Cancerous Peritonitis Discovered by Uterine Cancer Screening 21 Years after Breast Cancer Surgery—A Case Report—

Abstract

We present the case of a 64-year-old woman with cancerous peritonitis discovered by uterine cancer screening. Abnormalities found during the screening led to a diagnosis of endometrioid adenocarcinoma by the obstetrics and gynecology department. She had undergone a mastectomy of the right breast 21 years previously. Computed tomography (CT) showed bilateral ovarian swelling, para-aortic lymph node metastasis, peritoneal dissemination, and multiple osteosclerosis. Blood tests showed elevated CEA, CA19-9, CA125 and CA15-3, and ascites cytology revealed GATA3-positive atypical cells. A discrepancy between the CT result and the pelvic magnetic resonance imaging result led to the consideration of breast cancer recurrence. A trial laparotomy was performed and the right ovary, mesenteric nodule, and appendix were resected. The histopathological results of the resected specimens were ER-negative, PgR-negative, and HER2-positive in all tissues. The recurrence of HER2-positive breast cancer led to the commencement of docetaxel, trastuzumab, and pertuzumab combination therapy following the operation. Even in cases when the primary cancer site cannot be determined, treatment should be actively considered if there is a promising therapeutic effect.