Multiple liver metastases originating from synchronous double cancer of neuroendocrine tumor and rectal cancer: a case report

BACKGROUND: Neuroendocrine tumor (NET) is a relatively rare tumor and can develop in almost any organ, but primary mesenteric NETs are extremely rare. In addition, liver metastases from synchronous double cancer of neuroendocrine tumor graded as G1 and second primary malignancies (SPMs) have never been reported before. We herein report a case of multiple liver metastases from synchronous double cancer of NET (G1) at the ileal mesentery and rectal cancer. CASE PRESENTATION: A 66-year-old man was identified as having tumors in the rectum and the ileal mesentery by computed tomography (CT). He underwent laparoscopic low anterior resection for rectal cancer and biopsy of the ileal mesentery lymph node and was diagnosed with rectal cancer as pT3 pN1 cM0 (stage IIIB) and NET (G1) of the ileal mesentery. He received oxaliplatin and capecitabine (XELOX) for 3 months as adjuvant chemotherapy for rectal cancer. The NET (G1) of the ileal mesentery was low grade and had not expanded at follow-up. A CT scan performed 4 years after the surgery indicated multiple liver metastases. All the metastases had the same findings on CT and magnetic resonance imaging (MRI). Thus, the patient underwent the first stage of modified associating liver partition and portal vein ligation for staged hepatectomy (modified ALPPS), comprising partial hepatectomies of segments 3 and 4, ligation of the right branch of portal vein, and hepatic partition on the demarcation line, followed by the second stage of modified ALPPS (right lobectomy). Histopathological findings revealed that the 14 nodules were metastatic liver tumors of rectal cancer and the 2 nodules were liver metastases of the NET (G1). CONCLUSIONS: Our findings suggest that synchronous double cancer of NET and gastrointestinal cancer may be indistinguishable in preoperative images. However, curative resection, precise pathological diagnosis, and adequately adjusted treatment may result in a better prognosis.