Combined carcinoid-adenocarcinoma tumour of the anal canal.

The concurrence of carcinoid admixed with adenocarcinoma in the gastrointestinal tract is an unusual phenomenon that has been reported in the oesophagus, stomach, small intestine, appendix, colon and rectum. These mixed or 'composite' tumours seem to be derived from a multipotential stem cell capable of bidirectional differentiation and have a worse prognosis than ordinary adenocarcinoma. Chromogranin-A staining has increased the diagnostic yield for detecting these tumours and provides information for perioperative management and long-term prognosis. We describe a patient who presented to our department due to painful defecation. Sigmoidoscopy demonstrated a mass in the anal canal. Histology revealed that the tumour was a mixed carcinoid-adenocarcinoma neoplasm. To our knowledge, this is the first report in the English literature of a composite tumour of the anal canal.