Siemens HX4: A New PET Marker of Tumor Hypoxia

On September 29^th, Siemens announced that the company had completed a phase II study of their new tumor hypoxia Positron Emission Tomography tracer HX4 (link).  The ability to identify hypoxic tumors through imaging is of great significance to the personalized management of a broad variety of cancers since hypoxic tumors tend to be more resistant to radiotherapy and chemotherapy.

HX4 is not the first PET tracer developed as a biomarker of tumor hypoxia.  For instance, F-MISO ([¹⁸F]‑Fluoromisonidazole) has been tested with some success in the clinic (reference) but its relatively slow rate of clearance from the body have limited the utility of this tracer (link).  In contrast, HX4 has demonstrated a faster clearance from the body while maintaining a reproducible uptake by hypoxic tumors, producing higher image contrast within a relatively short period post-injection (i.e. 145 minutes).

Of note, HX4 has not yet been approved but is intended for world-wide distribution by PETNET Solutions, a wholly owned Siemens subsidiary which already provides PET tracers such as [¹⁸F]FDG and Na[¹⁸F] for metabolic uptake and bone metastasis imaging, respectively.