Abstract CT222: Ferumoxytol enhanced MRI for lymph node staging in genitourinary cancers

Background: Conventional imaging has limited accuracy in genitourinary (GU) cancer staging. This study examines the utility of ferumoxytol enhanced MRI in lymph node (LN) staging of GU cancers. Methods: This ongoing IRB-approved phase II clinical trial enrolls patients with prostate cancer, renal cell carcinoma, or bladder cancer at high risk for LN metastases. Patients undergo baseline T2 and T2* weighted MRI scans followed by injection of 7.5mg/Kg ferumoxytol. Repeat scans are acquired at 24hr and 48hr post-injection. The criterion for positive LNs was preservation of hyper-intense signal indicating failure to take up ferumoxytol. Validation was by histopathology when available or on clinical grounds, for which LNs that changed size on routine imaging were considered true positives. Results: To date, 13 patients have completed the study. Of 11 prostate cancer patients, one was studied pre-operatively while 10 had suspected therapy failure. Median age and PSA were 65yrs (36-75) and 5.6ng/mL (0.3-201). The other 2 patients had renal cell carcinoma and bladder cancer. Overall, 20 LNs were identified with mean size 1.9cm (0.7-3.8) long axis by 1.3cm (0.6-2.6) short axis. There were 14 true positive LNs, 1 false positive, 1 false negative, and 4 nodes pending validation. Validation was by histopathology for 7 LNs, with 2 nodes pending biopsy, and clinical grounds for 13 LNs, with 2 inconclusive nodes awaiting further validation. Ferumoxytol correctly identified LN status in 9 of 10 patients with validated nodes (Table 1). Conclusions: Ferumoxytol enhanced MRI shows promise in detecting malignant LNs >6mm in GU cancer patients. Since the method involves a conventional MRI unit with off-label use of an FDA-approved agent, it could be widely available. However, further validation is necessary before routine use. Table 1: Preliminary results for LN staging in GU cancer patients using ferumoxytol enhanced MRI SubjectStudy ArmGenderAge (yr)PSA at study initiation (ng/mL)LN numberLN locationsize/long axis (cm)size/short axis (cm)Ferumoxytol positive? 1 = yes, 0 = noResult1prostate cancerM6325.061R ext iliac3.02.61TP2L ext iliac1.30.81TP2prostate cancerM6573.961L RP1.61.41TP2L int iliac3.81.91TP3prostate cancerM6410.491R ext iliac3.00.91pending2L ext iliac1.91.10pending4prostate cancerM742.061L RP1.71.51TP5prostate cancerM642.891R ext iliac1.61.11TP6prostate cancerM650.281L int iliac1.50.81TP7prostate cancerM752.871R int iliac0.70.71TP8prostate cancerM6427.911R commo