in 1983 , rosen   first described syringomatous adenoma of the nipple ( san ) , a benign tumor of the breast that shows locally infiltrative proliferation and is histologically similar to syringomas . we describe a case of san that is the fourth in japan and the first case reported here within the field of dermatology . the patient was a 51-year - old male office worker who visited the dermatology and allergology clinic of our hospital in july 2009 for evaluation of a subcutaneous nodule in the right breast . he had first noticed the lump 5 years earlier and had become concerned as the lump gradually increased in size . the lesion was a relatively well - circumscribed , elastic , hard , 17-mm subcutaneous nodule adjacent to the areola of the right breast . 1 ) . we considered the lesion likely to be a mammary gland tumor , and the patient was referred to the department of breast surgery for further evaluation . mammography showed a well - circumscribed nodule with a smooth margin on the outside of the upper right breast . these results indicated that the lesion was not a malignant tumor ; furthermore , it was determined that the lesion had not derived from the mammary gland . histopathological analysis revealed several relatively well - circumscribed nodular lesions occurring from within the dermis to the subcutaneous tissue . cells within the nodules showed two phases : ( i ) proliferating tumor cells with compressed duct - like structures surrounded by fibrotic stromal cells and ( ii ) other scattered tumor cells filled with abundant mucus and with no apparent duct - like structures . the highly magnified image of the duct - like structures showed proliferation of multilayered epithelial cell nests forming comma - shaped partial ducts . the duct - like structures were composed of an external layer of relatively pale - stained tumor cells and an internal layer of tumor cells with eosinophilic cytoplasm ( fig . the stromal cells tested positive for alcian blue staining and showed deposition of mucus and hyalinization of collagen fibers . images of dyskaryosis or karyokinesis in the tumor cells were unremarkable . in immunohistochemical staining , the cells within the lesions all tested positive for antibodies to ae1/ae3 , ck7 , cam5.2 , p63 , sma and s-100 protein . the myoepithelial cells were positive for anti - p63 antibody , and the epithelial cells were negative ; thus , the epithelial cell nests showed a biphasic staining pattern , confirming their benign nature . based on the morphological features and the findings of the immunohistochemical staining , these tumors were diagnosed as san . there have been english - language reports on 34 cases of san since rosen   initially reported 5 cases in 1983 ( table 1 ) . san is a locally infiltrative tumor that does not cause distant metastasis ; however , recurrence has been reported in cases of incomplete excision [ 2 , 3 , 4 , 5 , 6 , 7 ] . based on histological classification of mammary gland tumors , differential diagnoses include nipple adenomas and low - grade adenosquamous carcinomas . nipple adenomas are papillary or solid adenomas developing within the nipple where proliferation of papillary epithelium is remarkable [ 1 , 2 ] . low - grade adenosquamous carcinomas that derive from the salivary gland duct show an adenoma - like structure . because they frequently develop in the large and small salivary glands , these carcinomas can be differentiated from their sites of origin . based on histological classification of apocrine and eccrine sweat gland tumors , differential diagnoses include malignant mixed tumors and microcystic adnexal carcinomas ( macs ) [ 9 , 10 ] . malignant mixed tumors are composed of both epithelial and stromal components and have a cartilage - like appearance . macs derive from the eccrine sweat ducts and have an upper layer composed of funicular , keratinous cyst - like and syringoma - like structures , and a lower layer composed of duct - like structures and funicular structures . macs differ from san in that they have a high recurrence rate , compared to a low recurrence rate for san even after conservative excision . another difference is that metastasis of macs has been reported , but there have been no reports of san metastasis . san forms comma - shaped cell nests or small glandular cavities with single or multiple layers of small homogeneous epithelial cells in a background of dense stromal cells . it proliferates and can infiltrate tissue from the nipple to as far as the subareolar stroma . some san differentiate to squamous epithelium . based on morphological features the tumors are likely to have originated from the eccrine sweat ducts remaining in the breast . to our knowledge , only 4 cases of san , including our case , have been reported in japan since 1983 . the cases include 3 women and 1 man , ranging in age from 36 to 87 years ( mean age 63 ) . the sites of origin were the nipple in 3 cases and the areola in 1 case . careful excision is necessary for the treatment of san in order to avoid recurrence of the tumor .
syringomatous adenoma of the nipple ( san ) is an extremely rare disease originating in the adnexal gland ; it was first reported by rosen in 1983 [ am j surg pathol 1983;7:739745 ] . since then , 34 cases have been reported worldwide . 
 we present the case of a 51-year - old man with san , in whom local excision of the tumor was performed . 
 histologically , the tumor consisted of tubules , ductules and epithelial cell strands , and most of the proliferating ducts presented with a characteristic teardrop or comma - shaped appearance .