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Introduction: Many patients who undergo coronary artery bypass surgery have a prior history of cancer and potentially chest radiation which is a known risk factor for coronary atherosclerosis. Prior radiation increases fibrosis and can make the dissection of the left internal mammary artery (LIMA) more challenging.Case Report: A 72-year-old woman with a history of stage IIA pT2N0M0 left breast intraductal carcinoma treated with lumpectomy, adjuvant chemotherapy and radiation therapy 11 years prior presented to the emergency room with a non-ST elevation myocardial infarction and was taken for cardiac catheterization followed by three-vessel coronary artery bypass grafting. The LIMA was found to be encased in scar tissue and was deemed unsuitable as a conduit, and a saphenous vein graft was bypassed to the left anterior descending artery in its place. Pathologic review of the LIMA showed nests of tumor cells infiltrating within dense fibrous tissue with areas of necrosis and calcifications consistent with recurrent breast cancer. Interestingly the patients original breast cancer was positive for estrogen receptors (ER) and progesterone receptors (PR) ER and PR and negative for HER2 and she had therefore been treated with 5 years of hormonal therapy. The recurrent cancer found in the LIMA dissection bed at the time of bypass surgery was ER, PR, and HER2 negative, suggesting hormonal therapy driven clonal selection of these metastatic tumor cells.Discussion and Conclusions: Scarring in the LIMA dissection bed in patients with a history of cancer and prior chest radiation should be carefully evaluated for the possibility of recurrent cancer. The gross appearance of tissue can be misleading and sending a biopsy for a formal frozen section histologic evaluation should be considered if there is any question of recurrent malignancy. [ABSTRACT FROM AUTHOR]