[Right Hemi-Colectomy for a Metastatic Transverse Colon Tumor from Breast Cancer Following Bilateral Breast Cancer Resection - A Case Report].

We herein report the case of a 75-year-old female patient who underwent 4 surgeries for bilateral breast cancer and its recurrence. When she presented at a clinic with an irritable colon, a fist-sized tumor was palpated in the right upper abdomen at her first medical examination. Abdominal CT scan at the clinic revealed a tumor with a maximum diameter of 10 cm on the right side of the transverse colon and multiple swollen mesenteric lymph nodes. Therefore, the patient was referred to our hospital for surgery. Colonoscopy revealed stenosis of the same lesion with an edematous mucosa and sclerosis. Using immunohistochemistry, a biopsy specimen from the lesion tested positive for CK AE1+AE3, and negative for CD20(-)and CD3 (-). As a result, the tumor was diagnosed as a poorly differentiated adenocarcinoma. We performed right hemicolectomy to avoid her intestinal obstruction. Tumor cells were mainly present at the subserosa, according to HEstaining. Using immunostaining, the cells were tested for the following markers: CDX2(-), GCDFP15(weakly positive), CK7(strongly positive), CD20(partially positive), E R(+), PgR(-), and HER2(1+), characterizing the tumor as metastasis of breast cancer. Although gastro-intestinal metastasis from breast cancer is rare, and colon metastasis is even rarer, it might be necessary to rule out the possibility of a metastatic colon tumor from breast cancer when treating patients with a colon tumor who have undergone surgery for breast cancer.