Tumor stage in patients operated for rectal cancer: a comparison of the pre-operative MR and the resection specimen, with specific attention to the effect of neo-adjuvant radiotherapy.

BACKGROUND

Evaluate the preoperative TN stage with MR and the postoperative stage with histology.

METHODS

Patients diagnosed with rectal cancer (2002-2015) and a pre-operative MR were included. A chart review was done. Pathology reports were evaluated for the post-operative tumor stage. Down staging was defined as a lower disease stage in the resection specimen compared with the pre-operative MR. Upgrading ("progression") was defined as a higher disease stage in the resection specimen. The study was approved by ethical committee of the Zaans Medisch Centrum.

RESULTS

From 176 out of 231 operated patients a pre-operative MR was available for evaluation. 142 patients (80.7%) underwent neo-adjuvant treatment; the remainder 19.3% underwent immediate surgery. Neo-adjuvant therapy resulted in significant down staging. However, almost 14% of patients had a higher TN stage as determined by the pre-operative MR. In patients who underwent immediate surgery the percentage with "progression" was 30%. The number of patients with stage 1 and 2 were higher in the group not treated with neo-adjuvant therapy. There was no significant difference in tumor stage as determined by histological examination of the resection specimen.

CONCLUSIONS

The diagnostic accuracy of the MR is not perfect. Underestimation as well as overestimation of the tumor occurred both in the patients treated with radiotherapy as well as those who underwent immediate operation. As such, MR results should be interpreted with caution when devising a treatment strategy.