contralateral axillary lymph node metastases ( cams ) are an uncommon finding in breast cancer . the reported incidence of cam varies between 3.5 and 6% for all breast cancers [ 1 , 2 , 3 ] . axillary lymph node metastasis from an occult breast cancer is also an uncommon presentation , accounting for 0.31% of all breast cancers . moreover , clinicians may face management dilemmas in cases of cam because they must consider the possibility of occult primaries in the contralateral breast or tumors outside the breast . in most cases , cams and contrary to these expectations , we encountered a case in which synchronous contralateral metastatic lymphadenopathy and the primary breast cancer differed in terms of both hormonal receptor statuses and human epidermal growth factor receptor 2 ( her2 ) expression . a 43-year - old premenopausal woman presented with three non - palpable breast tumors on screening with breast ultrasonography . the breast tumor sizes were as follows : 6 mm [ breast imaging - reporting and data system ( bi - rads ) category 3 ] in the right breast , 6 mm ( bi - rads category 5 ) in the left breast , and 5 mm ( bi - rads category 3 ) in the left breast . multiple pathological lymph nodes were discovered in the right axilla , but no pathological entities were found in the left axilla after ultrasonography . ultrasound - guided core needle biopsy was performed for the bi - rads category 5 lesion in the left breast . lesions of 8 mm ( bi - rads category 3 ) in the right breast , 4 mm ( bi - rads category 6 ) in the left breast , and 5 mm ( bi - rads category 3 ) in the left breast were found by magnetic resonance imaging . 18-fluorodeoxyglucose positron emission tomography showed a positive uptake in the right axilla without abnormal hypermetabolic lesions in the breasts , and no definitive evidence of distant metastasis ( fig . 1 ) . left breast - conserving surgery , left sentinel lymph node biopsy , right breast mass excision , and right axillary lymph node dissection were performed . histopathological examination of the left breast mass revealed a 0.7-cm grade ii idc and no lymphovascular invasion . although no metastasis was found in three left sentinel lymph nodes , three metastases were found in 25 right axillary lymph nodes ( fig . the left breast tumor specimen was revealed to be positive for estrogen receptor ( er ) ( fig . immunohistochemical analysis revealed positive cytokeratin 7 ( ck7 ) , negative ck20 , positive ck19 ( fig . 2h ) , and negative thyroid transcription factor-1 ( ttf-1 ) staining in the right axillary lymphadenopathy . to exclude the possibility that the patient had other primary tumors , computed tomography of the neck , chest , and abdomen as well as gastrofiberscopy and colonofiberscopy were performed . postoperatively , the patient was treated with four cycles of adjuvant chemotherapy consisting of doxorubicin and cyclophosphamide as well as four cycles of docetaxel . after adjuvant chemotherapy , radiation therapy was administered to both breasts and right supraclavicular lymph nodes . two years after diagnosis , she is free of disease and presently being treated with tamoxifen . lymph node metastasis of breast cancer mostly occurs in the ipsilateral axilla . in most studies of cam , further , in a case series by huston et al . , only 1 of 7 patients had synchronous cam . reported aggressive histopathological features in patients who have breast cancer with cam , such as higher tumor grade , lymphovascular invasion , larger primary tumors , er - negativity , and her2 overexpression . however , in our report , the primary breast tumor was a grade ii idc , with er - positivity , no lymphovascular invasion , and no her2 overexpression . as noted previously , the histopathological and immunohistochemical features of cam are generally similar to those of the primary breast cancer . for example , huston et al .   observed the same histological and immunohistochemical features in cams and their primary tumors in the contralateral breasts . however , in our case , immunohistochemical analysis of the primary breast lesion revealed er+ , pr+ , and her2 tissue , even though the contralateral axillary lymphadenopathy was er , pr , and her2 + . these findings can make it difficult for clinicians to predict disease prognosis and establish a therapeutic strategy . if an occult breast cancer is a source of the metastatic lymphadenopathy in the contralateral axilla , the present case might be classified as bilateral breast cancer . breast magnetic resonance imaging has been helpful to detect occult primary lesions in the breast [ 6 , 7 ] . in our case , breast magnetic resonance imaging to detect the presence of an occult primary tumor found a benign mass ( bi - rads category 3 ) in the right breast . although we undertook imaging studies and other investigations to identify extra - mammary tumors , no abnormal findings were uncovered . ck7-positive , ck20-negative , ck19-positive , and ttf-1-negative stainings were found in the immunohistochemical studies of cam . the combination of these findings suggests that the breast is the primary site of the axillary lymph node metastasis . contralateral lymphadenopathy with primary breast cancer may occur because of cam , an occult primary tumor in the contralateral breast , or an extra - mammary tumor . to confirm the diagnosis of synchronous cam , it is essential to exclude the presence of occult primary cancers and extra - mammary tumors . this case suggests that specific tests and thorough investigations should be performed by clinicians who may face cases of dissimilar cam and primary breast cancer . we have reported this case because it presents initial evidence regarding the very rare occurrence of synchronous cam and primary breast cancer with different histopathological features .
we report the case of a 43-year - old woman with primary left breast cancer presenting metastatic lymphadenopathy in the contralateral axilla . 
 this patient represents a diagnostic and therapeutic challenge because primary breast cancer , occult contralateral breast cancer , and extra - mammary primary lesion can all be the source of the contralateral axillary metastasis . 
 left breast - conserving surgery , left sentinel lymph node biopsy , right breast mass excision , and right axillary lymph node dissection were performed . 
 immunohistochemical analysis revealed that the left breast cancer specimen was positive for estrogen receptor ( er ) and progesterone receptor ( pr ) , but negative for human epidermal growth factor receptor 2 ( her2 ) . 
 in contrast , the right axillary lymphadenopathy specimen was negative for er and pr , but positive for her2 . 
 further investigation revealed no evidence of occult primary cancers or extra - mammary tumors . 
 after surgical intervention , the patient was treated with adjuvant chemotherapy , adjuvant radiation therapy , and targeted therapy with trastuzumab . 
 two years after diagnosis , she is free of disease and presently being treated with tamoxifen .