Kidney cancer has long been thought of as unresponsive to radiation. But that’s not always the case.
It’s true that kidney cancer doesn’t respond well to conventional, low-dose per treatment radiation therapies. But we’ve found that the disease is sensitive to a type of high-dose per treatment radiation therapy known as stereotactic radiotherapy.
While stereotactic ablative radiotherapy (SAbR), also known as stereotactic body radiation therapy (SBRT), has been used for other types of cancer for some years now, it’s been underutilized for kidney cancer treatment due to the radiation-resistant misconception. UT Southwestern Medical Center is one of the few locations in the country to offer this option for kidney cancer patients, and the results have been promising.
How stereotactic radiotherapy works
With SAbR, we use imaging technology to target a high dose of radiation onto a specific tumor located anywhere in the body. This kills the tumor while limiting the amount of radiation the surrounding healthy area receives. In fact, an area 4 mm – or the thickness of two nickels – from the tumor would get minimal radiation and may not be damaged.
I would compare stereotactic radiotherapy to a noninvasive form of surgery. Rather than using a blade to cut out a precise section of cancer cells, we use highly targeted radiation.
One of the great advantages to the patient is how little time it takes to get SAbR. Conventional radiation therapies are given in daily sessions over up to eight weeks. But with SAbR, high-dose radiation is generally given in just one to five sessions. This can be especially important for patients traveling far from home for treatment.
Another perk is that because fewer healthy cells are affected, SAbR has few side effects. Fatigue is the most common side effect our patients report which happens in less than 10 percent of patients.
How we use SAbR to treat kidney cancer
SAbR currently is available as a treatment option for kidney cancer patients who are not healthy or strong enough for surgery. But we are participating in clinical trials to establish the effectiveness of SAbR in other situations related to kidney cancer, including:
Primary tumor removal
The standard of care for tumors contained within the kidney (stage 1 kidney cancer) is to remove the tumor with surgery, a procedure called a nephrectomy, which removes the entire kidney, or partial-nephrectomy, which removes part of the kidney. We are looking at whether SAbR can be used in lieu of surgery to destroy the tumor. Trial participants are showing a good early response in that the tumor is being eliminated with SAbR alone.
Metastatic kidney cancer
If the primary tumor in the kidney is removed but the cancer has spread (or metastasized) to other parts of the body, we’re finding stereotactic radiotherapy methods such as Gamma Knife and CyberKnife are effective in killing off tumors in sites such as the brain and spine. In addition, we have found that if the metastasis is limited to an organ such as a lung, liver, bone, or lymph node, it can be successfully eradicated with SAbR.
A study we published in May 2017 found that SAbR achieved more than 90 percent control of metastases in these settings. We also found that SAbR can be used to delay the start of chemotherapy and other systemic therapies. Systemic therapies deliver drugs throughout the body to kill cancer cells wherever they may be. These therapies can cause significant side effects, such as fatigue, hair loss and cell damage, which can affect the quality of life.
Sometimes, one or more sites of metastases develop resistance to systemic therapy and resume growing while other sites respond to the therapy. This is known as oligo-progressive disease. We’re evaluating the effectiveness of using SAbR on those few sites while allowing patients to continue with the systemic therapy. The benefit of this is not having to try a new systemic therapy to which patients may not respond or that may cause side effects. I think these uses of SAbR will become routine in the future.
IVC tumor thrombus
Up to 10 percent of patients with renal cell carcinoma, the most common form of kidney cancer, develop a complication known as inferior vena cava (IVC) tumor thrombus. This occurs when the tumor grows into the inferior vena cava, a large vein that brings blood from the lower body back to the heart. Renal cancer is one of the few known cancers that grow into the veins. When this happens, the blood can spread cancer cells throughout the body.
We know that about 70 percent of patients who undergo surgery with IVC tumor thrombus will eventually develop metastatic cancer. We’re looking at whether using SAbR before surgery can kill those cancer cells and significantly decrease the risk of metastasis.
We’ve found that stereotactic radiotherapy not only kills the tumor we have treated but also alarms the body’s immune system about the tumor, which can lead to the development of an immune response to the tumor. We’ve seen this immune response firsthand. We used SAbR on the primary tumor of a patient whose kidney cancer had spread. Not only did the primary tumor shrink, but secondary cancer sites also regressed —an effect called the abscopal effect of radiation therapy. SAbR acts almost like a vaccine by teaching the body’s immune system to find cancer cells and kill them.
Stereotactic radiotherapy’s immunogenic property also can be harnessed by adding it to the existing immunotherapies for kidney cancer. We call this approach the i-SAbR regimen.
While SAbR is relatively new to the field of kidney cancer, it’s showing tremendous promise for our patients. Request an appointment to see if SAbR is an option in your kidney cancer treatment.