How Accurate Are Flexible Sigmoidoscopy and MRI in Restaging Rectal Cancer After Neoadjuvant Therapy?

Williams H, Omer DM, Verheij FS, et al. Accuracy of Flexible Sigmoidoscopy and MRI in Restaging Rectal Cancer after Neoadjuvant Therapy: A Secondary Analysis of the OPRA Randomized Clinical Trial. Ann Surg. October 2025.

The secondary analysis of the OPRA randomized clinical trial provides quantitative insight into how accurately flexible sigmoidoscopy (FS) and MRI can identify true tumor response (TR) after total neoadjuvant therapy (TNT) for locally advanced rectal cancer. 

Of 324 patients enrolled, 304 (94%) completed TNT and 277 were restaged with both FS and MRI at a median of 7 weeks post-treatment. Among 265 patients eligible for analysis, 52% achieved a TR, defined as sustained complete clinical response (cCR) for ≥2 years or pathologic complete response. FS demonstrated higher diagnostic accuracy than MRI (65% versus 60%), with greater sensitivity (96% versus 95%) and specificity (33% versus 23%). When FS and MRI results were combined, accuracy improved modestly to 67%, with a positive predictive value (PPV) of 62% and negative predictive value (NPV) of 82%.

Clinically, these data reveal that nearly half of patients (46%) had discordant findings between FS and MRI, emphasizing the complementary yet imperfect nature of these tools. FS was significantly better than MRI at correctly identifying true responders (p = 0.03).

In the watch-and-wait (WW) cohort of 196 patients (71% of the total), local regrowth occurred in 35%—predominantly within 2 years of restaging. 5-year disease-free survival was highest among patients classified as cCR by both FS and MRI (89.6%), followed by cCR/near-complete clinical response (nCR) (72.1%), nCR/nCR (68.9%), and any incomplete clinical response (iCR) (49.8%; p < 0.001). Patients with nCR/nCR status had the greatest local regrowth risk (59.3%).