Page 154 - 89Zr-Immuno-PET:Towards a Clinical Tool to Guide Antibody-based Therapy in Cancer

Chapter 7
image data and was found to be more than 25% ID at D6. By using the blood samples this activity was found to be present in the plasma fraction. Therefore, the presence of a significant CD20 antigen sink hampering tracer availability for tumor targeting can be ruled out in this study.
So far, two other clinical studies have been published on the use of 89Zr- labeled anti-CD20 with focus on prediction of toxicity for radio-immunotherapy treatment planning in patients with B cell lymphoma (13, 14).
The current study provides evidence for the use of 89Zr-rituximab-PET as an imaging biomarker to assess CD20 targeting. These results allow for further studies to assess whether 89Zr-rituximab-PET is able to predict which patients will or will not respond to repeated rituximab treatment, and select which patients will benefit from a change of treatment (dose optimization, switch to a different targeted therapy or ADC). Novel treatment options emerge, including new anti- CD20 mAbs as obinutuzumab and ofatumumab with enhanced capacity for cytotoxicity as well as mAbs for other targets, for instance the anti-CD38 mAb daratumumab, and antibody-drug conjugates (ADC’s) as brentuximab vedotin, an anti-CD30 mAb linked to the antimitotic agent monomethyl auristatin E (MMAE). Molecular imaging with immuno-PET is a promising strategy to guide individualized treatment to improve efficacy, reduce toxicity and costs of mAb treatment.
CONCLUSION
This study provides evidence for the use of 89Zr-rituximab-PET as an imaging biomarker to assess CD20 targeting, given the observed correlation between tumor uptake of 89Zr-rituximab and CD20 expression in biopsies. Therefore, 89Zr- rituximab-PET allows for further studies relating tumor targeting to clinical benefit of rituximab treatment in individual patients.
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