mucinous cystadenocarcinoma ( mca ) is a very rare breast tumor . to our knowledge , only 18 cases of mca have been published in the english literature , mostly focusing on the pathologic findings . mca is a pathologically distinct disease entity ; however , radiologic findings have not yet been described in precise detail . here , we report mammographic , ultrasound ( us ) , and magnetic resonance imaging ( mri ) findings of primary breast mca in two patients , and review the literature focusing on imaging findings . a 59-year - old woman presented with a mass in her left breast detected on screening mammography . she was postmenopausal and did not have a family history of breast cancer or other malignancy according to her medical records . physical examination revealed a 1.5 cm mass in the upper outer quadrant of the left breast , 5 cm from the nipple . mammography showed a lobular - shaped circumscribed hyperdense mass , containing round or punctate microcalcifications ( figure 1a ) . on us , the mass was located at the far periphery of the left upper outer breast and appeared as a circumscribed complex cystic and solid mass . the solid portion of the mass showed an irregular shape and isoechogenicity , with multiple echogenic dots corresponding to the microcalcifications seen on mammography ( figure 1b ) . the solid portion showed low signal intensity ( si ) on t1 weighted imaging ( wi ) ( figure 1c ) and intermediate si on t2 wi ( figure 1d ) . on dynamic contrast - enhanced images , the mass showed rim enhancement and nodular enhancement of the solid portion with persistent enhancement kinetics ( figure 1e ) . the result of percutaneous core needle biopsy using a 14-gauge gun was intraductal carcinoma with mucin spillage . the differential diagnosis based on the percutaneous biopsy result was mucocele - like lesions with ductal carcinoma in situ or mucinous carcinoma with ductal carcinoma in situ . after partial mastectomy , a 2.0 cm mca with bloom - richardson grade i was diagnosed . most nuclei were basally located and somewhat bland ; however , some nuclei showed more atypia ( figure 1f ) . the tumor cells were negative for estrogen and progesterone receptors but were positive for human epidermal growth factor receptor 2 ( her2 ; 3 + ) . she was premenopausal and had no family history of breast cancer or other malignancy according to her medical records . the mass showed obscured margins and had a few faint microcalcifications ( figure 2a ) . the solid portion of the mass showed hypoechogenicity and had a partially indistinct margin ( figure 2b ) . on doppler us , no increased vascularity or vascular stalk was noted ( figure 2c ) . on mri , the mass in the left mid outer breast was shown to be cystic and solid . the solid portion showed an irregular shape and margin , had hypointensity on t1 wi ( figure 2d ) , intermediate si on t2 wi ( figure 2e ) , and heterogeneous enhancement with persistent enhancement kinetics ( figure 2f ) . percutaneous core needle biopsy using a 14-gauge gun found cystically dilated atypical mucinous glands , and mca was suspected . after a left partial mastectomy , a 2.2 cm mca with bloom - richardson grade iii was diagnosed ( figure 2 g , h ) . multiple variable sized cysts were filled with mucin . in this case , the mucinous epithelium showed marked atypia and pleomorphism . the tumor cells were negative for estrogen and progesterone receptors and were also negative for her2 . a 59-year - old woman presented with a mass in her left breast detected on screening mammography . she was postmenopausal and did not have a family history of breast cancer or other malignancy according to her medical records . physical examination revealed a 1.5 cm mass in the upper outer quadrant of the left breast , 5 cm from the nipple . mammography showed a lobular - shaped circumscribed hyperdense mass , containing round or punctate microcalcifications ( figure 1a ) . on us , the mass was located at the far periphery of the left upper outer breast and appeared as a circumscribed complex cystic and solid mass . the solid portion of the mass showed an irregular shape and isoechogenicity , with multiple echogenic dots corresponding to the microcalcifications seen on mammography ( figure 1b ) . the solid portion showed low signal intensity ( si ) on t1 weighted imaging ( wi ) ( figure 1c ) and intermediate si on t2 wi ( figure 1d ) . on dynamic contrast - enhanced images , the mass showed rim enhancement and nodular enhancement of the solid portion with persistent enhancement kinetics ( figure 1e ) . the result of percutaneous core needle biopsy using a 14-gauge gun was intraductal carcinoma with mucin spillage . the differential diagnosis based on the percutaneous biopsy result was mucocele - like lesions with ductal carcinoma in situ or mucinous carcinoma with ductal carcinoma in situ . after partial mastectomy , a 2.0 cm mca with bloom - richardson grade i was diagnosed . most nuclei were basally located and somewhat bland ; however , some nuclei showed more atypia ( figure 1f ) . the tumor cells were negative for estrogen and progesterone receptors but were positive for human epidermal growth factor receptor 2 ( her2 ; 3 + ) . she was premenopausal and had no family history of breast cancer or other malignancy according to her medical records . the mass showed obscured margins and had a few faint microcalcifications ( figure 2a ) . the solid portion of the mass showed hypoechogenicity and had a partially indistinct margin ( figure 2b ) . on doppler us , no increased vascularity or vascular stalk was noted ( figure 2c ) . on mri , the mass in the left mid outer breast was shown to be cystic and solid . the solid portion showed an irregular shape and margin , had hypointensity on t1 wi ( figure 2d ) , intermediate si on t2 wi ( figure 2e ) , and heterogeneous enhancement with persistent enhancement kinetics ( figure 2f ) . percutaneous core needle biopsy using a 14-gauge gun found cystically dilated atypical mucinous glands , and mca was suspected . after a left partial mastectomy , a 2.2 cm mca with bloom - richardson grade iii was diagnosed ( figure 2 g , h ) . multiple variable sized cysts were filled with mucin . in this case , the mucinous epithelium showed marked atypia and pleomorphism . the tumor cells were negative for estrogen and progesterone receptors and were also negative for her2 . mca is characterized by cystic lesion containing mucin lined by columnar cells with abundant intracytoplasmic mucin or mucin - depleted columnar cells , while mucinous carcinoma is characterized by clusters of generally small and uniform cells floating in large amount of extracellular mucin . previous reports have mostly focused on pathologic findings , with only a few reports briefly describing radiologic findings , providing few details . mammographic findings of mca have been described in several case reports , and the most common finding was a well - defined multilobular mass with medium to high density . our cases showed lobular shaped masses with relatively circumscribed margins and round to punctate internal microcalcifications . reported us findings of primary breast mca are mostly circumscribed isoechoic to hypoechoic masses ; occasionally , irregular masses or cystic and solid masses have also been reported . one case showed a circumscribed complex cystic mass with a small solid portion , whereas the other showed a more solid portion with an irregular shape and indistinct margins . mri findings have not been described previously . in our cases , both tumors showed cystic and solid masses and the cystic portion of the masses showed a circumscribed margin and thin rim enhancement . the intracystic solid portion of the tumor showed nodular enhancement and a large irregular solid mass with heterogeneous enhancement . both showed persistent enhancement kinetics on dynamic enhancement images and intermediate si on t2 wi . in our cases , from the us findings of a complex cystic and solid mass , we considered the possibility of papillary neoplasm first . however , a vascular stalk or increased vascularity , which is a characteristic finding of papillary neoplasm , was not detected . on mri , our cases also showed a cystic portion with rim enhancement and an intracystic solid portion , which may suggest a papillary tumor . however , the enhancement kinetics of our cases was persistent , while papillary neoplasms commonly show washout enhancement kinetics . in the first case , the percutaneous biopsy result was intraductal carcinoma with mucin spillage , suggesting the possibility of mucinous carcinoma . however , us showed a cystic mass with a small intracystic nodule with microcalcifications , which is not the typical finding for mucinous carcinoma , namely , an isoechoic solid mass with heterogeneous echotexture and a circumscribed or microlobulated margin . mucinous carcinoma can also show cystic changes within the solid tumor because of the mucin pool , but our case showed a large cyst with a small nodule similar to intracystic papilloma rather than cystic changes within the solid tumor . moreover , the microcalcifications on mammography were small and round rather than the coarse and heterogeneous microcalcifications commonly detected in mucinous carcinoma . on mri , the solid portion of the tumor showed an intermediate signal on t2 wi that was not as bright as that usually seen in the typical mucinous carcinoma . mucocele - like lesions also show mucinous material in percutaneous biopsy samples , and they can have various shapes of calcifications on mammography . however , they are usually benign cystic masses , including simple cysts , complicated cysts , and clustered microcysts , rather than complex cystic and solid masses , unless they are associated with atypical ductal hyperplasia or malignancy . in conclusion , mca shows a circumscribed mass with some lower suspicion microcalcifications on mammography , and shows an intracystic solid mass without increased vascularity or a vascular stalk on us . on mri , the solid portion shows intermediate si on t2 wi and heterogeneous enhancement , and the cystic portion shows rim enhancement . when the above - described findings are detected during radiologic exams , and mucinous material is present in the biopsy specimen , mca can be considered as a differential diagnosis .
primary mucinous cystadenocarcinoma ( mca ) of the breast is a rare but pathologically distinct breast tumor . 
 there have been some case reports on primary mca of the breast ; however , they have all focused on pathologic findings . here , we report the radiologic findings of two cases of mca along with a review of the literature . 
 breast mca shows a circumscribed mass with some calcifications on mammography , an intracystic solid mass without increased vascularity or a vascular stalk on ultrasound , and a heterogeneously enhancing mass within a rim - enhancing cyst with intermediate signal intensity on t2-weighted magnetic resonance imaging . 
 these radiologic findings and the presence of mucin in the percutaneous biopsy specimen should suggest the possibility of mca in the differential diagnosis of a breast tumor .