Can CRM status on MRI predict survival in locally advanced rectal cancers: Experience from the Indian subcontinent.
e15167 Background: Neoadjuvant chemoradiation has become the standard approach for treatment of locally advanced rectal cancers. Magnetic Resonence Imaging (MRI) is the staging modality of choice in rectal carcinoma. Recent reports have studied the impact of MRI on local recurrence and survival both in treatment naïve and post treatment settings Methods: A retrospective analysis of prospective database was performed over a period of 1 year. All pretreatment patients with carcinoma of rectum were included in the study. The status of CRM on MRI was compared to that on the histopathology and as a predictor of recurrence and survival. For analysis, the MRI scans done for patients at presentation were labeled as MRIT. This included all patients irrespective of further treatment received. Patients who were treated with NACTRT had two MRI scans. The MRI at presentation in this subset of patients was labeled as MRI1 and the reassessment MRI after NACTRT was labeled as MRI2. Thus, MRI1 represented a subset of MRIT with locally advanced tumors treated with NACTRT. All the sets of MRI scans were analyzed separately for prediction of CRM involvement and for their effect on local recurrence and survival rates. Results: 221 patients were included with a median follow-up 30 months. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRIT, MRI1 and MRI2 to predict CRM status were 50%, 62.3%, 96.5%, 5.6% and 61.8%, 50%, 55%, 95%, 6% and 54.7% and 77.8%, 63.7%, 98%, 11%, 64.5% respectively. On multivariate analysis pathological positive margins alone predicted a poor overall survival (OS) whereas involved CRM on pathology and pretreatment MRI predicted poorer disease free survival and OS Conclusions: CRM status on pathology remains the most important prognostic factor to impact overall survival, disease free survival and local recurrence. CRM status on MRI at presentation alone has significant impact on disease free survival and local recurrence. Although MRI done after neoadjuvant treatment may not predict survival, it has a role in helping modify the surgical approach with a goal to achieve a negative CRM on pathology.