Liver metastases are common in patients with neuroendocrine neoplasms. The role of stereotactic ablative radiotherapy (SABR) is not well understood in this population.

To evaluate the safety and efficacy of SABR in treating well-differentiated neuroendocrine liver metastases (WD-NELM).

A retrospective review of patients with WD-NELM treated with SABR between January 2015-July 2019. Demographic, treatment and clinical/radiographic follow-up data were abstracted. RECIST 1.1 criteria were applied to each individual target to evaluate the response to treatment. Local control (LC) and progression free survival (PFS) were determined using Kaplan-Meier methodology. Toxicity was reported according to CTCAE v5.0.

Twenty-five patients with a total of 53 liver metastases treated with SABR were identified. Most patients (68%) had midgut tumors, were Grade II (80%) and had high volume intrahepatic and/or extrahepatic disease (76%). Median number of liver metastases treated was 2 with a median size of 2.5 cm. Median radiation dose delivered was 50Gy/5 fractions. Median follow-up was 14 months; 24 of the 25 patients were alive at time of analysis. The objective response rate (ORR) was 32%, with improvement or stability in 96% of lesions treated. The median time to best response was 9 months. The 1-year LC and PFS were 92% and 44% respectively. No Grade III/IV acute or late toxicity was identified.

Liver SABR is a safe and promising means of providing local control for WD-NELM. This treatment modality should be evaluated in select patients in concert with strategies to manage systemic disease.