Interventional oncology, or IO, uses imaging to guide minimally invasive, targeted therapies, reaching tumors through catheters and needles rather than large incisions. These innovative treatments can also be paired with traditional systemic treatments, such as immunotherapy and chemotherapy, or radiation. For some patients, IO can offer hope where traditional methods have run out of road.
Jack W. Jennings, MD, PhD, who has helped shape the field’s growth for more than a decade, remembers when a thriving IO landscape still felt like an aspiration. “I believed this should be the fourth pillar of oncological treatment, and it became a real mission for me that interventional radiology should be at the table,” said Jennings, senior vice chair and division director of interventional radiology for WashU Medicine Mallinckrodt Institute of Radiology (MIR). What began as a seat at the table at tumor boards has grown into a full-fledged subspecialty with a dedicated professional society and a host of clinical trials.
“It became a real mission for me that interventional radiology should be at the table.”
Today, Jennings believes the field has arrived. “Over the last five years, MIR has gone from doing a handful of clinical trials to running dozens of therapeutic studies, including impactful work in interventional oncology,” said Greg Williams, associate director of clinical research.
Whether treating the liver, stabilizing bone, freezing a breast lesion or targeting a brain tumor, the principle is the same: using imaging to deliver less invasive care that complements — not competes with — the previously existing foundation of cancer care.
Liver Cancer
Key trials: ROWAN; EMERALD-Y90
Condition: Hepatocellular carcinoma
Approach: Y-90 radioembolization + immunotherapy
Principal investigator: Christopher D. Malone, MD
Y-90 radioembolization uses a small catheter that delivers radioactive microspheres to the blood vessels that supply a liver tumor. Named for the isotope found in the microspheres, this radiation therapy is one of the fastest-growing liver-directed therapies in the country.
Two open-label, single-arm prospective trials — ROWAN and EMERALD-Y90 — paired radioembolization with immunotherapy, a combination approach aimed at improving treatment response in patients with unresectable hepatocellular carcinoma. “The concept at the heart of these two trials is essentially that radiation can help convert a ‘cold’ tumor into a ‘hot’ one, potentially making immunotherapy more effective,” said Williams.
ROWAN enrolled participants globally, while EMERALD-Y90 enrolled from approximately 20 locations around the U.S. WashU Medicine was a leading enroller for both trials.
The combination approach requires close collaboration from medical oncology, which principal investigator Christopher D. Malone, MD, said reflects one of WashU Medicine’s strengths. “What I think is unique about WashU is we’re very collaborative and very multidisciplinary,” said Malone, emphasizing the comfort he feels co-managing patients with hepatology, oncology and surgical colleagues. “In other healthcare settings, some clinical decisions are being made in silos rather than the specialties working in stride.”
Bone Cancer
Key trials: TRIBUTE; BOREALIS
Condition: Metastatic bone cancer
Approach: percutaneous ablation + radiation, cryoablation
Principal investigators: Jack W. Jennings, MD, PhD, and Resten Imaoka, MD
Radiation therapy has long been a cornerstone of palliative treatment for painful bone metasases, and MIR investigators are incorporating interventional methods for synergistic benefits. The small incisions used by interventional radiologists reduce wound-healing concerns, which means patients don’t have to stop chemotherapy. In cases of weakened bone, IO approaches can also stabilize as they treat, combining tumor ablation with vertebroplasty or cementoplasty to reduce pain and reinforce structure.
The Society of Interventional Radiology’s TRIBUTE trial combines ablation with radiation therapy for high-risk lesions. Notably, the study is using pain metrics as a key outcome, a divergence from the typical measure of tumor response. In 2025, WashU Medicine became the first site activated for the observational trial.
This trial highlights another defining feature of interventional oncology at MIR: collaboration with the other pillars of cancer care. Jennings and longtime collaborator Clifford Robinson, MD, professor of radiation oncology, serve as two of the four national leaders of the trial.
“This study is not only exciting because of what we’re investigating,” Jennings said. “It also sends the message that radiation oncologists and interventional oncologists are teaming up and that this model has industry support.”
“Getting straight to a tumor through the blood vessels could open a new door…”
For years, Jennings and Robinson have set a tone for interdisciplinary cancer care among colleagues and mentees. “It’s these relationships that break down barriers,” said Jennings. When radiation can no longer be delivered optimally or a cancer is particularly ornery, IO methods can offer options that are desperately needed. “But it takes a person of real integrity like Cliff to set egos aside and dialogue about what may be best for the patient.”
BOREALIS, another clinical trial currently enrolling patients, focuses on non-painful bone metastases, with a preventive aim: treat lesions earlier with cryoablation to reduce catastrophic downstream events. Ideally, this prevents the progression of bone metastases and events such as fractures or spinal cord compression.
Breast Cancer
Key trial: COOL-IT, COOL-IT Pro
Condition: Low-risk, early-stage breast cancer
Approach: cryoablation
Principal investigator: Heather V. Garrett, MD
Improvements in breast cancer screening mean cancers can be found earlier when tumors are smaller and more treatable. Lumpectomy remains the gold standard for early-stage breast cancer, but researchers have been studying ultrasound-guided percutaneous breast cryoablation as a less invasive alternative for selected patients.
Heather V. Garrett, MD, is leading two studies evaluating breast cryoablation — a clinical trial comparing it with lumpectomy and a prospective registry tracking long-term outcomes.
Smaller single-arm studies have shown promising results, but more data is needed. Breast cryoablation had been lacking a large, randomized clinical study, previously having only a host of smaller studies. Heather V. Garrett, MD, stepped in to fill the void with COOL-IT, a randomized controlled trial born out of Garrett’s collaboration with former IR resident Anurag Chahal, MD. The pair also received the support of Julie Margenthaler, MD, professor of surgery, who saw the need for a noninferiority trial and recognized Garrett’s expertise in the procedure.
“For some patients, it’s clear breast cryoablation has an advantage: no anesthesia, little or no recovery time, no breaks in chemotherapy or delays in radiation therapy,” said Garrett. “We hope this research will determine how cryoablation can best be integrated into standard breast cancer treatment and provide a less invasive option for our patients.” The complementary COOL-IT PRO is a registry study for breast cancer patients who undergo cryoablation because they are not surgical candidates.
Scaling the Fourth Pillar
Scaling IO as a mainstay of cancer care requires supportive systems. The 2025 opening of the Plaza West Tower boasts two complete floors of IR,multiple procedural CTs and hybrid imaging capability — physical infrastructure that can change the clinical reality for patients. “This IR facility is on a scale I’ve never seen comparable in the U.S.,” Jennings said.
MIR also received accreditation from the International Accreditation System for Interventional Oncology Services. It’s systematic quality and safety standards were developed through CIRSE, the largest interventional society in the world, and WashU was the first U.S. site to receive this accreditation. Jennings credited internal partners who helped evaluate and implement the accreditation, an effort he believes has strengthened patient experience and credibility while unifying a global IO community with a consistent set of standards.
Although Jennings believes the field has achieved its “fourth pillar” status in major medical centers, he sees patient and provider awareness as a gap to fill. “Patients may not realize that these minimally invasive procedures are being developed developed — that a big surgery isn’t their only option.”
As radiology trainees become skilled in IO approaches, medical teams around the country are able to expand their offerings to patients with cancer. As an example, Jennings points to three MIR alumni — two interventional radiologists and one musculoskeletal radiologists who practice in St. Joseph, Missouri. “Their radiation oncology and medical oncology colleagues have told me how grateful they are to those former MIR fellows for bringing interventional oncology there,” Jennings said. “And that gets me really excited.”
Published in Focal Spot Spring/Summer 2026 Issue