Hyperthermia: Why Heat Can Make Cancer Treatments More Potent

Heat can be an incredibly simple, yet powerful, way to boost the effects of chemotherapy and radiation treatments for cancer.

More than 5,000 years ago, doctors in ancient Egypt used heat to treat cancer. Today, cancer experts have refined the delivery of heat — a technique called hyperthermia — to improve radiation and/or chemotherapy outcomes for:

• Breast cancer.
• Brain cancer.
• Sarcoma (connective tissue cancer).
• Prostate cancer.
• Bladder cancer.
• Cervical cancer.
• Recurrent rectal cancer.
• Bone metastases.

“Hyperthermia typically improves the effectiveness of radiation therapy by about 50 percent, compared with using radiation alone,” says radiation oncologist Jennifer Yu, MD, PhD.

“Rather than killing cancer cells outright, mild temperature hyperthermia ‘primes’ cancer cells to be more susceptible to radiation or chemotherapy. It can also target tumor cells that prove resistant to radiation and chemotherapy.”

How heat affects cancer

Hyperthermia is different from “ablative” techniques, which use heat — from ultrasound waves, radio waves or lasers — to destroy cancer cells.

“In those treatments, the heat itself is high enough to ‘cook’ the cancer,” explains Dr. Yu. “In mild temperature hyperthermia, we use lower temperatures (109˚ to 110˚ F) to allow radiation therapy or chemotherapy to work better. This often shrinks the tumor.”

Hyperthermia makes a few different things happen during cancer treatment:

• It sensitizes cancer stem cells to radiation.
• It interferes with tumor cells’ ability to repair damage from radiation.
• It heightens the effectiveness of chemotherapy drugs.
• It increases blood flow to the tumor, making tumor cells more sensitive to radiation and improving delivery of chemotherapy to the tumor.
• It enhances the body’s immune response to the cancer cells.

How hyperthermia works

Cancer experts use different methods to heat tumors before or after radiation therapy.

They may use small microwave units to heat tumors located near the body’s surface. They may place probes within a body cavity, such as the rectum, to heat a tumor. Or they may surgically place a probe to heat a tumor deep within the body — for example, in the brain.

Cancer specialists typically do hyperthermia treatments twice a week over the course of radiation therapy. Each treatment takes about one hour.

Heat can also be delivered in different ways with chemotherapy.

Doctors may heat the blood that supplies a tumor, then deliver chemotherapy through the heated blood.

Or surgeons may heat chemotherapy drugs and circulate them through the abdomen and pelvis to treat tumors located there. The technique — called hyperthermic intraperitoneal chemotherapy (HIPEC) — is used to treat ovarian cancer metastases, for example.

Hyperthermia is typically done within about an hour of chemotherapy, except in HIPEC, where patients receive hyperthermia and chemotherapy at the same time.

What it feels like

The beauty of hyperthermia is that doesn’t harm normal cells and tissues. However, Dr. Yu’s patients often question whether hyperthermia might burn.

“Hyperthermia often feels like a heating pad. Most patients do not find it uncomfortable,” she says.

Wire thermometers are used so doctors can monitor temperatures and prevent overheating.

Yet even with this precaution, about 10 percent of hyperthermia patients develop temporary skin blisters. These typically heal quickly, she says.

What the research shows

In 2010, Duke University researchers found that adding hyperthermia to radiation treatment for breast cancer produced a 65 percent response rate, compared with a 42 percent rate for radiation alone.

“More recently, in a randomized clinical trial, researchers found that hyperthermia and radiation improved pain control for bone metastases, compared to radiation alone,” says Dr. Yu.

Researchers in her lab have also been exploring the potential of hyperthermia to treat cancer stem cells that promote the growth of brain tumors.

As time goes on, more and more studies will reveal the benefits of hyperthermia for those with cancer, Dr. Yu believes.

“Combining hyperthermia and radiation is a great treatment to consider if you have failed prior chemotherapy and radiation therapy,” she says.