title: Locally advanced rectal cancer: histopathological correlation and predictive accuracy of serial MRI after neoadjuvant chemotherapy.
abstract: The accuracy of MRI after long-course chemoradiotherapy (CRT) in locally advanced rectal cancer (LARC) has been questioned. We have evaluated our experience of sequential MRI to assess pre-operative downstaging with histopathology correlation. 17 patients with LARC had three MRI scans: MRI 1, before treatment; MRI 2, 6 weeks post-CRT; and MRI 3, pre-operatively. MRI T and N staging were reported, with T3 subdivided into T3a (<5 mm through wall), T3b (1-5 mm), T3c (5-15 mm) and T3d (>15 mm). The maximal wall measurements and a prediction of vascular involvement were also correlated with histopathology. Histopathological agreement with MRI 3 was high: T 82%; N 88% and vascular 73%. Statistically significant (p<0.01) T downstaging was shown in MRI 2 and MRI 3 groups. In the 6 weeks post-CRT scan, T downstaging occurred in 6% of patients, with a further 29.4% showing T3c to T3b downsizing. 41% showed N stage improvement. In the third MRI group pre-surgery, 41.2% showed an MRI T stage improvement, with a further T3 downsizing in 17.6% of patients. 50% of these responders had shown no T stage improvement on their second scan. The sequential scans also showed significant reduction in wall thickness (p<0.01). In conclusion, the pre-operative MRI showed ongoing response to CRT up to 12 weeks post-CRT, which has important clinical implications regarding the most appropriate time to operate. Improved agreement between MRI 3 and histopathology compared with previous studies including only one post-treatment MRI was also demonstrated.
authors.affiliation: Department of Radiology, Colchester General Hospital, Colchester CO4 5JL, UK. dianefjohnston@btinternet.com
authors.forename: D F
authors.initials: DF
authors.lastname: Johnston
authors.forename: K M
authors.initials: KM
authors.lastname: Lawrence
authors.forename: B F
authors.initials: BF
authors.lastname: Sizer
authors.forename: T H A
authors.initials: TH
authors.lastname: Arulampalam
authors.forename: R W
authors.initials: RW
authors.lastname: Motson
authors.forename: E
authors.initials: E
authors.lastname: Dove
authors.forename: N
authors.initials: N
authors.lastname: Lacey