Outcomes following liver SBRT for metastatic pancreatic cancer.

Abstract

418 Background: Traditionally, the role of localized therapy for metastatic pancreatic cancer (MPC) has been limited. However, with more effective systemic therapies, recent studies have explored a potential role for local therapies. We aimed to report outcomes following SBRT (stereotactic body radiation therapy) for liver metastases (LM) in setting of MPC and to identify predictors of response. Methods: 41 patients who underwent ablative RT to LM for MPC (2005-17) were retrospectively identified. Median RT dose was 50 Gy (range: 8-60 Gy), delivered in 5-6 fractions. Kaplan Meier method was used to calculate local control (LC), progression-free survival (PFS) and overall survival (OS). Univariate (UVA) and multivariate (MVA) Cox proportional hazards models were used to identify predictors of clinical outcomes. Results: Median follow up was 14.6 months. This cohort included 19 men and 22 women. 61% of pts had metachronous LM, 39% had synchronous LM. At time of RT, the treated lesion was stable /responding to chemotherapy (CTX) in 36.6% of pts; 46.3% were progressing with mixed response; 17% were off/refused CTX. Median number of prior CTX regimens was 2 (range: 0-5). Median number of LM was 1 (range: 1-4). Median pre-RT CEA was 7 ng/mL, median pre-RT CA19-9 was 354 U/ml. The 12-month outcomes were 75.8% LC, 16.5% PFS, and 36.3% OS. 8/41 (20%) patients were off CTX for ≥ 4 months. On UVA for LC, pre-RT CA19-9 (log10 scale) was associated with LC (HR 2.28, p = 0.03). Timing of LM, CTX response of LM, number of lesions, RT dose and CEA did not predict LC. On UVA for PFS, extrahepatic disease at time of RT was associated with worse PFS (HR: 2.47, p = 0.04), and response to CTX (progressive vs. stable/responding) approached significance (HR 1.83, p = 0.10). On UVA for OS, lower pre-RT CEA (HR 1.009, p = 0.03), lower pre-RT CA19-9 (HR 1.67, p = 0.01), and response to CTX (HR 6.42, p < 0.001) were associated with improved OS. On MVA for OS, response to CTX at time of liver RT remained significant for OS. Conclusions: SBRT of LM for MPC offers high rate of LC. In a small subset of patients, SBRT to LM may offer prolonged duration off systemic therapy. Lower pre-RT CA 19-9 and CEA, absence of extrahepatic disease, and stability/response of CTX at time of liver RT may select for patients most likely to benefit.