Phase II Clinical Trial Evaluating Complete Metastasis Ablation After Progression on Checkpoint Inhibition

Purpose/objective(s) Retrospective and prospective studies in patients with oligometastatic non-small-cell lung cancer (NSCLC) suggested clinical benefit after complete metastatic ablation (CMA). So far, no studies have addressed the toxicity and efficacy of CMA to oligometastatic lesions in patients that progressed during immune checkpoint inhibitors (ICIs) therapy. Here, we report results of a single arm- radiotherapy (RT) to oligometastatic lesions from our ongoing phase II trial (NCT02710253). Materials/methods This study enrolled patients that progressed within 6 months of ICI therapy and developed oligo-metastases. Treatment intervention allowed for any dose and fractions of RT per the treating physician to all metastatic sites, with irradiation for up to 6 sites. Primary endpoints of this study are time to new lesion development, and disease control rate (DCR) by RECIST 1.1. Secondary endpoints are toxicity, progression-free survival (PFS), overall survival (OS) and absolute lymphocyte counts (ALC). Results Of the 30 patients initially enrolled in this study, 26 patients (N = 21 NSCLC; N = 5 melanoma) were included in the analysis as they had completed imaging follow-up. A total of 64 lesions were irradiated with a mean of 2.5 lesions per patient. Most frequent location of irradiated was lung (n = 45), followed by adrenal (n = 7), liver (n = 4), bone (n = 4) and others (n = 4); 50% of patients received SBRT. At a median follow-up time of 23.0 months (range, 5.0-44.7 months), 12 patients had no new lesions, while 14 patients developed new lesions in lung (50%), bone (25%), brain (21%). Median time to new lesion development was 14.6 months. DCR was 77% (complete response 19%, partial response 19%, stable disease 38%); median PFS was 10.1 months and median OS was not reached. No toxicities greater than grade 2 was observed. Pre-RT ALC is an independent risk factor for time to new lesion development (P = 0.006, HR = 0.1, 95% CI, 0.02-0.51). Patients without new lesion development had significantly higher baseline ALC (P = 0.011) and more ALC after RT at 1 month (P = 0.025), 3 months (P = 0.006), 6 months (P = 0.002) and 12 months (P = 0.045) compared to patients with new lesions. Other factors including age, gender, SBRT, baseline tumor size, performance status and tumor histology did not affect the time to new lesion development. Conclusion In patients with oligometastatic lesions that progressed on ICI, CMA may be a valid treatment option that generates clinical benefits. By eradicating gross sites of disease by converting area sites into in-situ vaccines, T cells are able to access microscopic metastasis. Larger randomized trials are indicated to further define the role of CMA for ICIs resistance.