RESUMEN
Primary umbilical tumours are extremely rare. We report primary serous adenocarcinoma arising from the coelomic mesothelium of the hernial sac. A 60-year-old woman presented with an umbilical swelling of six months duration that became painful in the last three days. Examination revealed a tender umbilical swelling diagnosed as obstructive hernia that needed surgery. When dissecting the sac during surgery, a small subcutaneous abscess was encountered. The sac contained an omentum with a hard nodule at the surface which was excised. Umbilical hernia repair was performed. Histology of the omental nodule revealed serous papillary adenocarcinoma. Chest and abdomen computed tomography, pelvic magnetic resonance imaging, gastroscopy, colonoscopy and laparotomy did not reveal the primary site of the tumour.