Breast MRI for prediction of lymphovascular invasion in breast cancer patients with clinically negative axillary lymph nodes.

Objective: To retrospectively assess magnetic resonance imaging (MRI) findings that can predict lymphovascular invasion (LVI) in invasive breast cancer patients who were diagnosed with clinically negative axillary lymph nodes (LNs) preoperatively.

Methods: This study included 140 lesions of 140 patients who underwent preoperative breast MRI and breast surgery, with omission of axillary LN dissection. Clinical characteristics and MRI findings were evaluated. The T2 signal intensity (SI) ratio (mean T2 SI of the tumor/mean T2 SI of the muscle), tumor apparent diffusion coefficient (ADC) value, peritumoral ADC value, peritumor-tumor ADC ratio (peritumoral maximum ADC value/tumor mean ADC value), and ADC value of the contralateral breast parenchyma were retrospectively assessed. Statistical analyses were performed to identify significant factors for predicting LVI. Inter-observer variability was calculated.

Results: The tumor ADC value (all ages: p = 0.005; age ≤ 55: p < 0.001), peritumoral ADC value (age ≤ 55: p = 0.04), and peritumor-tumor ADC ratio (all ages: p < 0.001; age ≤ 55: p < 0.001) were significantly associated with LVI on univariate analysis. Multivariate logistic regression analysis revealed significant differences in the pathological size of the invasive component and the tumor ADC value for predicting LVI (odds ratio [OR]: 3.43; 95% confidence interval [CI]: 1.41-8.32; p = 0.007; OR: 16.0; 95% CI: 1.89-136; p = 0.01, respectively). Inter-observer agreement was substantial for the tumor ADC value (intraclass correlation coefficient [ICC] = 0.77; 95% CI: 0.70-0.83) and the ADC value of the contralateral breast parenchyma (ICC = 0.68; 95% CI: 0.59-0.76). There was moderate agreement for the peritumoral ADC value (ICC = 0.53; 95% CI: 0.40-0.64) and the peritumor-tumor ADC ratio (ICC = 0.49; 95% CI: 0.35-0.61) and fair agreement for the T2 SI ratio (ICC = 0.30; 95% CI: 0.15-0.45).

Conclusion: We found that the tumor ADC value, peritumoral ADC value, and peritumor-tumor ADC ratio were predictive MRI findings for LVI in patients aged ≤55. The tumor ADC value was the most significant predictor for LVI; moreover, inter-observer agreement for the tumor ADC value was substantial between two blinded observers with differences in interpretation experience.