SABR: Strong Contender for Treating Solitary Kidney Cancer

Pam Harrison

October 26, 2018

SAN ANTONIO — Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy (SBRT), is emerging as a strong contender for the treatment of solitary-kidney renal cell carcinoma (RCC). The technology offers excellent local control that persists for at least several years, and it has little effect on kidney function, according to the authors of the largest pooled analysis of solitary-kidney cancer patients yet compiled.

"Current management options for solitary-kidney RCC tend to be invasive, requiring either surgical or percutaneous access, and are limited in various ways, including tumor size and location," lead study author Rohann Correa, MD, PhD, London Health Sciences Center, Ontario, Canada, related at a news briefing here.

In contrast, SABR is a noninvasive, outpatient therapy that requires only a single or a few treatment visits.

"We found that SABR can provide excellent local control with an acceptable impact on renal function in patients with solitary-kidney RCC, and outcomes are comparable to SABR-treated patients with two kidneys," Correa observed.

The new study was presented here at the American Society for Radiation Oncology (ASTRO) 2018.

Correa and colleagues analyzed patient data from nine international institutions within the International Radiosurgery Oncology Consortium for Kidney group.

Of the 223 patients who underwent renal SABR, 81 had a solitary kidney.

Correa noted that a large proportion of patients with solitary-kidney RCC have late metastases from their original RCC for which they had previously undergone nephrectomy.

The mean age of the solitary-kidney RCC cohort was 62.5 years, 69% were men, and almost all patients had a good performance status.

Patients with solitary-kidney RCC had slightly smaller tumors, at 3.7 cm, compared to patients with both kidneys, whose tumors measured 4.3 cm (P < .001), the investigators note.

The median total dose delivered in the solitary-kidney cohort was 25 Gy, and the median number of fractions was only one, Correa pointed out.

Although both the total dose and the number of fractions were significantly lower in the solitary-kidney cohort than in the bilateral-kidney cohort (P ≤ .001), the median biologically effective dose was identical for the two cohorts, at 87.5 Gy.

At a median follow-up of 2.6 years, local control was achieved in 98% of patients with solitary-kidney RCC treated with SABR. Of the solitary-kidney cohort, 77.5% had not experienced disease progression at the same point in time.

However, moderate chronic kidney disease, as reflected by an estimated glomerular filtration rate (eGFR) of ≤60 mL/min/1.73 m2, was associated with a poorer progression-free survival (hazard ratio [HR], 2.66; P = .043).

Rates of cancer-specific survival in the solitary-kidney cohort were also high, at 98.2%, and 81.5% of patients with solitary-kidney RCC were still alive at follow-up.

The local control rate of 97.8% for patients who underwent treatment of both kidneys was comparable to that achieved in the solitary-kidney cohort. The cancer-specific survival in the bilateral-kidney cohort was 94.3%.

At follow-up, 82.4% of those with both kidneys were also still alive after SABR, Correa noted.

SABR and Kidney Function

The impact of SABR on kidney function, which is a top concern for patients who cannot compensate for any loss of renal function in their remaining kidney, was minimal.

At baseline, kidney function was slightly better for patients with solitary-kidney cancer, at a mean eGFR of 64.6 mL/min/1.73 m2 , compared to a mean of 57.2 mL/min/1.73 m2 for the bilateral-kidney cohort (P = .016).

After SABR treatment, both groups experienced a similar decline in eGFR. For the solitary-kidney cohort, the mean decrease in eGFR was 5.8 mL/min/1.73 m2, vs 5.3 mL/min/1.73 m2 for the bilateral-kidney cohort.

The investigators noted that tumor size >4 cm was associated with more significant decreases in eGFR following SABR (HR, 4.1; P = .029).

Most importantly, no patients in the solitary-kidney cohort required dialysis following treatment; by contrast, six patients in the bilateral cohort required dialysis.

Correa explained to Medscape Medical News that the standard of care for early or localized RCC is surgical extirpation; RCC of higher stages can be treated medically with a tyrosine kinase inhibitor.

The fact that SABR is totally noninvasive and appears to be able to overcome intrinsic radioresistance of RCC, which has been a problem with standard fractionation radiation therapy, makes SABR a very attractive treatment option for solitary-kidney RCC, he suggested.

"I think the data are very interesting and exciting, but this is a retrospective study, so I don't think we are ready to replace surgery yet," Correa cautioned.

"But for the right patient, for the right situation, SABR should be an option worthy of consideration," he concluded.

Session moderator Nela Vapiwala, MD, PhD, associate professor of radiation oncology, the Perelman School of Medicine at the University of Pennsylvania, in Philadelphia, said that "something as noninvasive as SABR that can preserve kidney function is very appealing, so not only can patients survive their cancer, but they can stay off dialysis."

She pointed out that dialysis can lead to many potentially fatal complications.

"This technology really goes beyond our immediate instinct to say, 'Well, it's noninvasive, let's use it,' " she added. "It's really about long-term implications, and I think the fact that SABR is convenient for patients, that it's safe, and that it compares well with other local treatments — I agree with Correa that this is where the field is now headed."

Dr Correa and Dr Vapiwala have disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 2018. Abstract 222, presented October 23, 2018

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