A 65-year-old woman presents with left-sided lower abdominal pain, iron-deficiency anaemia and a palpable mass in the left iliac fossa. What is the most likely cause?

Choose one answer.

1. AStricturing Crohn's disease
2. BCarcinoma of the sigmoid (left) colon
3. CA complicated diverticular mass
4. DA tubo-ovarian mass
5. EToxic megacolon

Show answer and explanation

Answer: B. Carcinoma of the sigmoid (left) colon

Left-sided colorectal carcinoma

Left-sided (descending/sigmoid) colon cancer commonly presents with left-sided abdominal pain, anaemia and a palpable mass, and with altered bowel habit and obstruction because the left colon has a narrower lumen and more solid stool.

Right versus left colon cancer

Side	Typical presentation
Right (caecum/ascending)	Iron-deficiency anaemia, vague pain, mass; obstruction is late (wide lumen, liquid stool)
Left (descending/sigmoid)	Altered bowel habit, obstruction, PR bleeding, mass; annular 'apple-core' tumours

Why this matters

• Recognising the side-specific pattern guides investigation; any change in bowel habit, PR bleeding or iron-deficiency anaemia in an older adult warrants colonic evaluation.