Session Item

Patients with oligometastatic disease (OMD) treated with metastasis-directed local therapies (MDT) such as stereotactic body radiotherapy (SBRT) are at a high risk of developing new metastases, which might be amenable to repeat SBRT. Subgroup analyses of recent clinical trials indicate that repeat SBRT after disease progression might be crucial to derive a survival benefit. Here, we explore oncological outcomes of OMD patients treated with repeat SBRT and compare these to patients having received a single course of SBRT.

OMD patients with 1-5 metastases from solid organ malignancies, treated with SBRT to all lesions were included in this retrospective study. Patients were classified by the number of SBRT courses as MDT to all lesions (single vs repeat SBRT). Progression-free survival (PFS), widespread failure-free survival (WFFS) with >5 metastases, overall survival (OS), systemic therapy-free survival (STFS; only patients with oligorecurrent disease) and the cumulative incidence of first failure was analyzed. Patient and treatment characteristics at baseline and disease progression predicting the use of repeat SBRT were investigated using multiple logistic regression.

Among 385 patients treated with SBRT for OMD, 129 (33.5%) were treated with repeat SBRT while 256 (66.5%) received a single course. The most common primary tumor was lung cancer (repeat: 34.1%; single: 35.2%), and the most common OMD state was metachronous oligorecurrence (repeat: 24.0%; single: 23.8%).
Patients treated with repeat SBRT had significantly shorter PFS (p<0.0001; Fig. 1A). Distant metastases as first failure were more frequently observed in repeat SBRT patients (p<0.0001; Fig. 2). Yet, patients treated with repeat SBRT more often presented with only a single metastasis at distant failure (repeat: 40%, single: 22.2%, p=0.003). However, WFFS was comparable in both groups (p=0.47; Fig. 1B). Among patients with oligorecurrence, no difference in STFS was observed between repeat and single course SBRT patients (p=0.22; Fig. 1C). Median OS was longer in repeat SBRT patients (p=0.01). On multivariable analysis, a higher number of previous lines of systemic therapy (1 line: odds ratio [OR] 2.68, p=0.002; 2 or more lines: OR 2.42, p=0.009) and low distant metastasis velocity (DMV) of <0.5 metastases per month at first distant failure (OR 3.27, p<0.001) were significantly associated with the use of repeat SBRT.

Despite shorter PFS, patients treated with repeat SBRT had comparable WFFS and STFS, and longer OS than patients receiving a single course of SBRT. A higher number of systemic therapy lines and a low DMV seemed to be correlated with repeat SBRT. Prospective investigation is required, preferably in a randomized setting, focusing on predictive factors to select patients that might derive a benefit from repeat SBRT.