Value of diffusion-weighted imaging for assessing site-specific response of advanced ovarian cancer to neoadjuvant chemotherapy: correlation of apparent diffusion coefficients with epithelial and stromal densities on histology.

This study correlates apparent diffusion coefficients (ADCs) from Diffusion-weighted Imaging (DWI) in primary ovarian tumours and their omental metastases following neoadjuvant chemotherapy with epithelial and stromal densities in order to relate them to histological composition. Eight patients underwent DWI at 1.5 T with four b-values (0, 600, 900, and 1,050 s/mm(2))at baseline and after one and three cycles of platinum-based chemotherapy. Mean ADCs were calculated at each timepoint from solid tumour at ovarian and omental sites. Specimens from 15 corresponding lesions (8 ovarian, 7 omental), obtained at interval debulking surgery, were stained immunohistochemically to quantify epithelial and stromal components. End-of-treatment ADC was correlated with epithelial and stromal densities. Longitudinal changes in ADC with treatment were compared between primary and metastatic lesions using parametric tests. No baseline differences in ADC between primary and metastatic sites were seen. Mean ADC increased significantly from baseline after both first and third cycle (P < 0.001) in both ovarian and omental lesions. ADC and total epithelial plus stromal density (lesion cellularity) were negatively correlated in ovarian lesions (r= -0.79, P=0.02) but not in omental metastases or when both sites were considered together. However, ADC and epithelial density were negatively correlated in ovarian (r=- 0.78, P=0.02) and omental lesions (r=-0.75, P=0.04) and when both sites were considered together (r=-0.77, P< 0.001). There was no significant correlation between ADC and stromal density. Thus ADC reflects mainly epithelial content in advanced ovarian cancer and is not solely a function of lesion cellularity.