A rare case of primary rectal adenocarcinoma metastatic to the breast.

Primary rectal adenocarcinoma metastatic to the breast is an exceedingly rare event. Its management differs from that of primary breast cancer, as illustrated by this case. A 63-year-old woman presented with a breast lump 30 months after abdominoperineal resection for rectal adenocarcinoma, stage T₃N₁M₀ (stage III), followed by standard postoperative radiochemotherapy. The patient underwent a mammography and ultrasonography. A CT scan of the abdomen showed metastatic disease. An excisional biopsy of the breast lump was performed; morphological features were identical to the original rectal cancer. Immunohistochemical results were negative for estrogen and progesterone receptors and gross cystic disease fluid protein-15, and intensity positive for cytokeratin 20 and carcinoembryonic antigen. The patient died after treatment with palliative chemotherapy. Metastatic disease from rectal carcinoma to the breast is a marker for disseminated metastatic spread with poor prognosis.