3203 - A Prospective Study of Stereotactic Body Radiotherapy in Oligometastatic Renal Cell Carcinoma

R. R. Katipally¹, G. Rajeev-Kumar¹, A. A. Solanki², F. Arif¹, S. E. Eggener³, R. Z. Szmulewitz⁴, W. M. Stadler⁴, R. F. Sweis⁴, S. P. Pitroda¹, and S. Liauw¹; ¹Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL, ²Department of Radiation Oncology, Loyola University Medical Center, Maywood, IL, ³Department of Surgery, Section of Urology, University of Chicago, Chicago, IL, ⁴Department of Medicine, Section of Hematology/Oncology, University of Chicago, Chicago, IL

Purpose/Objective(s): This prospective study was designed to evaluate the safety and preliminary efficacy of stereotactic body radiotherapy (SBRT) for oligometastatic renal cell carcinoma (RCC). It was hypothesized that SBRT would offer excellent local control with minimal severe toxicity, and potentially delay the need to initiate systemic therapy. Materials/

Methods: Patients with oligometastatic RCC (1-5 lesions = 6cm, = 3 brain metastases addressed prior to enrollment, no therapies in prior month) were treated with SBRT to all metastatic sites (40-50 Gy/5 fractions). The primary endpoint was the rate of grade 4+ adverse events (AEs) per CTCAE v4.0; the trial would test the null hypothesis of a 5% toxicity rate using a sequential toxicity monitoring schema (n=25). Secondary endpoints included local failure of treated lesions (LF), distant progression outside of the treated sites (DM), and progression-free survival (PFS). Exploratory endpoints included time to subsequent systemic therapy and metastasis-directed therapy. Overall survival (OS) and PFS were analyzed via the Kaplan-Meier method and other time-to-event endpoints were analyzed as cumulative incidence with death as a competing risk.

Results: 15 patients (median age 50 years, 33% female, all with resected primary tumors, 40% prior systemic therapy, 27% prior metastasis-directed therapy) received SBRT to 23 lesions (median 1 lesion, range 1-4; median BED₁₀ of 100 Gy; 43% lung, 35% abdomen, 17% bone, 4% head and neck). The trial was closed early due to slow accrual. With median follow-up of 4.8 years, there were no grade 3+ AEs and no late grade 2+ AEs attributable to SBRT. Five (33%) patients experienced 7 acute grade 2 AEs (nausea [n=2], vomiting, pneumonitis, numbness/tingling, back pain, and fatigue). Outcomes are presented in the Table below. LF occurred in one lesion (4.3% crude LF across lesions) in one patient; the dominant pattern of failure was distant. The cumulative incidence of subsequent systemic therapy was only 40% and 54% at 2- and 5-years, respectively. Additional ablative metastasis-directed therapy was utilized in roughly half of the patients, at a median time of 2.1 years.

Conclusion: Metastasis-directed SBRT for oligometastatic RCC is safe and associated with excellent local control. This prospective study adds to emerging data that SBRT may delay additional systemic therapy with a minimal risk of severe toxicity. A subset of patients with more favorable disease biology may benefit from additional local interventions, such as SBRT or surgery.

Abstract 3203 – Table 1

Endpoint	2 Yrs (95% CI)	5 Yrs (95% CI)
OS	100% (CI not evaluable; no events)	90% (47% to 99%)
PFS	46% (20% to 68%)	No patients evaluable; all patients were censored or experienced progression
LF	6.7% (0% to 26%)	6.7% (0% to 26%)
DM	41% (17% to 64%)	85% (53% to 96%)
Subsequent Systemic Therapy	40% (16% to 63%)	54% (27% to 75%)
Subsequent Metastasis-Directed Therapy	13% (2% to 35%)	52% (16% to 79%)