The additional utility of apparent diffusion coefficient values of clear-cell renal cell carcinoma for predicting metastasis during clinical staging.

Background: The apparent diffusion coefficient (ADC) value is known to be an indicator of tumor activity. The ADC value of high-grade clear-cell renal cell carcinoma (RCC) is significantly lower than that of low-grade clear-cell RCC.

Purpose: To investigate the utility of ADC values of clear-cell RCC by comparing ADC values between groups with T1a RCC (tumor size ≤ 4 cm) without metastasis and the group with metastasis.

Material And Methods: A retrospective review was performed on 51 patients with 51 RCCs who underwent 1.5 T magnetic resonance imaging (MRI) for evaluating a renal mass confirmed pathologically to be clear-cell RCC between January 2010 and August 2014. We compared ADC values between group A (T1a RCC without metastasis, T1aN0M0) and group B (RCC with metastasis) using the Mann-Whitney test.

Results: The patients were divided into group A (n = 30; tumor size: median, 24.5 mm; range, 8-40 mm; ADC value [×10 mm/s]: median, 1.71; range, 1.23-2.24) and group B (n = 21; tumor size: median, 87.5 mm; range, 18-150 mm; ADC value [×10 mm/s]: median, 1.35; range, 0.91-1.94). The ADC value differed significantly between the two groups. The area under the receiver operating characteristic curve was 0.869. Using the optimum cutoff value (1.552 × 10 mm/s), ADC had a sensitivity of 80.0% and specificity of 81.0%.

Conclusion: There was a statistically significant difference in the ADC between group A (T1a clear-cell RCC without distant metastasis) and group B (advanced clear-cell RCC with lymph node metastasis or distant metastasis).