New Contrast Agent Reveals Otherwise Undetectable Lymph-Node Metastases

Laurie Barclay, MD

June 18, 2003

June 18, 2003 — A new magnetic resonance imaging (MRI) contrast agent made up of superparamagnetic nanoparticles that are tropic for lymph nodes can accurately detect clinically occult lymph-node metastases from prostate cancer, according to the results of a prospective study published in the June 19 issue of the New England Journal of Medicine.

"MRI provides images with excellent anatomical detail and soft-tissue contrast but is relatively insensitive for the detection of lymph-node metastases," write Mukesh G. Harisinghani, MD, from Massachusetts General Hospital in Boston, and colleagues. "We investigated whether highly lymphotropic superparamagnetic nanoparticles, which gain access to lymph nodes by means of interstitial-lymphatic fluid transport, could be used in conjunction with high resolution MRI to reveal small nodal metastases."

Before undergoing surgical lymph-node resection or biopsy, 80 patients with presurgical clinical stage T1, T2, or T3 prostate cancer had MRI before and 24 hours after intravenous administration of the new contrast agent.

Of 334 lymph nodes resected or biopsied, 63 (18.9%) from 33 patients (41%) were histologically positive for metastases. Of 45 positive nodes not revealed by noncontrast MRI (71.4%), all were detected by MRI using the new contrast agent. Node-by-node analysis revealed a significantly higher sensitivity compared with conventional MRI (90.5% vs. 35.4%; P < .001).

"Aspects of cost and outcome of MRI with lymphotropic superparamagnetic nanoparticles will have to be studied in larger, prospective clinical trials," the authors write.

In an accompanying editorial, Dow-Mu Koh, FRCR, and colleagues from the Royal Marsden Hospital in Sutton, U.K., review this study and other "new horizons" in oncologic imaging.

"Despite the encouraging findings, the success of MRI with lymphotropic superparamagnetic nanoparticles may still be limited by the size of the involved nodes," they write. "A cost-effectiveness analysis may be necessary to determine the appropriate clinical use of this technique."

N Engl J Med. 2003;348: 2487-2488, 2491-2499

Reviewed by Gary D. Vogin, MD

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