Although histotripsy, a novel technique utilizing high-frequency ultrasound waves to destroy tumors, is only being used in the liver, it is being looked at in other solid tumors, like kidney, prostate, and pancreas, explained Shaun P. McKenzie, MD, FACS, a surgical oncologist with Texas Oncology. He added that histotripsy starts in the liver, because the organ is very durable and that’s the area with the most experience with ablative therapy.
Transcript has been edited; captions are auto-generated.
Transcript
It seems liver cancer is the only area in which histotripsy is being used. Why is it so successful in liver cancer?
Liver cancer is a general term, right? The reality is, because liver is a filter organ, 50% of the tumors we see in the liver are actually metastases from other cancers, and those cancers are considered potential targets for treatment with histotripsy. Actually, you can treat a lot of different cancers. For example, I’ve treated 2 patients with breast cancer, I’ve treated a patient with metastatic pancreatic cancer, but then also bile duct cancer and hepatocellular carcinoma, which happened in the liver. Those are treatments.
The reason that we’ve really started in the liver is because that is where [we have the] most of the experience with what we refer to as ablative therapy. Ablative therapy means we’re not removing the tumor; we’re killing the tumor with either radiation or microwave energy or radiofrequency energy, or now, ultrasound energy. The concept was: let’s start somewhere where we know ablative therapy has worked before.
The other great thing about the liver is, because it’s a solid organ, it does tend to push other critical structures away. It’s a safe target. Then, the last thing, of course, is our liver is pretty durable. We already know we can do things like this to the liver, and it will be well tolerated.
Now, I will tell you that this technology is being looked at in kidney. It’s being considered potentially for prostate, and it is also being evaluated in pancreas. There is a hope that this technology will have broader applications over time, but right now, it’s so new that they really wanted to start in a place that they thought would be the safest place to start. That’s the main reason that liver tumors have been first on the list.
Do we have data on relapse rates or long-term outcomes of patients treated with histotripsy?
That’s the best question, because that’s the problem right now, right? The problem right now is there is a paucity of data. What has been published has been the safety data, which it has shown to be safe, and that’s how it got FDA approval. What there has been, although they haven’t really published it well, but we’ve certainly seen, is it does appear to destroy tumors. We know that, but what we don’t know—and this is always the concern about being on the front edge of some of these new technologies—is there has been no publication that has described recurrence rates over a 2- or a 5-year period, which, of course, are the gold standard times that we look at, and certainly overall survival numbers.
Does [histotripsy] really help people live longer? And the answer is, we don’t know yet. What we are extrapolating is that ablative therapy, when used for these cancers in the past, has a good track record. And because this technology does appear to be successful in ablating tumors, we should, at a minimum, see the same outcomes, right? But again, that’s a lot to assume. There is absolutely a plan—in fact, there’s a national study that they’re trying to open at every site where all of your patients will be tracked, their recurrences, their survival and all that, so that they can actually publish long-term outcome data. Because that’s really going to be key before you can really say anything in terms of how does histotripsy fit into the standard of care for liver tumors.
