RESUMEN

The existence of both neuroendocrine and non-neuroendocrine histology in variable proportion in a lesion has been described by the World Health Organisation (WHO) as mixed neuroendocrine and non-neuroendocrine neoplasm (MiNEN). The pathogenesis of this tumour remains controversial but molecular studies point towards a common monoclonal origin. Tumours are classified as functioning and nonfunctioning based on substances secreted. The nonfunctioning tumours may be discovered due to its local effect. Presented is a 66-year-old male with an intra-abdominal mass, underwent laparotomy and excision biopsy with transient right lower limb lymphoedema. Histology confirmed retroperitoneal MiNEN with no evidence of tumour recurrence 12 months following surgery. MiNENs should be considered as a differential diagnosis in patients with intra-abdominal mass. Surgical resection is recommended as this may offer the best treatment option.