Diffusion‐weighted MRI in rectal cancer: Apparent diffusion coefficient as a potential noninvasive marker of tumor aggressiveness

Purpose: To assess the value of diffusion‐weighted MR imaging (DWI) as a potential noninvasive marker of tumor aggressiveness in rectal cancer, by analyzing the relationship between tumoral apparent diffusion coefficient (ADC) values and MRI and histological prognostic parameters. Materials and Methods: Fifty rectal cancer patients underwent primary staging MRI including DWI before surgery and neo‐adjuvant therapy. In 47, surgery was preceded by short‐course radiation therapy (n = 28) or long‐course chemoradiation therapy (n = 19). Mean tumor ADC was measured and compared between subgroups based on pretreatment CEA levels, MRI parameters (mesorectal fascia ‐ MRF ‐ status; T‐stage; N‐stage) and histological parameters (differentiation grade: poorly differentiated, poorly moderately differentiated, moderately differentiated, moderately well differentiated, well‐differentiated; lymphangiovascular invasion). Results: Mean tumor ADCs differ between MRF‐free versus MRF‐invaded tumors ( P = 0.013), the groups of cN0 versus cN+ cancers ( P = 0.011), and between the several groups of histological differentiation grades ( P = 0.025). There was no significant difference in mean ADCs between the various groups of CEA levels, the T stage, and the presence of lymphangiovascular invasion. Conclusion: Lower ADC values were associated with a more aggressive tumor profile. Significant correlations were found between mean ADC values and radiological MRF status, N stage and differentiation grade. ADC has the potential to become an imaging biomarker of tumor aggressiveness profile. J. Magn. Reson. Imaging 2012;35:1365–1371. © 2012 Wiley Periodicals, Inc.