Advances in Renal Ablation

The landscape for renal ablation is changing as new studies suggest that certain patients may have outcomes comparable to surgery. With guidelines beginning to reflect those changes, interventional oncologists should be prepared to offer ablation alongside surgery to the proper patients, and to document proficiency and good outcomes. Matthew Callstrom, MD, PhD, explains the data underlying this shift and offers advice on preparing to treat more patients with ablation. Dr. Callstrom is a professor of radiology at the Mayo Clinic in Rochester, Minnesota and is on the board of the Society of Interventional Oncology. He presented on renal ablation as part of Craftsman’s Corner at the Symposium on Clinical Interventional Oncology.

Can you tell me about some recent data on renal ablation? 

There has been a good deal of data published on treatment of small renal masses, and the literature shows positive outcomes treating T1a lesions. My group published a collaborative paper led by Houston Thompson, MD, who is a urologist, and Thomas Atwell, MD, who is an interventional oncologist, with single-center data in which there was no statistical difference between treating patients with small masses with cryoablation versus partial nephrectomy. These data show that patients have a choice in treatment. Our practice will offer treatment of small renal masses of both percutaneous ablation and partial nephrectomy because the outcomes are essentially equivalent. With clinical T1a lesions, the local recurrence rates at 3 years of follow-up with cryoablation and partial nephrectomy are about 2%, so that means 98% of the time we get control of the tumor.

The guidelines are starting to suggest that renal ablation should be considered with a partial nephrectomy as an option for patients, which is a big shift. Over the next few years, I believe that patients will have surgery if it is appropriate, but they can have the expectation of a good outcome if they elect to have ablation. These good outcomes have been seen in multiple centers, so the success extends beyond high-volume centers.

We’re also seeing patients who have T1b lesions. In our single-center report, we also found equivalent outcomes for those patients with 4 to 7 cm diameter tumors. Many of those patients were not eligible for surgery, but they did well with ablation.

Do you have any tips for operators taking on these cases?

There are several different technologies for treating masses, and a very experienced operator is key for all of them. Operators need to have their outcomes be comparable with surgery, and the procedure must be done safely.

What does the learning curve look like for ablation procedures?

The learning curve is not steep for cryoablation because you can see what’s happening during the procedure. If you are able to effectively cover the tumor, your outcomes should be good. You likely will not injure the patient as long as the ice doesn’t extend into the nearby normal tissues such as the bowel, or get into the body wall or the collecting system.

The learning curve for heat-based systems in larger tumors is steeper if treating larger tumors. When using a heat-based approach, you need to know the diameters you expect to achieve based on your devices in order to avoid unexpected outcomes.  

What are your thoughts on the value of biopsy?

Most centers now are trying to biopsy the lesions that they’re treating. It is reasonable to either obtain tissue in advance of treatment or to biopsy at the time of the ablation. Either approach  is fine as long as your yield of the biopsy is sufficient to obtain the histology for the tumors that you’re treating. There may be differences in response based on the different types of histologies that we’re treating.

Do you have any advice for selecting the appropriate patients for ablation?   

I think the landscape is changing on the basis of several factors. We are beginning to approach the treatment of masses in younger patients on the basis of whether it is technically straightforward to treat with surgery or ablation on the basis of similar outcomes for ablation and surgery. Historically, we have been treating patients who are not surgical candidates, but at our center these patients are now being offered surgery, partial nephrectomy, or ablation as options, as long as the tumor is small. The patients are presented with the existing data so they can make an informed decision.

If operators are proficient and are diligently tracking outcomes in order to accurately represent their center’s success rates, I think it is appropriate to further develop the relationship with the urology team to consider offering ablation to younger patients, those who would classically have been the surgical population.

Do you have a case that illustrates an important teaching point to remember regarding renal mass ablation?

Most centers still offer a nephrectomy if a patient has a tumor. With a nephrectomy, the patient is left with one kidney, and quality of life is impacted if renal function is poor. Preservation of the renal parenchyma is an important strategy and is why partial nephrectomy was developed. If an individual loses renal function over time based on other medical issues, quality of life would be impacted unnecessarily by removing a kidney for a small renal mass. Both partial nephrectomy and ablation help to preserve function.

Some patients may have a solitary kidney, perhaps because they already had a tumor on the other kidney. If they develop a new tumor on the remaining kidney, what can we do? The approach of parenchymal-sparing treatment, using either ablation or partial nephrectomy in this instance, is very effective.

The risk of a patient needing dialysis after ablation is extremely low, so this approach is a way of preserving function. It’s unfortunate how many patients will show up with a new tumor after having been treated at other centers 5 to 10 years ago. We treat a significant population of patients who have solitary kidneys with a new renal mass.

Do you have any tips for managing and preventing potential complications from ablation?

The recovery time from a nephrectomy is about 3 to 4 days in the hospital, with a total recovery of 3 to 4 weeks. It’s major surgery, and the cost is significant. Additionally, the complication rate for everything related to the surgery, including bowel dysfunction, is around 15%.

With a partial nephrectomy, the hospital stay is likely decreased by one day and the recovery time is probably halved. The cost is about the same, but the risk profile is slightly higher. About 20% of patients will have some minor or major complication related to the procedure.

On the other hand, patients treated with ablation could be released on the same day, or stay one day in the hospital after treatment. Their recovery time is often related to anesthesia, so a patient is typically back to baseline in the 2 to 3 day timeframe. Many patients will go back to work in the same week. The cost is about one-third of that of surgery, and the risk profile is largely due to bleeding. With cryoablation, the risk profile is about 4%.

Are there any differences of opinion between colleagues in the field?

There is a need to obtain significant data on ablation beyond single-center data. We need a broader perspective of how centers perform in the treatment of these small masses. The question we need to answer is, if somebody shows up in some other center, are those results translatable? It’s up to the field to construct a registry or a trial that establishes what those outcomes would be across multiple centers.

What are some cases that you are excited to share with CIO attendees?

I’ll show examples of treatment of tumors in more difficult locations and how to avoid bleeding. Locations more central or adjacent to the ureter can be more challenging to treat. You need to understand how aggressive you can be with treatment without causing complications. It’s important to both know your device and to develop experience.

As new devices become available, you need to understand the strengths and weaknesses of them. Heat-based approaches such as microwave are a faster technology than cryoablation, but with that power comes the need for understanding the risk profile of those devices.

Is it difficult to choose the best device for a procedure?

The problem comes down to how much experience people can gain with different devices based on the volume of patients in their practice. We are fortunate to have a high-volume practice, so we can learn about systems safely because we can apply them to relatively simple cases initially. As operators gain experience with the device, they become more and more safe with the use of that device and more effective in terms of outcome. Choosing the best device is based on the tumor to treat and the experience of the proceduralist. An experienced person can do well with the same device that an inexperienced person could perform poorly with, purely based on judgment decisions derived from experience.

What are the important takeaways for practitioners?

The guidelines are beginning to consider offering of ablation alongside surgery. Thus, everyone who is treating patients with renal masses should be prepared to offer ablation, when appropriate, and to do it well.

You need to develop relationships with referring providers and be prepared to demonstrate with data that you have good outcomes. Additionally, it’s important to be more than a proceduralist. You have to be part of the whole practice, engaged in understanding the relative value of ablation relative to surgery, including the appropriate follow-up, etc. You need to cover the entire spectrum of the care of these patients to be considered an appropriate provider for treatment.

—Interview by Lauren LeBano