FDA Approves PEG Hydrogel Embolic System for Hypervascular Tumors

The Embrace Hydrogel Embolic System (HES), a polyethylene glycol (PEG) hydrogel embolic system, has received US premarket approval for the embolization of hypervascular tumors in peripheral arteries, marking a significant advancement in interventional oncology.¹

This approval is particularly notable as it is the first and only liquid embolic approved for this indication based on a prospective, randomized, controlled clinical trial. The system is designed to provide a new therapeutic option for cancer patients with tumors characterized by an abnormal increase in blood vessels, which are often challenging to treat surgically due to the high risk of bleeding.

Mechanism of Action and Clinical Efficacy

The FDA approval was supported by a pivotal multicenter study (NCT04523350) that enrolled 150 patients with hypervascular tumors across 22 institutions.² The trial randomized patients to receive either the PEG hydrogel embolic system or the standard of care, such as transcatheter arterial embolization (TAE) or conventional transarterial chemoembolization (cTACE).

Results from the study demonstrated that the PEG hydrogel system met its primary safety and effectiveness end points. It achieved an 88.6% technical success rate, defined as the delivery of the embolic agent to the tumor-feeding vessel with stasis of flow. Furthermore, the system showed a 99% freedom from major adverse events at 30 days postprocedure as adjudicated by a clinical events committee.

“The pivotal trial was designed to evaluate the Embrace HES system in patients with hypervascular tumors,” said Nadine Abi-Jaoudeh, MD, chief of Interventional Radiology at the University of California, Irvine, and national principal investigator of the study, in a press release.¹ “Embrace HES is the first liquid embolic approved specifically for this indication, with a unique design that enables deep penetration into vessels as small as 10 microns.”

The unique mechanism of the PEG hydrogel embolic system is a key differentiator. It consists of 2 low-viscosity liquid precursors that, when simultaneously injected into the blood vessels, rapidly crosslink in situ to form a soft, water-based hydrogel. This allows the agent to penetrate deeply into the fine, intricate network of a tumor's vascular bed, effectively occluding blood flow. This deep penetration capability, along with the avoidance of imaging artifacts, addresses several limitations of traditional embolic agents, such as potential catheter entrapment and incomplete embolization. The system's use of PEG, a biocompatible polymer with a long history of safe use in implantable medical devices, enhances its safety profile.

Addressing a Critical Unmet Need

Hypervascular tumors, commonly found in the liver, kidney, and bone, often present a formidable challenge to clinicians. Their high vascularity can lead to significant hemorrhage during surgical resection, increasing morbidity and complicating patient management. For patients who are not surgical candidates, TAE has become a cornerstone of treatment. However, achieving complete and persistent occlusion of the tumor vasculature remains a primary goal to prevent recanalization and disease progression.

The randomized design of the pivotal study provides a high level of evidence supporting the use of the PEG hydrogel embolic system in this clinical setting. The system's performance, including its ability to provide a cohesive, conformable embolization without requiring solvent-based agents or particle sizing, positions it as a promising new tool for interventional radiologists.

REFERENCES:

1. Instylla Gains U.S. FDA Premarket Approval for Embrace™ Hydrogel Embolic System. News release. Instylla Inc. August 7, 2025. Accessed August 7, 2025. https://tinyurl.com/yc37dssu

2. Instylla HES Hypervascular Tumor Pivotal Study. ClinicalTrials.gov. Updated December 16, 2024. Accessed August 7, 2025. https://www.clinicaltrials.gov/study/NCT04523350