[89Zr]Zr-cetuximab PET/CT as biomarker for cetuximab monotherapy in patients with RAS wild-type advanced colorectal cancer

E. J. van Helden, S. G. Elias, S. L. Gerritse, S. C. van Es, E. Boon, M. C. Huisman, N. C. T. van Grieken, H. Dekker, G. A. M. S. van Dongen, D. J. Vugts, R. Boellaard, C. M. L. van Herpen, E. G. E. de Vries, W. J. G. Oyen, A. H. Brouwers, H. M. W. Verheul, O. S. Hoekstra, C. W. Menke-van der Houven van Oordt

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Abstract

Purpose: One-third of patients with RAS wild-type mCRC do not benefit from anti-EGFR monoclonal antibodies. This might be a result of variable pharmacokinetics and insufficient tumor targeting. We evaluated cetuximab tumor accumulation on [89Zr]Zr-cetuximab PET/CT as a potential predictive biomarker and determinant for an escalating dosing strategy. Patients and methods: PET/CT imaging of [89Zr]Zr-cetuximab (37 MBq/10 mg) after a therapeutic pre-dose (500 mg/m2 ≤ 2 h) cetuximab was performed at the start of treatment. Patients without visual tumor uptake underwent dose escalation and a subsequent [89Zr]Zr-cetuximab PET/CT. Treatment benefit was defined as stable disease or response on CT scan evaluation after 8 weeks. Results: Visual tumor uptake on [89Zr]Zr-cetuximab PET/CT was observed in 66% of 35 patients. There was no relationship between PET positivity and treatment benefit (52% versus 80% for PET-negative, P = 0.16), progression-free survival (3.6 versus 5.7 months, P = 0.15), or overall survival (7.1 versus 9.4 months, P = 0.29). However, in 67% of PET-negative patients, cetuximab dose escalation (750–1250 mg/m2) was applied, potentially influencing outcome in this group. None of the second [89Zr]Zr-cetuximab PET/CT was positive. Eighty percent of patients without visual tumor uptake had treatment benefit, making [89Zr]Zr-cetuximab PET/CT unsuitable as a predictive biomarker. Tumor SUVpeak did not correlate to changes in tumor size on CT (P = 0.23), treatment benefit, nor progression-free survival. Cetuximab pharmacokinetics were not related to treatment benefit. BRAF mutations, right-sidedness, and low sEGFR were correlated with intrinsic resistance to cetuximab. Conclusion: Tumor uptake on [89Zr]Zr-cetuximab PET/CT failed to predict treatment benefit in patients with RAS wild-type mCRC receiving cetuximab monotherapy. BRAF mutations, right-sidedness, and low sEGFR correlated with intrinsic resistance to cetuximab.
Original languageEnglish
JournalEuropean Journal of Nuclear Medicine and Molecular Imaging
DOIs
Publication statusE-pub ahead of print - 2019

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