mucoepidermoid carcinoma ( mec ) is the most common histological type of both major and minor salivary gland neoplasms . approximately half of these tumors occur in the major salivary glands and the other half occur in the minor salivary glands . mec also arises in the pancreas , lacrimal gland , skin adnexa , bile duct , intestinal mucosa , and breast . mec in the breast represents an unusual variant of breast cancer that accounts for about 0.3% of breast carcinomas . predicting prognosis of mec is difficult as it shows a wide range of low to high grade . a previous study in 1996 showed that mec of the salivary glands exhibits t(11;19)(q21;p13 ) translocation . cytological features of mec breast tumors are similar to mec of the salivary glands and include mucus - secreting , epidermoid , and intermediate cells . because of the rarity of the disease , only a limited number of case series have been published , and thus , the clinicopathological features and clinical outcome of mec of the breast have not been fully investigated . here we report a case of mec of the breast diagnosed by pathological assessment of the lesion . a 71-year - old japanese postmenopausal woman was referred to us for evaluation of a tumor in the right breast . she had suffered from malignant lymphoma ( diffuse , medium to large b - cell lymphoma ) treated with chemotherapy consisting of eight cycles of r - chop and radiotherapy ( total 46 gy ) to the head for the previous 3 years . she had undergone hysterectomy for myoma of the uterus at the age of 41 years . physical examination demonstrated an elastic hard lump on palpation located in the lower lateral quadrant of the right breast . all laboratory data were unremarkable , and there was no increase of tumor markers such as cea and ca15 - 3 . mammography of the right breast showed an unclear mass with accumulation of calcification ( fig 1 ) . ultrasonography showed a hyperechoic lesion within a hypoechoic area , with rough surface ( fig 2 ) . enhanced magnetic resonance imaging revealed a mass of high intensity in the right breast ( fig 3 ) . histopathological evaluation of the core needle biopsy material revealed an invasive adenocarcinoma with metaplastic change , but definitive histological diagnosis could not be determined . the frozen section of the sentinel lymph node was found to be free of disease by intraoperative diagnosis . macroscopically , cut sections revealed a white , solid , and well - circumscribed tumor measuring approximately 17  15 mm ( fig 4 ) . histopathologically , the tumor was composed of cancer cells forming papillary or tubular structures with an abundant mucus cytoplasm , which was positive for periodic acid - schiff staining , and accompanied by psammoma bodies ( fig 5 , fig 6 ) . squamoid cancer cells proliferated in sheet - like patterns , but intracellular bridges or keratinization were not seen ( fig 7 ) . intermediate cells were also seen ( fig 8) . in the stroma , many inflammatory cells proliferated around the tumor . immunohistochemical findings showed that the tumor cells were positive for cytokeratin 7 , cytokeratin 5/6 , cytokeratin 14 , epidermal growth factor receptor , p63 , and muc-1 , and negative for gross cystic disease fluid protein-15 , estrogen receptor , progesterone receptor , and human epidermal growth factor receptor-2 . mec was first reported by foote et al .   as a malignant epithelial neoplasm arising in major and minor salivary glands . salivary gland mec is the most frequent type of salivary gland tumors and represents approximately 30% of malignant tumors of salivary glands . it is characterized by a mixture of mucous - secreting , epidermoid , and intermediate cells . foote et al .   proposed two distinct forms of mec , the low - grade form and high - grade form . recently , goode et al .   proposed a grading system in which five histopathologic features are used to define low- , intermediate- , and high - grade tumors . the 5-year survival rates in low- , intermediate- , and high - grade tumors were 97 , 90 , and 54% , respectively . in high - grade tumors , high ki-67 labeling index ( > 10% ) correlated with decreased patient survival , increased recurrence , and metastasis . the fusion transcript fuses the binding of exon 1 of mucoepidermoid carcinoma translocated 1 ( mect1 ) , a novel gene of unknown function , at 19p13 with exons 25 of a novel member of the mastermind - like gene family ( maml2 ) at 11q21 . this fusion transcript may be specific to mec and associated with a distinct mec subset that exhibits favorable clinicopathologic features and an indolent clinical course . preliminary studies of other carcinoma subtypes of the breast and thyroid are negative for this fusion gene . recently , nakano et al .   reported that her2 gene amplification and an increased egfr gene copy number were detected in high - grade mec irrespective of maml2 fusion status . they suggested that her2 or egfr gene abnormality could play an important role in the development of the progression from maml2 fusion - positive low-/intermediate - grade to high - grade in a subset of mec . in our case , maml2 fusion was not detected using reverse transcriptase - polymerase chain reaction . in 1979 , patchefsky et al . mec of the breast is an unusual variant of breast cancer and similar to its salivary counterpart . the histological features include varying proportions of mucus - secreting , epidermoid , and intermediate cells , as recognized by the world health organization . mec of the breast is rare , with an incidence of approximately 0.3% of all breast cancers . because of the rarity of the disease , only a limited number of case series have been published and thus the clinicopathological features and clinical outcome of mec of the breast have not been fully investigated . horie et al .   described the prognosis of 23 breast mec cases in which 4 patients died of breast cancer , 2 died of other causes , 1 patient remained alive with recurrence , and 14 patients remained alive without recurrence . patients with low - grade mec were disease free in the follow - up period , whereas high - grade mecs usually showed aggressive behavior with metastasis to axillary nodes and distant organs . according to the past reports , no case of mec of the breast with psammoma bodies has yet been described until the current study . psammoma bodies are typically seen in papillary adenocarcinoma of thyroid and meningioma . in mec , the presence of psammoma bodies are frequently observed in thyroid mec rather than salivary or pulmonary mec . maruta et al .   reported that psammoma bodies may be an indicator of lymph node metastasis in papillary adenocarcinoma of thyroid . the significance is unclear , but we can not deny the possibility of a role of psammoma bodies in mec . none of the imaging features of breast lymphoma are pathognomonic . because the imaging features showed atypical findings as invasive breast carcinoma in this case , and our case had a medical history of malignant lymphoma , we considered breast lymphoma as the differential diagnosis . however , histopathologically there was no proliferation of atypical lymphocytes , and thus we did not diagnose breast lymphoma . a previous study reported a case of mec of the parotid grand in a child with acute lymphoblastic leukemia ( all ) treated with chemotherapy and irradiation . in children previously treated for all , second cancers of the salivary glands are most often related to previous head and neck irradiation . mec is the most common cancer of the major salivary glands occurring after irradiation . on the other hand , gibod et al . reported that mec occurred in a patient of all in childhood treated without irradiation , only by chemotherapy . in the current case , she was treated with multidrug chemotherapy and irradiation to the head . the relationship between mec of the breast and lymphoma has not been described , but the possibility of a correlation between the two remains . in conclusion , we report herein a case of mec of the breast . because mec of the breast is a rare entity , there is no standard treatment and the prognostic features are not well established .
a 71-year - old woman , previously treated for malignant lymphoma , was admitted to our hospital with a tumor in the right breast . 
 the tumor size was 2.0 cm in diameter , and the borderline was unclear . 
 the core needle biopsy material revealed an invasive adenocarcinoma with metaplastic change . 
 right mastectomy and sentinel lymph node biopsy was performed . 
 histologically , the tumor was composed of mucus - secreting , epidermoid , and intermediate cells . 
 these findings confirmed the diagnosis as mucoepidermoid carcinoma ( mec ) of the breast . 
 mec is more frequently observed in the salivary glands and occurs rarely in the breast , with an incidence of approximately 0.3% of all breast cancers . 
 because of the rarity of the disease , the clinicopathological features and clinical outcome have not been fully investigated . 
 the relationship between mec of the breast and lymphoma are unclear . here 
 we report a rare case of mec of the breast .