Aim

To study prognostic significance of MRI identified tumour deposits(TD), EMVI, mesorectal nodes(LNM) and pelvic sidewall disease(PSW) in rectal cancer.

Methods

This IRB approved study was conducted on patients with stage IIA-IIIC rectal adenocarcinoma treated with neoadjuvant long course chemoradiotherapy(LCCRT) and TME type of surgery between 2012-2018. A radiologist blinded to outcome reviewed staging and re-staging MRI for TD, EMVI, LN and PSW. We studied agreement between four radiologists. We obtained outcome data from a prospectively maintained database. The prognostic significance of imaging findings was assessed.

Results

297(186 males) patients with a mean age of 47.3(SD14.4) years were included. Majority had T3(n=206) or T4(n=59) stage disease. The mean duration of follow up was 49.3+/-25 months(6.6-101 months). 5-year overall (OS) and disease-free survival (DFS) was 84% and 74% respectively. Staging and re-staging MRI had EMVI in 49.5% and 31.3%; TD in 47.5% and 31.6%; LNM in 61.1% and 38.1% and PSW in 11.4% and 6.1%. OS was adversely affected by EMVI, TD and PSW with the adjusted HR(aHR) of 3.32, 3.31, 3.27 for staging MRI and 2.99, 3.1, 2.81 for restaging MRI respectively, p<0.05. DFS was affected by EMVI(aHR=1.85, 2.33) and TD(aHR= 1.83, 2.19), p<0.05. Persistence of these findings after LCCRT led to worst outcome. Intra and inter observer agreement for EMVI, TD and LN was 0.789, 0.734, 0.406 and 0.449, 0.354, 0.376 respectively, p<0.001.

Conclusion

MRI identified TD, EMVI and PSW disease are independent poor prognostic indicators in rectal cancer patients. Interobserver agreement for these findings was moderate to fair.