Extended TME in Locally Advanced Rectal Cancer (T4a) and the clinical role of MRI evaluated neo-adjuvant downstaging

Objective: To evaluate the clinical ability of MRI taken before and after neoadjuvant treatment of locally advanced rectal cancer (LARC) to predict the necessary extension of the TME procedure, the surgical outcome and to evaluated the use of histopathological tumor regression grade (TRG). Methods: From 2002 until 2007, 92 patients with MRI evaluated T4a primary rectal cancer all treated with neoadjuvant treatment and elective surgery was included in a prospective study at the tertiary referral center The Radiumhospitalet Cancer Center. Results: Extended TME was performed in 95% of the patients and R0 resection was obtained in 80 %, R2 resection in three percent. Fifty-five percent had at histopathological examination a T downstaging not detected by yMRI which had predicted only ten percent downstaging after neoadjuvant treatment. N-staging by MRI after neo-adjuvant treatment and final histopathology was similar in 51 % of the cases. Ten percent was evaluated histopathological as TRG1, 60 % as TRG 2-3 and 30 % as TRG 4-5. Preoperative CRT resulted in a higher percent of TRG1-3 compared to patients receiving only RT. Conclusion: MRI identifies patients in need of neo-adjuvant treatment, but did not predict downstaging after neoadjuvant treatment satisfactorily. In 55 % of the ypT4 patients scattered tumour cells were remaining within areas of fibrosis (TRG2-3). Therefore, to achieve a surgical result with a safe margin an extended TME surgery should be performed in accordance with pre-treatment MRI. The study has initiated a new approach to histopathological classification where we introduce a MRI assisted technique for investigating areas at risk outside the mesorectal fascia in the removed specimen