Scientists eradicate liver cancer in rats with sound waves

(ORDO NEWS) — Rats afflicted with liver cancer have demonstrated the effectiveness of an amazing non-invasive treatment.

With the help of focused ultrasound, scientists managed to destroy up to 75 percent of the volume of a liver tumor. Also, the treatment seems to kick-start the rats’ immune system, which takes over and clears out the rest of the tumor.

According to the researchers, in 80 percent of the animals the cancer was eradicated and there were no signs of metastasis or recurrence during the three months of observation.

This treatment, called histotripsy, is currently being tested in people with liver cancer.

“Histotripsy is a promising technique that can overcome the limitations of currently available ablation techniques and provide safe and effective non-invasive ablation of liver tumors,” said biomedical engineer Tejaswi Vorlikar of the University of Michigan.

“We hope that the results of this study will stimulate future preclinical and clinical studies of histotripsy with the ultimate goal of clinically introducing histotripsy for the treatment of patients with liver cancer.”

Developed and pioneered at the University of Michigan, histotripsy appears to offer new hope for patients with one of the deadliest forms of cancer: the five-year survival rate for liver cancer in the US is now less than 18 percent.

This method uses an ultrasound transducer, not to reflect internal structures for imaging, but to physically destroy cancerous tumors.

The method works by ultrasonic cavitation – similar to the method used to non-invasively destroy fat cells in weight loss treatments. Ultrasound waves are sent to the treated area; vibrations create tiny bubbles in the target tissue. When the blisters collapse or burst, the tissue is destroyed, destroying that part of the tumor.

Often it is not possible to influence the entire tumor. The way the masses are located, their size, and stage can affect whether it is safe to use histotripsy on the entire tumor.

But even partial treatment led to complete regression in 81 percent of the treated rats, the researchers found. In contrast, 100 percent of the control rats showed tumor progression.

“Our transducer, designed and built at the [University of Michigan], delivers high-amplitude, microsecond-long ultrasonic pulses – acoustic cavitation – to focus on the tumor and destroy it,” said biomedical engineer Zhen Xu of the University of Michigan.

“Even if we can’t target the entire tumor, we can still cause the tumor to regress and also reduce the risk of future metastasis.”

As part of this study, 22 laboratory rats were implanted with liver cancer. Half were left as a control group, and the remaining 11 rats were treated with histotripsy, affecting 50-75 percent of the tumor volume.

Three more rats received less treatment: the histotripsy affected only 25 percent of the tumor volume.

After treatment, the rats were euthanized and dissected to determine how successful the treatment was. The researchers looked for signs of progression, metastases, and immune markers.

The prognosis for control rats was terrible. All 11 showed signs of progression and metastasis. Within three weeks, the tumors reached the maximum size allowed by ethical protocols, and the animals were euthanized.

But the treated rats fared much, much better. Not only did the treatment go without complications or side effects, the majority of the rats – nine out of 11 – experienced tumor regression and survived tumor-free until the end of the study, about 10 weeks.

Previous studies on histotripsy have shown that the treatment is effective in shrinking the tumor. The new work shows that it also significantly increases survival after treatment.

“This study demonstrated the potential of histotripsy for successful non-invasive tumor ablation and prevention of local tumor development and metastasis.

Even with partial ablation, complete local tumor regression was observed in 9 of 11 treated rats with no recurrence or metastasis up to the 12-week study endpoint, about as evidenced by the MRI and histology data,” the researchers write in their article.

“These results suggest that histotripsy does not increase the risk of metastases after ablation compared to controls. Future studies will continue to explore the safety, efficacy and biological effects of histotripsy for possible clinical applications.”


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