## Why Colonoscopy every 10 years as per standard ACS 2018 guidelines is right The patient presents with classic LEFT-sided colorectal adenocarcinoma (sigmoid location with hematochezia, pencil-thin stools, and change in bowel habit). The structure marked **A** (invasive atypical glands) represents the malignant epithelium that develops via the adenoma-carcinoma sequence over 10–15 years. Per ACS 2018 guidelines, the screening age was lowered from 50 to 45 years for average-risk individuals, and colonoscopy every 10 years remains the gold standard screening modality. This patient, if screened appropriately at age 45, would have had the opportunity for early detection and prevention through adenoma removal before progression to invasive carcinoma (marked **A**). ## Why each distractor is wrong - **Annual FIT or multitarget stool DNA every 3 years**: While these are acceptable alternative screening modalities per ACS 2018, they are not the gold standard. Colonoscopy every 10 years is the preferred first-line recommendation for average-risk individuals starting at age 45. - **Flexible sigmoidoscopy annually until age 75**: Sigmoidoscopy is no longer recommended as a primary screening tool in current guidelines. It visualizes only the distal colon and misses proximal lesions; colonoscopy is superior. - **CT colonography every 5 years as the primary screening modality**: CT colonography is an acceptable alternative for those who decline colonoscopy, but it is not the primary or most appropriate first-line screening recommendation per ACS 2018. **High-Yield:** ACS 2018 lowered CRC screening start age to 45 years; colonoscopy every 10 years is the gold standard. Left-sided CRC (sigmoid/rectum) presents with hematochezia and obstruction; right-sided presents with iron deficiency anemia and occult bleeding. [cite: Robbins 10e Ch 17; Harrison 21e Ch 80; American Cancer Society 2018 Colorectal Cancer Screening Guidelines]
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