**Question:** Which among the following is the least common symptom of Wilms tumour?

A. Abdominal pain
B. Hematuria
C. Delayed development
D. Anorexia

**Core Concept:** Wilms tumor is a childhood kidney cancer that primarily affects children under the age of 5 years. It is characterized by the presence of three cell types: epithelial, stromal, and blastemal cells, and can be further classified based on its histopathology.

**Why the Correct Answer is Right:** Delayed development (option C) is the least common symptom of Wilms tumor because this symptom is more commonly associated with other conditions, such as genetic disorders or kidney dysfunction due to other causes. Wilms tumor usually presents with more prominent symptoms like abdominal pain, hematuria, and anorexia.

**Why Each Wrong Option is Incorrect:**

A. Abdominal pain (option A) is a more common symptom due to the tumor compressing surrounding organs, causing abdominal discomfort and swelling.
B. Hematuria (option B) is also common as the tumor can compress or invade the renal pelvis, ureter, or bladder, leading to blood in the urine.
D. Anorexia (option D) is another common symptom as the tumor may cause pain, compression, or dysfunction, leading to decreased appetite.

**Clinical Pearl/High-Yield Fact:** Wilms tumor typically presents with a triad of symptoms: abdominal mass (palpable or non-palpable), hemihypertrophy (unilateral enlargement of the affected kidney), and hematuria (blood in the urine). A high index of suspicion and appropriate investigations can lead to early diagnosis and better prognosis.

**Correct Answer:** C. Delayed development (option C) is the least common symptom of Wilms tumor, making it the correct answer. The other options (A, B, and D) are more common presentations due to the tumor's effects on kidney function, compression, or pain.