Ultrasound Shattered Rat Liver Tumors; Other Untreated Tumors Vanished
In rat liver tumor experiments, 9 of 11 animals with partially ultrasound-destroyed tumors not only showed no metastasis—untreated residual lesions vanished entirely; the mechanism was released antigens activating systemic immune response.
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One Cardiologist's Challenge Forced an Impossible Invention
When Zhen Xu first joined the University of Michigan lab, pediatric cardiologist Ahmad Rudomirsky gave a seminar describing how a patient died on the operating table during congenital heart surgery. He challenged the lab: could you invent a technique that performs true surgery without incisions—he emphasized true surgery because microwave, radiofrequency, and ultrasound heating ablation only cook tissue; they cannot truly remove it, useless to him. This seminar became the origin of what would later be called histotripsy; Zhen Xu decided on the spot to make it her doctoral dissertation, though she had no idea how.
— Zhen XuCavitation Was Dismissed as Uncontrollable for 50 Years
Cavitation—ultrasound causing bubbles in tissue to expand and contract, mechanically tearing cells—had been observed for nearly 50 years, yet the field believed it could only be controlled by injecting bubbles, otherwise it was random and harmful, like when air in lungs ruptures during imaging. Histotripsy's breakthrough was injecting nothing at all, using only natural nanoscale gas particles in body tissue: these bubbles have surface tension reaching 200 to 300 atmospheres, extremely resistant to cavitation. Precisely because lungs are themselves massive air bubbles, histotripsy still cannot treat lung cancer.
— Zhen XuSilencing the Device Paradoxically Unlocked Tissue Liquefaction
Zhen Xu, with no ultrasound therapy background, followed advisor Charles King's advice to "explore, don't read papers." She found a slaughterhouse in the phone book and went weekly to scavenge discarded pig hearts for experiments, trying every parameter but failing repeatedly, until a colleague complained the equipment was too loud. She did the opposite: raised the pulse repetition frequency above 20 kHz, beyond human hearing—the tradeoff was individual pulse energy actually went down. It was this quieter configuration, chosen for silence not strength, that made pig heart tissue produce a smoke-like phenomenon, creating a hole in one minute—the discovery moment of histotripsy in 2002.
— Zhen XuA Decade Nobody Funded; Only NIH Sustained the Work
After discovering the phenomenon in 2002, Zhen Xu spent nearly a decade—using high-speed cameras to capture microsecond, micrometer-scale bubble activity—before understanding the mechanism. She was blunt: no rational person would fund this kind of work, neither companies nor venture capital would pay for such fundamental research with no visible applications, only NIH funding sustained it. From the initial 2002 discovery to FDA approval for liver cancer treatment in 2023, the journey took 21 years.
— Zhen XuA Student's Personal Tragedy Redirected the Research
The turn to liver cancer came from a request by doctoral student Eli Vlaisavljevich—his mother died of liver cancer when he was young. At the time, the entire field worried that mechanically destroying tumor cells would promote metastasis, so the team designed a rat experiment: intentionally treating only 50–75% of liver tumors, simulating worst-case scenarios, then monitoring metastasis long-term. Control group rats all died within two or three weeks from aggressive hepatocellular carcinoma, but of 11 treated rats, 9 not only saw no tumor spread—even untreated residual tumors vanished completely, nowhere to be found.
— Zhen XuMechanically Destroying Tumors Unexpectedly Activated Systemic Immunity
The unexpected finding prompted the team to collaborate with tumor immunologist Cliff Cho to investigate, revealing the mechanism: cancer hides itself by suppressing local immune response, while histotripsy converts tumor cells into liquid debris and ruptures cell membranes, releasing previously sequestered tumor antigens into circulation. The body then searches and attacks matching antigens not just at the treatment site but throughout the body—essentially replicating immunotherapy without injecting any drug—also explaining why treating one tumor shrank untreated lesions elsewhere. Zhen Xu emphasized this effect varies by individual, and the team is still exploring how to optimize parameters to amplify it.
— Zhen XuHOPE4LIVER Trial: 90% of Treated Tumors Stayed Gone at One Year
The multicenter clinical trial HOPE4LIVER was the direct basis for FDA approval of histotripsy for liver cancer treatment. Data showed low adverse-event rates; at 30-day follow-up, imaging-confirmed ablation success rate was 96%; at one-year follow-up, local tumor control rate was 90%. Because it's minimally invasive, doctors cannot directly confirm it visually like open surgery, so the entire procedure relies on imaging guidance—doctors outline the tumor on the image, software plans the robotic arm's scanning path accordingly, the doctor confirms and clicks start, and the robot completes treatment automatically, while bubbles from tissue destruction themselves serve as natural ultrasound contrast, letting doctors watch treatment in real time.
— Zhen Xu$40 Million Federal Funding Became a $3.75 Billion Company
When accepting the Golden Goose Award, Zhen Xu released a set of figures: over roughly 20 years, NIH invested about $40 million funding histotripsy research—early on, no company or investor would fund such fundamental research with no visible applications. Today FDA has approved it for liver cancer treatment, over 5,000 patients have received treatment, HistoSonics is valued at $3.75 billion with 500 employees, and was named by Time magazine as one of the ten most impactful healthcare companies. Her conclusion: federal research funding is the fundamental driver of America's technological innovation leadership.
— Zhen XuIn their own words · checked verbatim
And in front of me, I saw there was like almost like a smoke coming out of the pig heart tissue. But it can't be because it's in a washer tank. And within a minute, I saw a hole through that pig heart tissue. And I thought I was dreaming.
Zhen Xu0:00
And Charles literally said, you know, just go ahead and explore. And don't read any papers.
Zhen Xu9:32
So either within the focus, exceeding that threshold, you have temptation, you have damage. And outside, you have no damage.
Zhen Xu27:12
The 11 mass treated, Nine of them, not only the tumor didn't spread, the remaining tumor was just gone. We're like looking for it everywhere. We couldn't find them.
Zhen Xu41:01
So this crazy patient went out and run 20 miles within the first week of her tumor treatment.
Zhen Xu53:40
And in my case, more than 90% of my research has been funded by National Institute of Health, NIH.
Zhen Xu1:02:02
Figures
| Time from discovery to FDA approval | 21 years (discovered 2002, FDA approval 2023) | 31:32 |
| Rat liver tumor complete regression rate | 9 of 11 | 41:01 |
| HOPE4LIVER trial 30-day imaging-confirmed success rate | 96% | 49:31 |
| HOPE4LIVER trial one-year local tumor control rate | 90% | 49:31 |
| Total patients treated with histotripsy | Over 5,000 | 56:52 |
| Clinical centers offering the treatment | 200 | 57:56 |
| Total NIH funding over ~20 years | ~$40 million | 1:03:08 |
| HistoSonics valuation | $3.75 billion | 1:03:08 |
| HistoSonics employees | 500 | 1:03:08 |
Glossary
- histotripsy
- A technique using focused ultrasound to create cavitation bubbles within tissue, mechanically pulverizing lesions without incisions.
- cavitation
- The violent expansion and collapse of nanoscale gas bubbles in tissue caused by ultrasound, mechanically disrupting cell membranes.
- HIFU (High-Intensity Focused Ultrasound)
- A therapy using high-intensity focused ultrasound to heat and thermally destroy tissue.
- diffraction limit
- The smallest physical size to which a focused ultrasound beam can be narrowed; histotripsy overcame this via threshold effects.
- Golden Goose Award
- Award recognizing initially unconventional federal research funding that ultimately produces major social impact.
How to listen
Medical device and deep tech founders, investors focused on research-to-market translation, and engineers interested in biomedical engineering.
The 32:42 segment uses anesthesia, radiotherapy, and endoscopy history as analogies; information density is low; skippable.