Poorly differentiated mesenteric carcinoma of unknown primary site detected by abscess formation: case report

BACKGROUND Carcinoma of unknown primary site (CUP) is said to account for approximately 3 to 5% of all carcinomas. However, an isolated lesion in the abdominal cavity is rare, and there are no reports describing associated abscess formation. CASE PRESENTATION A 76-year-old woman had consulted a previous physician complaining of fever and right lower quadrant abdominal pain. Enhanced computed tomography (CT) showed an abscess formation around the cecum. She was treated conservatively with antibiotics, but the symptoms relapsed and she consulted our hospital. Enhanced CT showed a persistent abscess, a tumorous lesion in the mesentery and right hydronephrosis. Because malignancy could not be ruled out, surgical treatment was selected. At laparotomy, encapsulated abscesses were found on the mesenteric side and outside of the ileocecal region. When we raised the ileocecal region, a tumor was found to be fixed to the right ureter, and there was leakage of white, solid tumor content. This tumor content was submitted to intraoperative frozen section diagnosis which revealed a carcinoma. Ileocecal resection with D3 lymph node dissection and retroperitoneal tumor resection was thus performed. There were no abnormal findings in the uterus and adnexa, nor any evidence of peritoneal dissemination. We regarded this case as an incomplete resection and chemotherapy with paclitaxel and carboplatin was administered. The patient has remained alive and disease-free for almost one year since the primary operation. CONCLUSION We described a case with mesenteric CUP discovered during surgery for an intra-abdominal abscess. It is necessary to pay attention to treatment-resistant intraperitoneal abscesses as they may accompany a tumor.