Scientists used focused ultrasound and had managed to disrupt almost 75% of the volume of a tumor in the liver. The treatment also triggered the rats’ immunity to take over and clear the rest.
The cancerous tissues had been destroyed in almost 80% of the rodents and had shown no signs of metastases or recurrence in the 3 months that they were monitored, as per the scientists.
The treatment is known as histotripsy and is currently being trialed in humans who are afflicted with liver cancer.
“Histotripsy is a promising option that can overcome the limitations of currently available ablation modalities and provide safe and effective non-invasive liver tumor ablation,” said biomedical engineer Tejaswi Worlikar of the University of Michigan.
“We hope that our learnings from this study will motivate future preclinical and clinical histotripsy investigations toward the ultimate goal of clinical adoption of histotripsy treatment for liver cancer patients.”
HISTOTRIPSY: THE TREATMENT DONE ON THE LAB RATS
This treatment was pioneered and developed at the University of Michigan and offers new hope for the patients who suffer from this deadly cancer. The 5-year survival rate for liver cancer is presently much lower than 18% in the United States.
Histotripsy uses an ultrasound transducer to disrupt cancerous tumors instead of bouncing off internal structures for imaging.
It works by ultrasound cavitation and is almost similar to the technique used to non-invasively break down fat cells to treat weight loss. Ultrasound waves are focused on the treatment area and the vibrations generate tiny bubbles in the targeted tissues. When these bubbles burst, the tissues get disrupted and it destroys that part of the tumor.
It is obviously not possible to target the entire tumor and the way these cancerous masses are positioned influences whether this technique is safe to use on the entire tumor.
Partial treatment had resulted in complete regression in almost 81% of the treated rats, as per the researchers. 100% of the control rats had shown tumor progression, by contrast.
“Our transducer, designed and built at [University of Michigan], delivers high amplitude microsecond-length ultrasound pulses – acoustic cavitation – to focus on the tumor specifically to break it up,” said biomedical engineer Zhen Xu of the University of Michigan.
“Even if we don’t target the entire tumor, we can still cause the tumor to regress and also reduce the risk of future metastasis.”
THE EXPERIMENTAL PROCEDURE AND RESULTS
22 laboratory rats were implanted with liver cancer, where half was left as a control group and the remaining were treated using histotripsy. They targeted somewhere between 50 and 75% of the tumor volume.
3 rats were treated to a lesser extent, where this technique targeted just 25% of the tumor volume.
After the treatment, the experimental rodents were euthanized and dissected to find out how successful the treatment had been. The scientists looked for signs of progression, metastasis, and immune markers.
The results that came from the control rats were poor as all of them showed signs of progression and metastasis. The tumors had reached their maximum size after 3 weeks allowed by ethical procedures and the animals were euthanized.
The treated rats fared much better. The treatment proceeded without any complications or side effects and 9 out of 11 rats showed tumor regression and experienced tumor-free survival for the rest of the study, for around 10 weeks.