Assessment of the inferior mesenteric vein diameter as a surrogate marker to evaluate response to neoadjuvant chemoradiotherapy for locally advanced rectal adenocarcinoma.

Aim: Neoadjuvant chemoradiotherapy for locally advanced rectal cancer aims to downstage prior to definitive management. Repeat imaging assessment of the tumour post-therapy has implications for treatment. Our aim was to assess if the inferior mesenteric vein (IMV) diameter measured on CT can be used as a surrogate marker for evaluation of tumour response to neoadjuvant treatment.
Method: IMV diameter was assessed in patients with and without locally advanced rectal cancer, pre- and post-radiotherapy, to ascertain if IMV diameter is a surrogate marker of tumour response.
Results: IMV diameter was 5.9 mm in patients with rectal cancer vs 4.7 mm in patients without (P = 0.0001). The baseline IMV diameter was significantly higher for cases with local lymphadenopathy [N0 5.2 mm vs N1/2 6 mm (P = 0.0059)] and extramural venous invasion (EMVI) [negative 5.4 mm vs positive 6.4 mm (P = 0.0001)]. Post-radiotherapy there was a significant decrease in the IMV diameter in cases with treatment response compared to non-responders: the percentage change in IMV diameter was a 17.54% decrease vs 1.39% increase (P = 0.0001). These results were reproduced on comparing between magnetic resonance tumour regression grades using ANOVA (P = 0.0001). There was also a significant decrease in IMV diameter when assessing lymph node (LN) and EMVI response vs non-responders (P = 0.0001 and 0.0001 respectively).
Conclusion: Patients with rectal cancer have a dilated IMV compared with patients without rectal cancer. We confirm that IMV diameter is a potential surrogate marker of LN status and EMVI at baseline. IMV diameter is also a marker of tumour, LN and EMVI response to chemoradiotherapy.
(Colorectal Disease © 2017 The Association of Coloproctology of Great Britain and Ireland.)