Efficacy of ferumoxytol as a lymphatic contrast agent in prostate cancer.

Abstract

186 Background: Ferumoxytol (Feraheme) is a ferromagnetic nanoparticle with lymphotrophic biokinetics, delivered to lymph nodes by normal macrophages. MRI suppresses normal lymph nodes containing Feraheme. Objective is to validate safety and efficacy in finding lymph node positivity in prostate cancer (PCa). Methods: Nonrandomized prospective evaluation of 178 consecutive PCa patients (pts) at high risk for lymph node spread enrolled 2/13-3/15. All received IV Feraheme. 177 received 6/mg/kg over 20 min. One pt received 3 mg/kg infusion. T2 MEDIC and T2* sequence imaging of abdomen and pelvis, given 24 hours later. Images reviewed by 2 board certified radiologists with same interpretations, blinded to clinical and histo-path info (pre-MRI TNM stage/PSA/Gleason). Nodes were deemed abnormal if they did not suppress after Feraheme infusion (group 1, 94 patients). Nodes were deemed suspicious if suppressed and met usual size criteria with high signal intensity on DWI and decreased ADC map values and morphologic features (group 2, 84 pts). 83 group 1 pts had CT biopsies (77 pelvis, 6 retroperitoneum);11 pts had open PLND. 382 lymph nodes sampled. 76 group 2 patients had CT biopsies (73 pelvis, 3 retroperitoneum); 9 pts had open PLND. 340 lymph nodes sampled. Rad-path correlation was performed. Nodes were stained; reviewed by a single pathologist with no knowledge of MRI findings. Histo-path results for each node were cataloged for later MRI comparison. Results: 90 group 1 pts (96%) proved metastatic PCa; 4 pts (4%) were normal. 68 group 1 pts (77%) had malignant lymph nodes not meeting usual imaging criteria. 39 group 2 pts (47%) showed metastatic PCa; 46 pts (53%) were normal. One group 2 pt had an allergic reaction with hives; infusion ceased at 3mg/kg; pt treated to full resolution with 50 mg IV Benadryl. Conclusions: Feraheme can evaluate lymphatic dissemination of metastatic disease in PCa patients, with a lower limit of resolution of focal lymph node metastases of 2-3 mm. Better resolution gives implications for therapeutic radiation planning of newly diagnosed or recurrent/metastatic PCa. Toxicity was very acceptable at 6mg/kg. Feraheme may play a significant role as a lymphatic contrast agent in the early dissemination of lymphatic metastatic disease.