What is the most common site of origin for colorectal carcinoma in India?

Question

Accepted Answer

A. Rectosigmoid junction and rectum. ## Most Common Site of Colorectal Carcinoma

### Epidemiology

**Key Point:** The rectosigmoid region (rectum and sigmoid colon) accounts for approximately 60–70% of all colorectal carcinomas worldwide, including in India.

### Anatomical Distribution

| Site | Frequency | Remarks |
| --- | --- | --- |
| Rectosigmoid (rectum + sigmoid) | 60–70% | Most common; easier to detect on digital rectal exam |
| Cecum and ascending colon | 15–20% | Right-sided lesions; often diagnosed late |
| Transverse colon | 5–10% | Uncommon |
| Descending colon | 5–10% | Uncommon |

### Why Rectosigmoid is Most Common

1. **Anatomical factors:** The rectosigmoid has the smallest luminal diameter, predisposing to stricture formation and obstruction.
2. **Stasis and exposure:** Fecal stasis in the sigmoid colon prolongs contact with carcinogens.
3. **Mucosa type:** The rectosigmoid mucosa may have heightened susceptibility to malignant transformation.

### Clinical Pearl

**High-Yield:** Rectal cancers are more amenable to early detection via digital rectal examination (DRE) and sigmoidoscopy, which is why they are often diagnosed at earlier stages compared to right-sided lesions. However, left-sided (rectosigmoid) cancers still represent the bulk of CRC burden.

### Implications for Screening

- **Sigmoidoscopy** is effective for detecting rectosigmoid lesions.
- **Colonoscopy** is the gold standard for visualizing the entire colon and detecting proximal lesions.
- **Fecal occult blood test (FOBT)** is useful as a screening tool in asymptomatic populations.

Answer

B. Descending colon

Answer

C. Transverse colon

Answer

D. Cecum and ascending colon

What is the most common site of origin for colorectal carcinoma in India?

Explanation

Most Common Site of Colorectal Carcinoma

Epidemiology

Anatomical Distribution

Why Rectosigmoid is Most Common

Clinical Pearl

Implications for Screening

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Site	Frequency	Remarks
Rectosigmoid (rectum + sigmoid)	60–70%	Most common; easier to detect on digital rectal exam
Cecum and ascending colon	15–20%	Right-sided lesions; often diagnosed late
Transverse colon	5–10%	Uncommon
Descending colon	5–10%	Uncommon