[217] Mammary Adenomyoepitheliomas May Feature Basal/Spindle Cells with an Uncommitted Epithelial Phenotype: Biologic and Diagnostic Implications

BC Ho, IO Ellis. Nottingham City Hospital, Nottingham, United Kingdom; Tan Tock Seng Hospital, Singapore, Singapore

Background: Mammary adenomyoepithelioma (AME) is a rare tumour composed of luminal cells and prominent basally positioned polygonal-to-spindle myoepithelial cells, yet the “myoepithelial” nature of the latter cell population remains debatable given their conflicting expression for myoepithelial markers. We aimed to determine the phenotypic characteristics of AME, with particular emphasis on the nature of the so-called myoepithelial cells.
Design: A total of 19 AMEs in 18 patients diagnosed in consultation from January 2004 to September 2009 were reviewed. Immunohistochemistry for p63 (n=16), smooth muscle actin (SMA) (n=17), smooth muscle myosin (SMM) (n=15), CK5/6 (n=16) and CK14 (n=13) was performed using the biotin avidin method and reactivity for each marker was semi-quantitatively assessed. Positive internal controls were available. Focal positivity referred to <25% tumour cells stained.
Results: All patients, aged 40-82 years, presented with clinically or radiologically detected nodular masses, ranging in size from 4 to 60mm. All AMEs showed compact adenotic growth patterns with frequent (74%) central sclerosis and/or infarction.12 AMEs disclosed a focal spindle cell component merging in areas with the basal polygonal cells. On immunohistochemistry, basal/spindle cells of AMEs were commonly reactive for p63 (75%), SMA (94.1%), SMM (73%), CK5/6 (93.8%) and CK14 (100%), although the proportion of cells stained with each marker was highly variable (<5% to 100%). A significant proportion of AMEs contained basal/spindle cells that were either negative or only focally positive for the markers: p63 (37.5%), SMA (29.4%), SMM (60%), CK5/6 (43.8%) and CK14 (23.1%). Notably, 5 AMEs featured CK5/6 and/or CK14 positive basal/spindle cells which were both SMA and SMM negative; these cells occupied more than 50% of the entire basal/spindle cell population in 4 cases and were also p63 negative in 3 cases. In contrast, luminal cells of AMEs never stained with p63, SMA and SMM, but were frequently, albeit variably, positive for CK5/6 (93.8%) and CK14 (100%).
Conclusions: Mammary AMEs may prominently feature basal/spindle cells with an uncommitted epithelial phenotype characterized by basal keratin expression and absence of a myoid signature, the recognition of which may prevent misinterpretation of AME as malignant, particularly on needle core biopsy. While diagnostically useful, CK5/6 and CK14 are by no means specific surrogates for a myoepithelial phenotype.
Category: Breast

Monday, March 22, 2010 1:00 PM

Poster Session II # 40, Monday Afternoon

 

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