High-resolution MRI with magnetic nanoparticles is highly sensitive in detecting clinically occult lymph-node metastases in prostate cancer, according to a new report. In fact, routine use of this modality preoperatively could obviate many unneeded surgeries.
The nanoparticles, which are given intravenously 24 hours before scanning, work by binding to lymphatic cells. The particles only bind to normal cells, so it is the areas that do not "light up" on MRI that are suspicious for malignancy.
MRI with magnetic nanoparticles "is very likely going to change the way cancers can be staged," say senior doctors. "In the study 25% of patients could have avoided surgery if scanning with nanoparticles had been done preoperatively." Currently, there is no way of knowing before surgery which patients will have microscopic tumor spread to the lymph nodes.
The findings, which are published in the June 19th issue of The New England Journal of Medicine, are based on a study of 80 men with prostate cancer who underwent lymph-node resection or biopsy. Prior to surgery, MRI was performed in all patients before and after infusion of nanoparticles. Of the 334 nodes removed, 63 had histologically proven metastases. With standard imaging criteria for malignancy, 45 of these nodes would have been falsely considered disease free.
MRI with nanoparticles correctly identified all of the patients with nodal disease. In addition, on node-by-node analysis, the sensitivity of this modality, at 90.5%, was significantly higher than that of conventional MRI, at 35.4% (p < 0.001). The nanoparticles appear to be very safe and none of the patients experienced any side effects so far.
The team has also tested the agent's ability to detect metastases from lung and breast cancer and it appears to work equally well. "That's the beauty of targeting normal cells rather than focusing on the malignant cells which always mutate ."
The nanoparticles, which are being developed by Massachusetts-based Advanced Magnetics Inc. under the name Combidex, are in the final stages of approval by the US Food and Drug Administration.