SABR Offers Acceptable Side Effect Profile, Efficacy for Primary RCC

For patients with primary renal cell carcinoma (RCC) who are ineligible for surgical resection, stereotactic ablative body radiotherapy (SABR) serves as a non-invasive alternative with an acceptable side effect profile.

The FASTRACK II study, led by Shankar Siva, MBBS, PhD, and colleagues, examined the efficacy of this novel treatment in a phase 2 international trial.

The trial was conducted in 7 treatment centers throughout Australia and 1 in the Netherlands. Seventy patients were enrolled and initiated treatment between July 2016 and February 2020. Each eligible patient had a biopsy-confirmed diagnosis of primary RCC with a single lesion and had declined surgery, were medically inoperable due to a high risk of complications, or had an Eastern Cooperative Oncology Group performance score of 0-2.

Patients were administered either a single fraction SABR of 26 Gy for tumors less than 4 cm in maximum diameter or a single fraction of 42 Gy for tumors larger than 4 cm to 10 cm in maximum diameter.

The primary endpoint was local control, defined as no progression of the primary RCC, as evaluated by investigators according to the Response Evaluation Criteria in Solid Tumors version 1.1.

The median age of the patient group was 77 years, and the median tumor size was 4.6 cm. Before trial enrollment, 49 (70%) of the 70 patients had documented serial growth on initial surveillance imaging. Each enrolled patient had T1-T2a and N0-N1 disease. Twenty-three patients received single-fraction SABR of 26 Gy, while 47 patients received 42 Gy in 3 fractions. The median follow-up was 43 months.

At 12 months, local control from treatment commencement was 100% (P<.0001). Grade 3 treatment-related adverse events (TRAEs) occurred in 7 (10%) patients, consisting of nausea or vomiting in 3 patients; abdominal, flank, or tumor pain in 4 patients; colonic obstruction in 2 patients; and diarrhea in 1 patient. No grade 4 TRAEs were observed.

The FASTRACK II study is the first multicenter prospective clinical trial of non-surgical definitive therapy in patients with primary RCC. Treatment with SABR served as an effective treatment strategy, offering no local failures or cancer-related deaths.

With an acceptable side-effect profile and renal function post-treatment, the trial outcomes support further investigation into the use of SABR for primary RCC.