Renal cell carcinomas (RCCs) are often localized and are commonly managed through active surveillance, surgery, or minimally invasive techniques. Hannan et al conducted a study to determine if stereotactic ablative radiation (SAbR) is effective for the management of primary RCCs. SAbR could potentially serve as a new noninvasive alternative treatment, but data on the procedure are limited.
A total of 16 patients were enrolled in the study. Each patient had biopsy-confirmed, radiographically enlarging, primary RCC (≤5 cm). The study’s primary end point was local control (LC), defined as a reduction in tumor growth rate compared with a benchmark of 4 mm/year on active surveillance, and pathologic evidence of tumor response at 1 year.
Secondary end points included LC as measured by the Response Evaluation Criteria in Solid Tumors (RECIST), safety, and preservation of kidney function. Further exploratory tumor cell-enriched spatial protein and gene expression analyses were conducted on pre- and posttreatment biopsy samples.
At 1 year, radiographic LC was observed in 15 (94%) patients and accompanied by pathologic evidence of tumor response such as hyalinization, necrosis, and reduced tumor cellularity in all patients. According to RECIST, 100% of the treatment sites also remained progression-free at 1 year.
The median pretreatment growth rate was 0.8 cm per year (interquartile range [IQR], 0.3-1.4), while the median posttreatment growth rate was 0 cm per year (IQR, –0.4 to 0.1; P<.002). Tumor cell viability decreased from 4.6% to 0.7% at 1 year (P=.004). With a median follow-up of 36 months for censored patients, the disease control rate was 94%.
SAbR was well-tolerated, with no grade ≥2 (acute or late) toxicities. The average glomerular filtration rate declined from a baseline of 65.6 ml/min to 55.4 ml/min at 1 year (P=.003). Spatial protein and gene expression analyses were consistent with the induction of cellular senescence by radiation.
The trial found SAbR to be a safe and effective noninvasive treatment option for patients with primary RCC.