## Most Common Site of Colorectal Adenocarcinoma **Key Point:** The rectosigmoid region (rectum and sigmoid colon combined) is the most common site for primary adenocarcinoma of the colon, accounting for approximately 50–60% of all colorectal cancers. ### Distribution of Colorectal Cancer by Site | Site | Frequency (%) | |------|---------------| | Rectosigmoid | 50–60 | | Cecum | 10–15 | | Ascending colon | 5–10 | | Transverse colon | 5–10 | | Descending colon | 5–10 | ### Why Rectosigmoid? - **Prolonged fecal stasis:** Increased contact time between carcinogens and mucosa - **Lymphoid tissue concentration:** Higher density of GALT in this region - **Anatomical narrowing:** Smaller luminal diameter increases pressure and contact **Clinical Pearl:** Rectosigmoid cancers are more accessible to sigmoidoscopy and colonoscopy, making early detection feasible. **High-Yield:** Always perform full colonoscopy in suspected colorectal cancer to rule out synchronous lesions, as 3–5% of patients have multiple primary tumors.
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