MRI predictive factors for tumor response in rectal cancer following neoadjuvant chemoradiation therapy--implications for induction chemotherapy?
OBJECTIVE
Clinical and magnetic resonance imaging (MRI) characteristics at baseline and following chemoradiation therapy (CRT) most strongly associated with histopathologic response were investigated and survival outcomes evaluated in accordance with imaging and pathological response.


METHODS
Responders were defined as mrT3c/d-4 downstaged to ypT0-2 on pathology or low at risk mrT2 downstaged to ypT1 or T0. Multivariate logistic regression of baseline and posttreatment MRI: T, N, extramural venous invasion (EMVI), circumferential resection margin, craniocaudal length <5 cm, and MRI tumor height ≤5 cm were used to identify independent predictor(s) for response. An association between induction chemotherapy and EMVI status was analyzed. Survival outcomes for pathologic and MRI responders and nonresponders were analyzed.


RESULTS
Two hundred eighty-one patients were eligible; 114 (41%) patients were pathology responders. Baseline MRI negative EMVI (odds ratio 2.94, P=.007), tumor height ≤5 cm (OR 1.96, P=.02), and mrEMVI status change (positive to negative) following CRT (OR 3.09, P<.001) were the only predictors for response. There was a strong association detected between induction chemotherapy and ymrEMVI status change after CRT (OR 9.0, P<.003). ymrT0-2 gave a positive predictive value of 80% and OR of 9.1 for ypT0-2. ymrN stage accuracy of ypN stage was 75%. Three-year disease-free survival for pathology and MRI responders were similar at 80% and 79% and significantly better than poor responders.


CONCLUSIONS
Tumor height and mrEMVI status are more important than baseline size and stage of the tumor as predictors of response to CRT. Both MRI- and pathologic-defined responders have significantly improved survival. "Good response" to CRT in locally advanced rectal cancer with ypT0-2 carries significantly better 3-year overall survival and disease-free survival. Use of induction chemotherapy for improving mrEMVI status and knowledge of MRI predictive factors could be taken into account in the pursuit of individualized neoadjuvant treatments for patients with rectal cancer.
Radiotherapy Department, The Royal Marsden, Sutton/London, United Kingdom.
Stanley K T
SK
Yu
Diana
D
Tait
Ian
I
Chau
Gina
G
Brown
D000368:Aged; D000704:Analysis of Variance; D000970:Antineoplastic Agents / Q000627:therapeutic use; D059248:Chemoradiotherapy; D017024:Chemotherapy, Adjuvant / Q000379:methods; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D060828:Induction Chemotherapy; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy / Q000379:methods* / Q000401:mortality; D009361:Neoplasm Invasiveness / Q000473:pathology; D009367:Neoplasm Staging / Q000379:methods; D012004:Rectal Neoplasms / Q000401:mortality / Q000473:pathology* / Q000628:therapy*; D012044:Regression Analysis; D012189:Retrospective Studies; D016896:Treatment Outcome; D047368:Tumor Burden
D000970:Antineoplastic Agents