Extramural depth of tumor invasion at thin-section MR in rectal cancer: associating with prognostic factors and ADC value

Purpose: To assess the value of maximal extramural depth (EMD) of T3 tumor spread on MRI as a potential noninvasive imaging biomarker of tumor aggressiveness in rectal cancer, by analyzing the relationship between tumoral EMD values and clinical or histological prognostic parameters. In addition, we try to investigate the relationship between EMD and apparent diffusion coefficient (ADC) values.

Materials and methods: Ninety rectal cancer patients who underwent primary MRI staging and diffusion weighted imaging (DWI) as T3 tumor were included. Tumor EMD was measured, and the EMD values of the subgroups based on pretreatment CEA, CA19-9 levels, N stage, and histological parameters were compared. The correlation between EMD and ADC values was compared.

Results: Interobserver agreement of confidence levels for observers 1 and 2 was good for cN stage (k = 0.678) and EMD measurement(k = 0.612) and was excellent for ADC measurement (k = 0.880). Tumor EMDs differ between CEA <5 ng/mL versus ≥ 5 ng/mL (P = 0.013), CA19-9 < 27 U/mL versus ≥ 27 U/mL (P = 0.012), the groups of cN0 versus cN+ cancers (P = 0.049), and between the several groups of histological differentiation grades (P = 0.033). There was no significant difference in EMDs between the various groups of vessel carcinoma embolus and neural invasion. A significant negative correlation (r = -0.581; P = 0.001) between ADC and EMD values was found.

Conclusion: Significant correlations were found between EMD values and CEA, CA19-9 level, differentiation grade and ADC value. As been found, higher EMD values were associated with a more aggressive tumor profile and, therefore, EMD has the potential to become an imaging biomarker of tumor aggressiveness indicator.