Is there anything microwaves can't do?

They'll bring your day-old spaghetti back to life, heat up your queso in a matter of seconds. Also, they might help relieve pain and cure some cancers.

Which is a pretty neat trick as well. A new technology called microwave ablation is raising hopes that microwaves could soon be used not just to destroy existing tumors, but also to stop new ones from forming in the first place. Mmmm [♪ INTRO] Microwaves seem to belong squarely in the kitchen, but they’ve actually been used in medicine for a pretty long time.

And they seem a little bit magic, so here’s how they work: A microwave is a type of electromagnetic radiation, like visible light, or radio waves, or x-rays. It’s got a specific wavelength: from 1 millimeter to 1 meter. Microwaves carry more energy than, say, the 3 meter radio waves that carry tunes for FM radio, but less energy than nanometre-sized x-rays.

And if you can make these waves and then change their direction very quickly, then polar molecules, those with a negative end and a positive end, will try to keep up. Water is just such a molecule, and it gets really agitated in the presence of oscillating microwaves. But non-polar materials like ceramics, and plastics, and bones aren’t really bothered.

This can be annoying when you are trying to reheat something that doesn’t respond well to microwaves, but it will become important later; remember that it is only water and other polar molecules that react to these oscillating microwaves. In the 1920s, magnetrons were invented that could make powerful microwaves, and they were greatly improved in the ‘40s. And that was very useful for applications like radar, but also, it turns out, medicine.

Soon, doctors began investigating how microwaves could be used for healing. And from the very first studies, it was clear that by heating tissues, you could increase blood flow. That had all sorts of benefits, not least of which was pain relief.

One theory is that increased blood flow increases all the good stuff flowing to the area. Muscles and other tissues love oxygen, nutrients, and cells that specialize in repairing damage. The blood brings all those things right where they need to go.

And bonus, the increased blood flow also increases the rate at which bad stuff gets washed away. And so “microwave diathermy,” the fancy medical term for “heating somebody up with microwaves,” is sometimes used to treat muscle and bone issues like shoulder injuries, knee problems, and tendon issues. But it’s basically just a way to get heat to an area.

It’s the heat that does the healing. As the technology developed, doctors were able to better target the exact area they needed to. And by using cooling pads to keep the skin cool, they could keep the heat where it was needed without causing damage.

It wasn’t too long until another group of doctors started getting interested in microwaves: Oncologists Sports doctors usually try to keep temperatures in the low 40s Celsius, because any higher than that and proteins start denaturing and cells start to die. And that, you know, sounds bad. It’s usually bad… Unless cell death is what you’re after.

Because cells, of course, tend to be full of water, they are very susceptible to microwaves. But just placing somebody in a giant microwave oven would cook all of their cells, so oncologists have to be a lot more precise. Instead, they insert a tiny probe that creates microwave radiation around the end of the probe.

It heats up only the nearby cells and can be very accurately controlled. This method is called microwave ablation and it’s gaining traction in oncology as a reliable way to kill cancerous tumors, especially in the liver. Cutting out a tumor with surgery is probably the most straightforward treatment.

But it turns out that cutting out liver tumors is really hard. The majority of liver tumors are actually inoperable. That could be for a few different reasons.

It might be that the tumor is too close to major blood vessels, because it’s spread too much in the liver already, or because the person isn’t otherwise healthy enough to go through a surgery. The liver is also a common place for cancers to spread to, also known as metastasis, because so much of your blood passes through it on a daily basis. So here is how microwave ablation for a liver tumor usually works: First, doctors insert a small needle with a microwave antenna at the end into the liver and they guide it directly into the tumor.

Then they turn on the microwave generator, and the tip of the antenna causes a field that heats up nearby tissue. By precisely controlling how long the antenna is on and how much power is delivered, the doctors can precisely control how big the affected area gets. Typically, they will aim to destroy the entire tumor and 1cm around it in all directions, just to be safe.

Microwave ablation is effective, and more and more cancer centers are turning to this technology. An even newer advance is the combination of microwave ablation with magnetic nanoparticles. By injecting tiny pieces of material like metals or carbon nanotubes into the tumor first, it can make the microwaves even more effective.

Think of it kind of like strategically putting metal in the microwave to get those sparks exactly where you need them. Another booster for microwave ablation might be the immune system itself! In a study published in 2021, researchers found that the immune systems of patients who had MWA for their early-stage breast cancer actually showed the markers of being better-equipped to fight the cancer.

In another 2020 study in mice, researchers showed that mice with metastatic breast cancer had better survival rates after being treated with microwave ablation than with surgery. So here’s the theory: in MWA, the charred remains of the tumor are left behind and your immune system is able to learn what the tumor looked like. Compare that to surgery, which totally removes the enemy along with any evidence your immune system can use if the cancer comes back.

For some early-stage cancers, research is starting to show that microwave ablation is a viable option that may be better than surgery. Evidence is mounting that MWA is less invasive, causes less stress on the body, and it can help the immune system. While microwaves are certainly an exciting avenue of treatment, it’s important to remember that there is no silver bullet for cancer, because it is not just one disease.

But for people with certain cancers, this treatment may give an extra edge and save more lives. Not bad for a technology you probably most associate with a frozen burrito! Thanks for watching this episode of SciShow.

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