Prolonging utilization of systemic therapy in oligoprogressive metastatic renal cell carcinoma using stereotactic body radiation therapy.

Abstract

336 Background: SBRT in indicated for the management of locally recurrent and oligometastatic mRCC as per National Comprehensive Cancer Network guidelines. Our study evaluates both the efficacy of radiotherapy (RT) in prolonging systemic treatment along with RT toxicity in the oligoprogressive RCC setting. Methods: A single institution retrospective data collection was performed in which we identified mRCC patients who experienced oligoprogression (defined as <1 sites of progressive disease) while on an FDA approved systemic therapy and were concurrently treated with SBRT, while remaining on the same therapy. Clinicopathologic characteristics and SBRT-related data along with duration of systemic therapy (DOT) were collected. DOT was then quantified into two categories which included the duration of systemic therapy prior to oligoprogression (DOT[P]) and duration of systemic therapy after completion of SBRT (DOT[S]). The ratio of DOT[S]/DOT[P] was calculated to determine the impact of SBRT on systemic treatment prolongation. Results: 23 patients diagnosed with mRCC meeting criteria were identified, 91% (n = 21) with clear cell histology and 9% (n = 2) with papillary histology. At the time of oligoprogression, 15 patients (65%) were on immunotherapy, 7 patients (30%) were on targeted therapy, and 1 patient (5%) was on combination therapy. We noted the preponderance of patients were on a first-line therapy at the time of oligoprogression (n = 10, 43%). A median of 2 (range, 1-3) lesions were treated per patient, with lung being the most frequent site (n = 14, 40%). The median total dose of SBRT was 30 Gy (range, 27-50 Gy) with a median dose per fraction of 6 Gy (range, 3-12 Gy). SBRT related toxicities, all of which were grade <2, were noted in 5 patients (22%), of which fatigue was the most frequent side effect (n = 3, 13%). Median DOT[S] was 13.4 months (range, 0.5-37.7 months) and the median DOT[P] was 12.8 months (range, 0.4-46.3 months). Results demonstrated a median DOT[S]/DOT[P] ratio to be 1.3 (range, 0.01-25.8). Conclusions: Based on our data, we discovered the addition of SBRT to systemic therapy during oligoprogression is not only well-tolerated, but that this treatment had clinical benefit in prolonging time on systemic therapy for patients with mRCC. The utilization of SBRT may prolong lines of therapy, thereby decreasing additional toxicities associated with exposure to new regimens.