CRM Rectal Cancer MRI — SCE Medical Oncology MCQ

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ModerateGI CancersCRM Rectal Cancer MRISCE Medical Oncology

A 65-year-old man with locally advanced rectal cancer has a circumferential resection margin (CRM) involvement predicted on MRI. Why is CRM the most important MRI measurement in rectal cancer?

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Correct answer: B — A threatened/involved CRM (<1 mm from tumour to mesorectal fascia) on MRI is the strongest predictor of local recurrence and survival — it determines neoadjuvant treatment intensity and surgical approach

CRM is the distance from the deepest tumour/involved lymph node to the mesorectal fascia (the surgical resection plane in TME). MRI CRM <1 mm predicts a high risk of positive surgical CRM and local recurrence. It is the most important single measurement guiding: (1) neoadjuvant treatment intensity (CRM-threatened → intensive CRT or TNT), (2) surgical approach (CRM-involved posteriorly may require extended resection), (3) prognosis. The MERCURY study validated MRI CRM prediction accuracy (within 0.5 mm of pathological CRM).

Reference: NICE NG151; MERCURY Study; ESMO 2024 Rectal Cancer