[A Rare Case of Retroperitoneal Metastasis from Ascending Colon Cancer That Required Multimodal Treatment].

A patient in his 70's underwent a right hemi-colectomy due to an ascending colon cancer in a previous hospital. The tumor had widely infiltrated the retroperitoneal space(pT3, pN0[0/12], pPM0, pDM0, pRM1, Stage II ). He was referred to our institute 1 month after primary surgery to receive chemotherapy for his residual tumor. Abdominal computed tomography (CT)showed a 24mm tumor in his retroperitoneal space before chemotherapy. After 4 cycles of mFOLFOX6 and panitumumab, the tumor partially responded, and after 7 cycles, he achieved a complete response(CR). After an additional 10 cycles, he had maintained the CR, and chemotherapy was discontinued. Two years and 11 months after discontinuation of chemotherapy, an abdominal CT revealed a tumor that gradually grew behind the right kidney. The tumor was resected, and pathological findings showed it was recurrence of the past colon cancer. Seven months after resection of recurrent tumor, CT revealed 2 newly recurrent tumors that gradually grew in the retroperitoneal space again. Therefore, we performed resection of newly recurrent tumors along with the right kidney, Gerota's fascia, diaphragm, and lumbar quadrate muscle for R0 resection. Pathological findings revealed recurrence of the past colon cancer with extensive lymphatic invasion. The recurrent tumor had grown in a retroperitoneal space that was not covered in the primary surgical procedure. Therefore, this is considered a rare case of retroperitoneal metastasis.