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Abstract #3419

R1 and R2* Mismatch on Ferumoxytol-Enhanced MRI Predicts Response of Breast Cancer Brain Metastases to Liposomal Irinotecan

Harshan Ravi1, Andres M. Arias Lorza1, James R. Costello2, Hyo Sook Han3, Daniel K. Jeong2, Stephan G. Klinz4, Jasgit C. Sachdev5, Ronald L. Korn6, and Natarajan Raghunand1,7
1Department of Cancer Physiology, Moffitti Cancer Center and Research Institute, Tampa,, FL, United States, 2Department of Radiology, Moffitti Cancer Center and Research Institute, Tampa, FL, United States, 3Department of Breast Oncology, Moffitti Cancer Center and Research Institute, Tampa, FL, United States, 4Ipsen Bioscience,, Cambridge,, MA, United States, 5Honor Health Research Institute, Scottsdale,, AZ, United States, 6Imaging Endpoints Core Lab, Scottsdale,, AZ, United States, 7Department of Oncologic Sciences, University of South Florida, Tampa, FL, United States


Phagocytosis of ferumoxytol (FMX) by tumor-associated macrophages (TAMs) results in intracellular compartmentation, which has opposing effects on longitudinal (R1) and transverse (R2*) relaxivity of FMX. Pixelwise mismatch between apparent ferumoxytol concentration (FMXc) computed from post-FMX R1 and R2* maps can be exploited to identify pixels with high concentrations of phagocytosed (compartmentalized) FMX. Here we show mismatch on MRI, acquired 24 h post-FMX, measured in terms of compartmentation index (CI) greater than 1 and hypothesized to be indicative of FMX intracellular compartmentation, was predictive of the response of breast cancer brain metastases to liposomal irinotecan (nal-IRI) at the individual tumor level.

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