Osaka Liver Cancer Study Tests Ultrasound Bubbles as an Alternative to Surgery

Japan begins testing a treatment that breaks apart liver tumors

Osaka Metropolitan University has begun Japan's first specified clinical study of histotripsy for liver cancer, using focused ultrasound to create tiny bubbles that mechanically break apart tumors. Two patients had received treatment by October 2026. The study targets tumors measuring no more than 3 centimeters and will assess whether the treatment can destroy the selected tissue safely, with patients potentially leaving hospital the following day.

The government's clinical study registry gives the research a precise first test: a scan with contrast material on the day after treatment will check whether the targeted lesion has been liquefied. Researchers will also record adverse events and assess treatment costs and scheduling. The registered study is scheduled to end on June 30, 2028.

Professor Takeaki Ishizawa, a surgeon specializing in the liver, bile ducts and pancreas at Osaka Metropolitan University Hospital, leads the research. Eligible patients have either hepatocellular carcinoma, a cancer that begins in the liver, or cancer that has spread to the liver from another part of the body.

The attraction is practical. Surgery requires an incision, while commonly used ablation treatments insert a needle into the tumor. Histotripsy directs its treatment energy from outside the body. For selected patients, that could mean less physical strain and a shorter hospital stay.

Japan's study is at phase 1–2, an early stage focused on short term effectiveness, safety and whether the procedure can be delivered in practice. The device remains unapproved in Japan, and the university's ambition is to turn this research into another treatment option, including for older people who cannot undergo surgery.

How ultrasound bubbles destroy tissue

Histotripsy uses sound energy to break tissue apart rather than burning it. A dedicated system concentrates powerful ultrasound pulses on a small point inside the liver, creating microscopic bubbles in the targeted tissue.

The bubbles expand and collapse, producing mechanical forces that disrupt cells and turn the selected tissue into liquid. At Johns Hopkins Hospital in Baltimore, where the technique is already used, clinicians describe the resulting material as waste that the body subsequently clears.

The Japanese protocol specifies ultrasound pressures of 15 to 25 megapascals, with each pulse lasting less than 10 milliseconds. The energy is focused on a spot measuring 3 to 6 millimeters across. A millisecond is one thousandth of a second, so these are very brief bursts concentrated into a small area.

Radiofrequency ablation works differently. A doctor inserts a thin electrode into a tumor and uses heat to kill the tissue. Microwave ablation also uses heat delivered through a needle. Histotripsy instead relies on the physical action of bubbles generated by ultrasound coming from outside the body.

Who can enter the Osaka study?

Osaka's registered eligibility rules cover adults aged 20 or older and younger than 90 who have hepatocellular carcinoma or cancer that has spread to the liver. The lesion selected for treatment must measure no more than 3 centimeters at its widest point.

Doctors must also be able to see the entire target lesion with an abdominal ultrasound examination. That requirement matters because they need a clear image of the tissue they intend to treat, as well as a suitable route for the ultrasound energy to reach it.

Ishizawa developed the Japanese research plan after learning about histotripsy at a medical conference in the United States. His team has treated two patients and plans to assess additional cases as needed. The registry does not state a planned total enrollment, and individual results for the first two patients have not been disclosed.

What researchers will measure first

The study's main measure of effectiveness is the appearance of the treated lesion on a contrast enhanced CT scan the next day. Contrast material helps doctors distinguish structures and tissue on the images. Researchers will check whether the targeted lesion has been liquefied.

Safety checks will record adverse events, including complications identified after treatment. The university describes checking for bleeding and other problems before deciding whether a patient can leave hospital the following day.

The research also includes a practical assessment of treatment cost and scheduling. Hospitals need to understand how the procedure fits into care, alongside whether it achieves its immediate biological goal. The study therefore combines an imaging assessment with checks on patient safety and delivery.

Long term cancer control and survival after histotripsy remain uncertain. Those outcomes require follow up over a much longer period than a scan taken the next morning. At present, the Osaka protocol's primary focus is the immediate response of the treated tissue.

Why a shorter hospital stay matters

Patients undergoing established treatments such as surgery or radiofrequency ablation commonly spend several days to around 10 days in hospital, according to the university's description. Osaka's proposed next day discharge pathway could shorten that stay for patients whose recovery checks show no abnormality.

Japan's aging population makes the physical demands of cancer treatment a central concern. The university says some patients cannot receive sufficient treatment because doctors must account for the strain on their bodies. Ishizawa hopes histotripsy will widen the choices for people whose age or condition makes surgery difficult.

Ishizawa, who leads the Osaka team, described both older patients and younger people seeking an earlier return to their usual activities:

The new treatment could allow treatment for older people who cannot undergo surgery, and could also help younger patients return to social activities sooner. I want to open a path toward a cure for patients.

For patients and families, a shorter admission could reduce time away from work, caregiving and daily routines. The research must establish how often that recovery pathway is achievable and what complications occur.

What treatment looks like at Johns Hopkins

Johns Hopkins Hospital offers a concrete example of how histotripsy is delivered abroad. Patients undergo an outpatient procedure lasting a few hours, with much of that time spent adjusting the equipment and accurately locating the target. They can return home the same day.

The Baltimore team uses general anesthesia to keep patients still during treatment. An interventional radiologist, a doctor who performs procedures guided by medical images, uses ultrasound to locate and monitor the tumor. General anesthesia is part of that hospital's described practice; details of anesthesia in the Osaka study have not been specified.

At Johns Hopkins, the equipment is based in radiology under the supervision of Robert Liddell and Christos Georgiades. Radiology director Karen Horton supported its introduction. Several doctors in the interventional radiology service have completed training, building the treatment around a team already experienced in using live images to guide procedures.

The hospital has mainly treated liver tumors, although it also describes treating one patient with a kidney tumor. Its account states that United States regulatory authorization covers liver tumors, while use for kidney tumors is being studied in clinical trials.

Small tumors and a clear ultrasound view

Johns Hopkins currently describes its most suitable candidates as people with one or a few tumors smaller than 4 centimeters in parts of the liver that ultrasound can readily show. Osaka's study uses a tighter size limit of 3 centimeters, alongside its own age and imaging requirements.

Tumor position can be as important as size. Ultrasound travels poorly through air and bone. Ribs covering a tumor, or bowel lying across the route of the sound waves, can make treatment more difficult. Large tumors or numerous tumors are also less suitable under the approach described by the Baltimore team.

Patients therefore need an assessment of where their tumors sit and how well they can be seen. Two people with tumors of the same diameter may have different treatment options because the surrounding anatomy differs.

Encouraging early experience, with longer follow up needed

More than 2,000 patients have received histotripsy overseas, including in the United States, according to the account of Osaka's introduction of the procedure. The technique received United States authorization for liver tumor treatment in 2023.

Christos Georgiades, a professor of radiology and director of interventional oncology at Johns Hopkins, has described encouraging early responses, including complete regression of some tumors over a few months. He also set out the current limit of that experience:

I am very hopeful, but it is still early days. The early results are encouraging, but we do not yet have long term data.

Norihiro Kokudo, a liver surgeon and president of the Japan Institute for Health Security, pointed to the potential reduction in physical strain compared with ablation. His assessment focused on the absence of a treatment needle and heat:

Because it uses neither needles nor heat, it may place less strain on patients than ablation therapy. If this technique becomes available in clinical practice in Japan, it would be good news for many patients.

Osaka's research will add experience from patients treated in Japan to that overseas record. Its immediate contribution will be detailed checks of tissue destruction, adverse events and the practical demands of treatment in the participating hospital.

The timetable for research and access

The government registry identifies the study as specified clinical research and lists Gunze Medical as the provider of both the unapproved histotripsy system and research funding. It records recruitment as ongoing.

The milestones span several months in 2026, followed by a study completion date in 2028:

• March 4, 2026: A certified clinical research review committee approved the study.
• June 30, 2026: A university announcement of the study's start is cited in the clinical account describing the introduction of histotripsy in Japan.
• July 6, 2026: The registry records enrollment of the first participant.
• September 14, 2026: The registry gives this as its notification and latest publication date.
• By October 21, 2026: Two patients had received treatment, and the team was describing its plans for regulatory approval and public insurance coverage.
• June 30, 2028: The registered study period is scheduled to end.

The team aims to obtain Japanese regulatory approval during 2027 and secure public insurance coverage. Approval would address whether the device can be marketed for its intended use; insurance coverage would determine whether treatment is paid for through Japan's public health insurance system. Both remain goals while the study proceeds.

Key Points

• Osaka Metropolitan University has treated two patients in Japan's first specified clinical study of histotripsy for liver cancer.
• The study covers selected adults with liver tumors no larger than 3 centimeters that can be fully seen on ultrasound.
• Focused ultrasound creates bubbles that mechanically break apart tissue, without inserting a treatment needle into the tumor.
• The main effectiveness check is a CT scan the next day to assess whether the targeted lesion has liquefied.
• Patients may leave hospital the following day if checks show no complications.
• The device is unapproved in Japan. The team seeks approval in 2027, while the registered study ends in June 2028.
• Early overseas experience is encouraging, but long term cancer outcomes remain uncertain.