Surgery for T4 rectal cancer- is treatment planning based on response MRI safe?

Abstract Introduction There is no clear consensus on using the response-MRI as opposed to the pretreatment-MRI for surgical planning in cT4 low rectal cancer. Methods Retrospective review of a database of abdominoperineal resections conducted at a single tertiary cancer center. Patients divided into 2 groups- Group A (clinical T3 and mesorectal fascia positive) and Group B (clinical T4) with the primary outcome being rate of pathological circumferential resection margin positivity. After propensity score matching, factors influencing pathological circumferential resection margin positivity were analysed using logistic regression. Results There were 237 patients in Group A and 127 in Group B, in the unmatched cohort, with a significantly higher number of females (43.3% vs 28.7%, p=0.005 ) and anterior circumferential resection margin positivity (68.5% vs 49%, p<0.001 ), with a lower number of patients receiving neoadjuvant chemotherapy in Group B (38.6% vs 49.8%, p=0.041 ). After propensity matching baseline characters were comparable. There was a higher percentage of extended-Total Mesorectal Excisions in group B (58.5% Vs 40.5%, p=0.004 ). The rate of pathological circumferential positivity was comparable in both groups (20/168 in Group A{11.9%} Vs 13/107 in Group B{12.1%}, p=0.951 ) with no impact of group on circumferential resection margin positivity on univariate (OR 1.023, p=0.951 ) or multivariate regression (OR 0.993, p=0.987). Both the DFS (median DFS 39 months Vs 54 months, p=0.970 ) and OS (3-year OS 72% Vs 67%, p=0.798 ) were comparable between groups. Conclusion For T4 low rectal cancers, post-treatment MRI can be used for surgical planning without any detriment in outcomes.