Clinical impact of imaging for restaging rectal cancer after preoperative chemoradiation

Purpose: To determine the accuracy of different imaging techniques in predicting local staging and the circumferential resection margin (CRM) status of rectal cancers (RC) after preoperative chemoradiotherapy (CRT). Material and Methods: We prospectively assessed 132 patients with locally advanced mid-to-low RC using CT, MRI and endorectal ultrasound (ERUS). 93 patients were studied with both MRI and ERUS. Post-CRT local staging and infiltration of CRM were compared with histopathology. Results: The overall concordance rate between CT (n = 98) and histopathology findings was 33%. Because of these disappointing results, this part of the study was discontinued. Unfortunately, the accuracy of T staging was low also using MRI (35%) and ERUS (33%). Grouping mural stage into ypT≤3 and ypT4 categories imaging showed high specificity and negative predictive value (NPV); particularly MRI achieved 92% specificity and 95% NPV. The accuracy of N staging was 67% and 65% for ERUS and MRI, respectively; the corresponding NPV were 75% and 78%. The specificity and NPV for the CRM involvement were 80% and 96%, respectively, for MRI. Conclusion: Current imaging techniques are unreliable for RC restaging purposes after CRT, but are useful in predicting T≤ 3 RC and RC with negative nodes and CRM. These findings may be of clinical relevance for planning less invasive surgery.