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.