metastases to the breast from extramammary malignancies are rare and account for 0.43% of all breast malignancies . lymphoma , melanoma , sarcoma , lung carcinoma and ovarian tumor are common extramammary primary malignancies that metastasize to the breast [ 1 - 3 ] . cases of metastasis from primary colorectal neoplasm to the breast is extremely rare . in searching medline and embase including non - english literature , and handsearching the references , we describe the features of metastatic breast cancer from adenocarcinoma of the colon in a 63-year - old woman . a 63-year - old woman was referred to a breast surgeon due to a mass with suspicious metastatic axillary lymph node discovered incidentally on positron emission tomography - computed tomography for follow - up study after colon cancer surgery without other metastatic lesion ( fig . four years ago , she underwent a subtotal colectomy for stage t3n1m0 sigmoid colon cancer with colonic obstruction and subsequent chemotherapy with 5-fluorouracil and leucovorine . two years after the operation , a 2.8 cm sized solitary metastatic lung nodule on the right middle lobe was identified on chest computed tomography for follow - up study for which she underwent pulmonary wedge resection , followed by chemotherapy with oxaliplatin and 5-fluorouracil . physical examination revealed a 2 cm sized firm nodule in the lower inner quadrant of the right breast without evidence of axillary or supraclavicular lymphadenopathy . the mass was not identified on mammography , but ultrasonography showed 1.1 cm sized mass in the lower inner quadrant of the right breast without enlarged lymph node in the ipsilateral axilla . serum tumor markers were all in normal ranges ( carcinoembryonic antigen 4.2 ng / ml , carbohydrate antigen 15 - 3 6.2 u / ml ) . subsequent magnetic resonance imaging showed 1.8 cm sized ill - defined irregular shaped enhancing mass in the lower inner quadrant of the right breast and enlarged lymph node at the ipsilateral axilla compatible with a nodule suspicious for metastasis . breast specific gamma imaging using tc - mibi showed a lesion with increased uptake in the lower inner portion of the right breast with no lesion uptake in the axilla . the tumor cells in the breast mass were cuboidal to columnar with eosinophilic cytoplasm and pseudostratification , compatible with the features of adenocarcinoma of colorectal origin ( fig . immunohistochemical study revealed the following results : tumor cells were strongly positive for cdx2 , cytokeratin ( ck)20 and negative for ck7 , thyroid transcription factor-1 , estrogen receptor , progesterone receptor , c - erbb2 ( fig . 4 ) . these findings are consistent with metastatic adenocarcinoma of the colon or rectum . primary breast cancer is one of the most common malignancies and leading cause of death from malignant disease in women . a malignant mass in the breast can easily be misinterpreted as breast cancer and inappropriate surgical intervention could be carried out . although there are few instances of breast metastasis from colorectal malignancy , correct diagnosis is crucial to avoid unnecessary surgical intervention . generally , metastases to the breast from extramammary malignancies are characterized by rapidly growing , mobile masses that are easily palpable but do not cause overlying skin or nipple retraction , or bloody nipple discharge . core biopsy allows histological assessment of the tissue , helping in identifying the origin of the carcinoma . on the histologic finding , the periductal and perilobular location of the tumor with the absence of in situ ductal carcinoma in the surrounding breast specimen favor a metastasis . immunohistochemistry enables a more confident differentiation between a primary breast adenocarcinoma and a colorectal adenocarcinoma metastasis to the breast . for our patient , diagnosis was finally reached after immunohistochemistry finding . the majority of colorectal carcinomas are usually ck7-negative and ck20-positive , while the majority of primary breast carcinomas is ck7-positive and ck20-negative . and the positive immunostaining for cdx2 is a highly sensitive and specific marker of colorectal carcinoma . our case showed these findings as well ; tumor cells were positive for cdx2 , ck20 and negative for ck7 . recently , some authors have suggested that the expression of ck20 can be identified in primary breast cancer in contrast to the conventional immunohistochemistry results . so , clinicians and pathologists should examine multiple immunohistochemistry markers and combine them as an approach for final diagnosis . according to recent reports , the management of metastatic breast mass from colorectal adenocarcinoma should be diagnostic and palliative . advocated that surgical excision should be avoided in the view of short life expectancy and risk of seeding to the skin . suggested that excisional biopsy was usually appropriate and provided adequate local control . if the diagnosis for the breast mass is unclear , unnecessary intervention , for example mastectomy or lymph node dissection of axilla , can be performed . therefore , when breast mass is identified incidentally on radiologic study during follow - up after operation for colorectal carcinoma , clinicians should keep the possibility of breast metastasis from colorectal adenocarcinoma in mind . additionally , periodical examination of the breast after colorectal cancer surgery may be helpful to detect the metastasis early .
a 63-year - old woman was referred to a breast surgeon with a breast mass discovered incidentally during follow - up study after colon cancer surgery . 
 invasive adenocarcinoma was revealed on core needle biopsy . 
 wide excision of the breast including the tumor was performed . on standard histological examination 
 the tumor showed features of moderately differentiated adenocarcinoma . 
 the immunohistochemistry study revealed positive results for cytokeratin ( ck)20 and cdx2 , but negative for ck7 . 
 these are typical characteristics for colon cancer . 
 considering her history of subtotal colectomy for sigmoid colon cancer , it is presumable that the mass in the breast was of colonic origin , and it was an extremely rare case of metastasis to the breast from primary colorectal neoplasm . although the instance is rare , clinicians should keep the possibility of breast metastasis from colorectal cancer in mind for early and correct diagnosis .