acinic cell carcinoma ( acc ) of the breast with features of acinar - type differentiation was first described by roncaroli et al .   in 1996 as the breast counterpart of identical tumors of the parotid gland . since then , several cases of acinar cell - like breast carcinoma have been reported [ 1 - 5 ] . these reported carcinomas show diffuse infiltrative growth patterns of small glandular structures and are composed of cells with a coarse granular or clear cytoplasm resembling acinar cells of the salivary glands or paneth cells . we report a case of pure acc of the breast with characteristic histopathological findings , immunohistochemical expression , and ultrastructural zymogen granules in a 39-year - old woman . the tumor is cytologically , immunohistochemically and ultrastructurally very similar to cases of acc of the salivary gland . our differential diagnosis with microglandular adenosis ( mga ) , and other carcinomas showing granular cytoplasm is discussed . a 39-year - old woman presented with a 1-year history of a palpable breast mass . a fine - needle aspiration ( fna ) of the mass was performed under the initial clinical diagnosis of benign fibroadenoma . the fna result was atypical cytology , and showed scattered or rarely clustered , uniformly round cells with small nuclei and a moderate amount of cytoplasm , suggesting a benign or low grade malignant tumor . the tumor was a 5.53.0 cm , ill defined , gray - brown with a rubbery consistency , and a slightly lobulated appearance ( figure 1 ) . microscopically , the tumor showed a diffuse infiltrative growth patterns with small acinar or glandular structures mixed with solid nests ( figure 2 ) . most of the tumor was comprised of monotonous round cells with a finely granular , weakly eosinophilic , or clear vacuolated cytoplasm resembling acinar cells of the salivary glands . morphologically distinct cells showed dark eosinophilic coarse granules resembling paneth cells ( figures 3 , 4 ) . the lumen of the small acinar or glandular structure sometimes contained red colloid - like material and microcalcifications . these large solid tumor cell nests revealed central comedo - like necrosis , reminiscent of ductal carcinoma in situ ( figure 5 ) . however , these cells were also cytologically and immunohistochemically closely similar to typical acinar cells . the mitotic count was high in areas with more solid nests ( up to 5 - 35/high power field ) , but lower in areas with acinar cells ( up to 0 - 3/high power field ) . periodic acid - schiff ( pas ) stain demonstrated strong staining of cytoplasmic granules with diastase resistance . immunohistochemically , both the glandular and solid tumor cell populations were strongly positive for lysozyme ( figure 6a ) , -1-antitrypsin , and epithelial membrane antigen ( ema ) . staining showed complete circumferential intense staining for e cadherin ( figure 6b ) and focal cytoplasmic reactions for the s-100 protein ( figure 6c ) . focal neoplastic cells were weakly positive for cytokeratin ( ck ) 7 ( figure 6d ) , compared to a strongly positive reaction in normal ducts and lobules . the other areas were negative for estrogen receptor , progesterone receptor , gross cystic disease fluid protein of 15 kda ( gcdfp 15 ) , cytokeratin 20 , muc2 , muc5a , muc6 , neuron specific enolase , cd68 , smooth muscle actin , and human epidermal growth factor receptor-2 ( her2/neu ) ( table 1 ) . electron microscopy performed with formalin - fixed tissue demonstrated numerous variable sized electron dense granules in the cytoplasm that were consistent with zymogen granules , and a prominent , rough endoplasmic reticulum ( figure 7 ) . the patient was transferred to an another hospital for a breast conserving operation with a sentinel node biopsy and axillary node dissection . only one non - sentinel node revealed metastatic carcinoma , measuring 0.3 cm at the greatest dimension . similar to the salivary glands , the breast has modified sweat or apocrine glands , and some tumors arising in the breast are subject to development of salivary type tumors , such as pleomorphic adenoma , adenoid cystic carcinoma , adenomyoepithelioma , and acc . emphasized that breast tumors with salivary gland differentiation originate from a malignant transformation of terminal duct - lobular units with metaplastic changes . furthermore , the immunohistochemical profile of the tumor reported herein was identical to that of salivary acc . lysozyme can be detected in mammary epithelium during lactation and lactating lobules share a similar immunophenotype with breast acc . previous reports have shown that the pathogenesis of acc is related to mga or secretory carcinoma ( sc ) . however , these reports noted no relationship between mga or sc and acc based on a lack of etv6 rearrangement in acc . therefore , acc is a distinct entity other than one variant or a related lesion . described the differential points of mga , pointing out that acc of the breast has a microglandular growth pattern , luminal eosinophilic colloid - like secretory materials , and diffuse and intense positive immunoreactivity for the s-100 protein . however , acc shows immunoreactivity for ema , lysozyme , amylase , and -1-antichymotrypsin . while the glands in mga are surrounded by a basal lamina , the neoplastic glands of acc do not possess a basal lamina . microscopically , acc of the breast reveals two morphologically distinct cell populations focally merging into one another . the present tumor showed a diffuse infiltrative growth pattern with small acinar or glandular structures mixed with solid nests ( figure 2 ) . the solid nests , commonly observed in in situ and invasive ductal carcinoma , were focally recognized in the present case . these large solid tumor cell nests showed central comedo - like necrosis , which is reminiscent of ductal carcinoma in situ ( figure 5 ) . however , these cells were also cytologically and immunohistochemically closely similar to typical acinar cells . both glandular and solid tumor cell populations were strongly positive for lysozyme ( figure 6a ) , -1-antitrypsin , and ema . the tumor cells were negative for gcdfp 15 , estrogen receptor , progesterone receptor , and her2/neu . re - evaluation of the present case led to a diagnosis of pure acc , due to the immunohistochemical results . studied acinar cell differentiation in salivary gland tumors and noted the presence of zymogen - type granules . zymogen is only one of the components in acc , as amylase , lysozyme and -1-antichymotrypsin are also constituents of salivary gland acinar cells . they found amylase expression in all breast tumors studied , as well as in all studied cases of acc of the parotid gland . electron microscopy demonstrated numerous variable sized electron dense zymogen granules in the cytoplasm , that were consistent with acinar cell granules . intense immunohistochemical expression of lysozyme and -1-antitrypsin combined with ultrastructural findings of numerous zymogen granules confirmed the diagnosis of acc of the breast . all patients were 35 - 80 years ( mean - age , 56 years ) . axillary dissection was performed in three cases , and lymph node metastases were found in two . of the six patients , one was alive and well after 5 years , three were alive and well after 1 year , one had a recurrence after 4 years , and one was lost to follow - up . these cases demonstrate that primary acc of the breast can be associated with a poor prognosis , particularly when the tumor is high grade with additional adverse prognostic features . the present case was a high grade invasive solid tumor with a high mitotic count for small limited foci . peintinger et al .   suggested that acc of the breast belongs to a group of clinically low - grade malignant tumors , even with some unfavorable prognostic parameters such as high mitotic activity and steroid hormone receptor negativity . in summary , this case was histologically , immunohistochemically , and ultrastructurally typical of pure acc of the breast .
acinic cell carcinoma ( acc ) of the breast is extremely rare and is characterized by widespread acinar cell - like differentiation . 
 we report of a 39-year - old woman presented with a palpable breast mass with significant morphological , immunohistochemical and ultrastructural findings . 
 histologically , acc showed a diffuse glandular infiltrative pattern , with small acinar or glandular structures mixed with solid nests . 
 neoplastic cells were monotonous proliferation of cells with a granular or clear cytoplasm , resembling acinar cells of the salivary glands or paneth cells . 
 both glandular and solid tumor cell populations were strongly positive for lysozyme and -1-antitrypsin .