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Small Lymph-Node Metastases Identified With Magnetic Resonance Imaging, Plus Magnetic Nanoparticles In Prostate Cancer

High-resolution magnetic resonance imaging (MRI) used in conjunction with magnetic nanoparticles enables the identification of small, and otherwise undetectable, lymph- node metastases in patients with prostate cancer.

"On a patient-by-patient basis, the addition of lymphotropic superparamagnetic nanoparticles increased the sensitivity of MRI from 45.4 to 100%, with a specificity of 95.7%," reports Ralph Weissleder, M.D., Ph.D., of Massachusetts General Hospital, Charlestown, United States, and colleagues. The research team prospectively analysed the accuracy of this detection method in 80 patients with biopsy-proven stage T1, T2, or T3 prostate cancer.

The patients underwent MRI both prior to and 24 hours following the intravenous administration of lymphotropic superparamagnetic nanoparticles (2.6 mg of iron per kilogram of body weight in saline solution administered over 15 to 30 minutes).

Sixty of the patients had open resections and 15 patients underwent laparoscopic resection. In 5 patients, computer- tomography-guided biopsy identified the presence or absence of nodal metastases in specific lymph nodes and no surgery was performed.

The researchers evaluated 334 lymph nodes with direct MRI and histologic correlations. Of these 271 (81.1%) were benign while 63 lymph nodes (18.9%), collected from 33 patients, contained microscopically detectable metastases.

Of the 63 malignant lymph nodes, 17 measured less than 5 mm, 28 measured 5 to 10 mm, and the remaining 18 were larger than 10 mm. The investigators note that 71.4% of the malignant nodes did not meet the traditional imaging criteria (greater than 10 mm if elongated or more than 8 mm if rounded) for malignancy.

Lymph-node metastases can be accurately diagnosed by high- resolution MRI with lymphotropic superparamagnetic nanoparticles, the researchers conclude, but not by conventional MRI. Such a sensitive and reliable method for detecting lymph-node metastases in men with prostate cancer is an important factor in the determination of local versus advanced disease and their respective therapies.
N Engl J Med 2003;348:2491-9.

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