Assessment of aggressiveness of rectal cancer using 3-T MRI: correlation between the apparent diffusion coefficient as a potential imaging biomarker and histologic prognostic factors

Background Diffusion-weighted magnetic resonance imaging (DW-MRI) permits non-invasive assessment of tumor characteristics. Purpose To assess the value of DW-MRI as a potential non-invasive marker of tumor aggressiveness in rectal cancer by analyzing the relationship between tumoral apparent diffusion coefficient (ADC) values of MRI and histopathologic prognostic parameters that are not affected by preoperative chemoradiation therapy. Material and Methods Forty patients with rectal cancer were assessed with primary staging 3-T MRI, including DWI, before undergoing surgical therapy. In all patients, surgery was performed without neoadjuvant therapy. Mean tumor ADC was measured and compared between subgroups based on pretreatment carcinoembryonic antigen (CEA) levels, MRI parameters (e.g. postoperative local recurrence), and histopathologic parameters, including A (invasive distance: A1, T-stage; A2, mesorectal fascia [MRF] status), B (differentiation grade: B1, poorly differentiated; B2, moderately differentiated; B3, well differentiated), C (others: C1, N-stage; C2, lymphangiovascular invasion). Results Mean tumor ADCs were different when comparing groups stratified by histologic differentiation grades (P = 0.0192). There was no significant difference in mean ADCs when stratifying patients according to CEA levels, T-stage, N-stage, MRF status, presence of lymphangiovascular invasion, or the presence of local recurrence. Conclusion Significant correlations were found between mean ADC values and differentiation grade. ADC may be useful as an imaging biomarker of tumor aggressiveness, but it cannot serve as an independent biomarker of advanced rectal cancer.