26th April 2024

A 57-year-old man presents with a 6-month history of alternating constipation and diarrhoea, recent unexplained weight loss, and persistent abdominal discomfort.

A 57-year-old man presents with a 6-month history of alternating constipation and diarrhoea, recent unexplained weight loss, and persistent abdominal discomfort. He also reports noticing blood mixed with his stool. He has no significant past medical history and takes no regular medications.

Investigations:

Haemoglobin: 98 g/L (130–180)

White cell count: 11.2 × 10^9/L (4.0–11.0)

Platelets: 420 × 10^9/L (150–400)

Carcinoembryonic antigen (CEA): Elevated

Which is the most likely diagnosis?