonic antigen ( cea ) . based on findings by conventional microscopy and immunohistochemistry , 
 the neoplasm was classified as primary adenomyoepithelioma of the skin . 
Introduction
Case report
Conclusions