The Apparent Diffusion Coefficient (ADC) is a useful biomarker in predicting metastatic colon cancer using the ADC-value of the primary tumor

Abstract

Purpose: To investigate the role of the apparent diffusion coefficient (ADC) as a potential imaging biomarker to predict metastasis (lymph node metastasis and distant metastasis) in colon cancer based on the ADC-value of the primary tumor.

Methods: Thirty patients (21M, 9F) were included retrospectively. All patients received a 1.5T MRI of the colon including T2 and DWI sequences. ADC maps were calculated for each patient. An expert reader manually delineated all colon tumors to measure mean ADC and histogram metrics (mean, min, max, median, standard deviation (SD), skewness, kurtosis, 5th-95th percentiles) were calculated. Advanced colon cancer was defined as lymph node mestastasis (N+) or distant metastasis (M+). The student Mann Whitney U-test was used to assess the differences between the ADC means of early and advanced colon cancer. To compare the accuracy of lymph node metastasis (N+) prediction based on morpholigical criteria versus ADC-value of the primary tumor, two blinded readers, determined the lymph node metastasis (N0 vs N+) based on morphological criteria. The sensitivity and specificity in predicting lymph node metastasis was calculated for both readers and for the ADC-value of the primary tumor, with histopathology results as the gold standard.

Results: There was a significant difference between the mean ADC-value of advanced versus early tumors (p = 0.002). The optimal cut off value was 1179 * 10-3 mm2/s with an area under the curve (AUC) of 0.83 and a sensitivity and specificity of 81% and 86% respectively to predict advanced tumors. Histogram analyses did not add any significant additional value. The sensitivity and specificity for the prediction of lymph node metastasis based on morphological criteria were 40% and 63% for reader 1 and 30% and 88% for reader 2 respectively. The primary tumor ADC-value using 1.179 * 10-3 mm2/s as threshold had a 100% sensitivity and specificity in predicting lymph node metastasis.

Conclusion: The ADC-value of the primary tumor has the potential to predict advanced colon cancer, defined as lymph node metastasis or distant metastasis, with lower ADC values significantly associated with advanced tumors. Furthermore the ADC-value of the primary tumor increases the prediction accuracy of lymph node metastasis compared with morphological criteria.

Fig 1. Boxplots for the mean ADC value for early and advanced tumors.

ADC values given in mm²/s x 10⁻³. ADC = apparent diffusion coefficient.

Fig 2. ROC curve for optimal cut of value.

Optimal cut off value receiver operating characteristic (ROC) curve of the mean ADC with an area under the curve (AUC) of 0.83.

Fig 3. Example of image processing.

The T2 weighted MRI sequence (top picture) is showing the tumor in the sigmoid colon (arrow). The middle picture is the corresponding b1000 weighted DWI (Diffusion Weighted Imaging) sequence showing a high signal intensity within the tumor (consistent with malignancy). Bottom picture shows an example of tumor delineation on the corresponding ADC (Apparent Diffusion Coefficient) as performed to obtain the mean ADC-value of the whole tumor. An abdominal radiologist with 13 years experience in reading abdominal MRI and a radiology resident delineated each tumor in consensus directly on the ADC map whilst referring to the T2 weighted images (top) and the DWI sequence (middle) for anatomical reference.