On the Additional Information Provided by 3T-MRI ADC in Predicting Tumor Cellularity and Microscopic Behavior

Simple Summary

Breast cancer is the most common cancer in women worldwide. Increasing knowledge of the microscopic behavior of tumors has allowed for personalized and increasingly effective therapies. Biopsy is the first step in the histological evaluation of breast cancer. However, biopsy may only be partially representative of the entire tumor. The only currently recognized independent histological prognostic factor is grading, an expression of replicative cellular behavior. However, other factors such as the Ki-67 proliferation index and tumor cellularity provide additional information on tumor aggressiveness. MRI is the imaging technique routinely used in the loco-regional tumor staging phase. Currently, the MRI protocol includes DWI sequences. DWI is an expression of the restriction of water molecules and can be quantified through ADC values. In our work, entitled "On the additional information provided by 3T-MRI ADC in predicting tumor cellularity and microscopic behavior ", we aim to demonstrate how ADC can significantly correlate with these histological factors, in particular with the cellularity obtained in the definitive histological sample compared to the biopsy sample; ADC values may therefore offer a valuable support for biological evaluation in the pre-surgical phase.

Background: to evaluate whether Apparent Diffusion Coefficient (ADC) values of invasive breast cancer, provided by 3T Diffusion Weighted-Images (DWI), may represent a non-invasive predictor of pathophysiologic tumor aggressiveness. Methods: 100 Patients with histologically proven invasive breast cancers who underwent a 3T-MRI examination were included in the study. All MRI examinations included dynamic contrast-enhanced and DWI/ADC sequences. ADC value were calculated for each lesion. Tumor grade was determined according to the Nottingham Grading System, and immuno-histochemical analysis was performed to assess molecular receptors, cellularity rate, on both biopsy and surgical specimens, and proliferation rate (Ki-67 index). Spearman's Rho test was used to correlate ADC values with histological (grading, Ki-67 index and cellularity) and MRI features. ADC values were compared among the different grading (G1, G2, G3), Ki-67 (20%) and cellularity groups (< 50%, 50-70% and > 70%), using Mann-Whitney and Kruskal-Wallis tests. ROC curves were performed to demonstrate the accuracy of the ADC values in predicting the grading, Ki-67 index and cellularity groups. Results: ADC values correlated significantly with grading, ER receptor status, Ki-67 index and cellularity rates. ADC values were significantly higher for G1 compared with G2 and for G1 compared with G3 and for Ki-67 < 20% than Ki-67 > 20%. The Kruskal-Wallis test showed that ADC values were significantly different among the three grading groups, the three biopsy cellularity groups and the three surgical cellularity groups. The best ROC curves were obtained for the G3 group (AUC of 0.720), for G2 + G3 (AUC of 0.835), for Ki-67 > 20% (AUC of 0.679) and for surgical cellularity rate > 70% (AUC of 0.805). Conclusions: 3T-DWI ADC is a direct predictor of cellular aggressiveness and proliferation in invasive breast carcinoma, and can be used as a supporting non-invasive factor to characterize macroscopic lesion behavior especially before surgery.