Imaging of ovarian cancer and peritoneal metastases

Current and emerging techniques

Peritoneal metastases are often the first presentation of ovarian malignancy. The use of imaging to evaluate peritoneal disease in ovarian cancer is essential for patient stratification to receive either primary surgery or chemotherapy, and to determine therapeutic result. Standard CT, however, frequently fails to identify small sites of peritoneal spread. Moreover, it does not provide a quantitative index of disease response to cytotoxic therapy as it relies on macroscopic morphological changes in tumor volume, and does not reflect preceding molecular events in the microenvironment of the tumor.

In an article published in the July 2010 of Nature Reviews Clinical Oncology, Dr S Kyriazi of the Section of Magnetic Resonance, Cancer Research UK and EPSRC Cancer Imaging Center, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK and colleagues describe the emerging role of functional imaging techniques, such as radioimmunoscintigraphy, PET/CT, diffusion-weighted MRI, dynamic contrast-enhanced MRI, and magnetic resonance spectroscopy in the staging of ovarian cancer and assessing treatment response.

They wrote that CT and MRI use reduction of tumor size as a biomarker of clinical response, but macroscopic volume changes often have late onset and slow rate. Dual anatomical and functional imaging techniques, such as PET/CT and diffusion-weighted MRI, are superior to purely morphological imaging for detecting peritoneal disease, and could facilitate preoperative planning. Molecular imaging techniques provide quantitative parameters for early assessment of treatment response; however, standardization and validation are still warranted for their wider application in drug research and clinical practice.

Conventional CT and MR imaging of peritoneal carcinomatosis has a satisfactory performance in most ovarian cancer patients throughout the course of their disease. Nevertheless, as more aggressive surgical approaches and individualized systemic treatments are being pursued, integrated anatomical and functional imaging must overcome the deficiencies of conventional imaging to fully delineate the extent of disease and assess treatment effects at a cellular level. The improved accuracy of PET/CT and DW-MRI in preoperative staging of ovarian cancer justifies the use of these modalities in selected cases until prospective studies determine a cost-effective imaging strategy. The assessment of treatment response with molecular imaging is still at an early stage, where technical improvements in data acquisition and analysis need to be supported by pathophysiological evidence relevant to tumor behavior and targeted disease pathways.

A greater understanding of the complexity of ovarian cancer has started to stimulate combination treatment strategies, such as the synergistic effect of cytotoxic and antiangiogenic or vascular disrupting agents, and targeted blockade of signaling pathways at multiple levels; a multiparametric approach is required, where biomarkers from different modalities (PET/CT, DW-MRI and DCE-MRI) can be combined into a broader evaluation scheme that takes into account the functional (metabolic, cellular and perfusional) changes within the tumor in response to treatment. Until these biomarkers and approaches are validated as independent predictors of clinical response, their role will be principally confined to clinical trials and accelerating drug development.