Amide proton transfer imaging to predict tumor response to neoadjuvant chemotherapy in locally advanced rectal cancer

Background and Aim The amount of proteins and peptides can be estimated with amide proton transfer (APT) imaging. Previous studies demonstrated the usefulness of APT imaging to predict tumor malignancy. We determined whether APT imaging can predict the tumor response to neoadjuvant chemotherapy (NAC) in patients with locally advanced rectal cancer (LARC). Methods Seventeen patients with LARC who underwent a pretherapeutic magnetic resonance examination including APT imaging and NAC (at least two courses) were enrolled. The APT-weighted imaging (WI) signal intensity (SI) (%) was defined as magnetization transfer ratio asymmetry (MTRasym) at the offset of 3.5 ppm. Each tumor was histologically evaluated for the degree of degeneration and necrosis and then classified as one of five histological Grades (0, none; 1a, less than 1/3; 1b, 1/3 to 2/3; 2, more than 2/3; 3, all). We compared the mean APTWI SIs of the tumors between the Grade 0/1a/1b (low-response group) and Grade 2/3 (high-response group) by Student's t-test. We used receiver operating characteristics curves to determine the diagnostic performance of the APTWI SI for predicting the tumor response. Results The mean APTWI SI of the low-response group (n = 12; 3.05 +/- 1.61%) was significantly higher than that of the high-response group (n = 5; 1.14 +/- 1.13%) (P = 0.029). The area under the curve for predicting the tumor response using the APTWI SI was 0.87. When >= 2.75% was used as an indicator of low-response status, 75% sensitivity and 100% specificity of the APTWI SI were obtained. Conclusion Pretherapeutic APT imaging can predict the tumor response to NAC in patients with LARC.