Locally advanced rectal cancer: MR imaging in prediction of response after preoperative chemotherapy and radiation therapy.
OBJECTIVE
To prospectively differentiate, at magnetic resonance (MR) imaging, patients with locally advanced nonmucinous rectal cancer who will respond to long-course chemotherapy and radiation therapy (CRT) from those who will not respond, with histopathologic results as the reference standard.


METHODS
Institutional review board approval for this study was obtained, and all patients provided written informed consent. High-spatial-resolution T2-weighted MR images were acquired before and 6-8 weeks after CRT in 53 patients (33 men, 20 women; mean age, 63 years; age range, 42-79 years). Patients were categorized as responders to CRT (patients with T3 cancer that converted to T2 or a lower stage, patients with T4 cancer that converted to T3 or a lower stage) or as nonresponders (patients with stable or progressive disease). At the posttreatment MR imaging examination, a decrease in signal intensity was considered to represent a morphologic response with fibrosis. Before CRT and surgery, tumor volume was calculated at MR imaging by multiplying cross-sectional area by section thickness. Tumor length was measured at MR imaging and in the histopathologic specimen. Nodal downstaging was evaluated. The relationship between pathologic response, morphologic MR imaging response, and percentage volume reduction was evaluated with the Mann-Whitney-Wilcoxon two-sample test.


RESULTS
Morphologic response assessment with MR imaging achieved a positive predictive value (PPV) of 84.2% (32 of 38) and a negative predictive value (NPV) of 66.7% (10 of 15). Volume reduction extent (> or = 70%) was significantly different between patients in whom disease was downstaged and those in whom it was not downstaged (P = .000005) and showed additional diagnostic value, with an overall accuracy of 86.8% (46 of 53). Presurgical MR imaging and histopathologic tumor length did not show a significant difference. MR imaging accuracy for lymph node (N) stage was 86.8% (46 of 53) on the basis of morphologic criteria.


CONCLUSIONS
After CRT, morphologic and volumetric evaluation at MR imaging had a high PPV and a low NPV for response assessment. The detection of small clusters of residual tumor cells within fibrosis remains a problem.


BACKGROUND
http://radiology.rsnajnls.org/cgi/content/full/250/3/730/DC1.
Barbaro
Brunella
B
Department of Bioimaging and Radiological Sciences, Catholic University, School of Medicine, Policlinico A. Gemelli, Largo Gemelli, 1, 00168 Rome, Italy. bbarbaro@rm.unicatt.it
Fiorucci
Cecilia
C
Tebala
Carmen
C
Valentini
Vincenzo
V
Gambacorta
Maria Antonietta
MA
Vecchio
Fabio Maria
FM
Rizzo
Gianluca
G
Coco
Claudio
C
Crucitti
Antonio
A
Ratto
Carlo
C
Bonomo
Lorenzo
L
D000328:Adult; D000368:Aged; D017024:Chemotherapy, Adjuvant / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care / Q000379:methods*; D011379:Prognosis; D018714:Radiotherapy, Adjuvant / Q000379:methods*; D012004:Rectal Neoplasms / Q000175:diagnosis* / Q000628:therapy*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome