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 (). 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.
Mild hypermetabolic lesion was seen in lower inner quadrant of right breast (arrow) and focal hypermetabolic lymph node was seen in right axillary area (arrow head).
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 contralateral breast and axilla were normal.
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. Sonography guided core needle biopsy of the breast mass revealed invasive adenocarcinoma. 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 99mTc-MIBI showed a lesion with increased uptake in the lower inner portion of the right breast with no lesion uptake in the axilla.
Wide excision of the tumor and sentinel lymph node biopsy was performed ().
1.7 cm sized irregular, whitish-gray, firm mass was identified in lower inner portion of right breast, 3.5 cm apart from nipple.
On histopathological examination, 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 (). The harvested sentinel lymph node did not contain tumor cells.
Cuboidal to columnar tumor cells with eosinophilic cytoplasm and pseudostratification were seen on hematoxylineosin stain (×100).
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 (). These findings are consistent with metastatic adenocarcinoma of the colon or rectum.
Immunohistochemistry showed neoplastic cells were positive for CDX2 immunostaining (A, ×200) and cytokeratin 20 immunostaining (B, ×200).
Currently, she is receiving systemic chemotherapy with irinotecan and 5-fluorouracil.