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Purpose: The oligometastatic state is a proposed entity between localized cancer and widely metastatic disease, comprising an intermediate subset of metastatic cancer patients. Most data to support locally-directed treatment, such as stereotactic ablative radiotherapy (SABR), for oligometastases are from retrospective institutional reports. Following the success of a recently completed and reported phase II trial demonstrating important clinical outcomes, herein we review the current landscape of ongoing clinical trials in this context. Materials and methods: A review of currently activated and registered clinical trials was performed using the clinicaltrials.gov database from inception to February 2019. A search of actively recruiting trials, using the key words oligometastases, SABR, and various related terms was performed. Search results were independently reviewed by two investigators, with discrepancies settled by a third. Data abstracted from identified studies included study type, primary disease site, oncologic endpoints, and inclusion/exclusion criteria. Results: Of the initial 216 entries identified, 64 met our review eligibility criteria after full-text review. The most common study type was a phase II clinical trial ( n = 35, 55%) with other study designs ranging from observational registry trials to phase III randomized controlled trials (RCTs). A minority of trials were randomized in design ( n = 17, 27%). While most studies allowed for metastases from multiple primary disease sites ( n = 22, 34%), the most common was prostate ( n = 13, 15%), followed by breast, gastrointestinal, non-small cell lung cancer (NSCLC), and renal ( n = 6, 9% each). In studies with a solitary target site, the most common was liver ( n = 6, 9%) followed by lung ( n = 3, 5%). The most common primary endpoints were progression-free survival (PFS) ( n = 20, 31%) and toxicity ( n = 10, 16%). A combined strategy of systemic therapy and SABR was an emerging theme ( n = 23, 36%), with more recent studies specifically evaluating SABR and immunotherapy ( n = 9, 14%). Conclusion: The safety and efficacy of SABR as oligometastasis-directed treatment is increasingly being evaluated within prospective clinical trials. These data are awaited to compliment the abundance of existing observational studies and to guide clinical decision-making.

The characterization and treatment of oligometastatic disease (OMD) are rapidly growing areas of research. Consensus statements have recently been developed by European Society for Radiotherapy and Oncology (ESTRO)/American Society for Radiation Oncology (ASTRO) and ESTRO/European Organization for Research and Treatment of Cancer (EORTC) in an effort to harmonize terminology describing OMD. The purpose of this study was to assess patient populations eligible for ongoing clinical trials evaluating stereotactic ablative radiotherapy (SABR) in OMD in the context of key definitions from both statements. Using the clinicaltrials.gov database, a search of ongoing OMD clinical trials evaluating the use of SABR was performed from inception to January 2020, using the keywords "oligometastasis", "stereotactic radiotherapy", and related terms. Results were independently reviewed by two investigators, with discrepancies settled by a third. Information from these trials including study design, population criteria, and primary endpoints were extracted. OMD was defined in general as a limited number of metastases that could be safely treated with metastasis-directed therapy. States of OMD were broadly categorized into de novo, repeat, and induced, with synchronous and metachronous being subsets of de novo. The initial search strategy identified 293 trials, of which 85 met our eligibility criteria. Phase II trials were by far the most common (n=46, 52%). Most trials had a single treatment arm (n=43, 51%), and 31 (36%) were randomized.The majority of trials (n=65, 76%) had populations that included all three subsets of OMD. Notably, 70 trials (82%) also included oligoprogressive disease, which is debatably a distinct entity from OMD. Progressionfree survival was the most common primary endpoint (n=31, 36%), followed by local control (n=17, 20%), toxicity (n=14, 16%) and overall survival (n=7, 8%). Although the use of SABR for OMD is an active area of prospective clinical trial research, ongoing studies include mixed populations as defined by new consensus statements. Therefore, the applicability of results from these trials should be considered within relevant OMD scenarios.

Patients treated with surgery for lung cancer are at risk of second primary lung cancers (SPLCs), which when localized, may be amenable to radical treatment. Treatment options, however, are limited due to reduced cardiopulmonary reserve and competing mortality risks. The aim of this study was to perform a systematic review of publications examining treatment planning considerations, clinical outcomes, and toxicity rates of stereotactic ablative radiotherapy (SABR) in patients who have previously undergone pneumonectomy. A systematic review of the literature was conducted in accordance with PRISMA guidelines using PubMed and EMBASE from inception to July 2018. Articles were limited to those published in the English language. Non-review articles with patients who received exclusively lung SABR post-pneumonectomy were included. Two reviewers independently performed abstract and full-text review, with discrepancies settled by a third reviewer. Of the 215 articles identified by the initial search, 6 articles comprising 53 patients who received lung SABR post-pneumonectomy met inclusion criteria. The mean age was 68, and most patients were male (73.7%). The mean time to pneumonectomy was 6.5 years. The mean biologically effective dose was 115 Gy, and the most common dose fractionation schemes were 54 Gy in 3 fractions, 48 Gy in 4 fractions, and 50 Gy in 5 fractions. The mean follow-up was 25.4 months. The mean 1-year overall survival and 2-year local control rates were 80.6% and 89.4%. Grade 3 or higher toxicity was reported in 13.2% of patients. SABR appears to be a safe and feasible option for SPLCs in patients with prior pneumonectomy. Multi-institutional and/or prospective studies would be helpful to determine the true risk and appropriateness of SABR in this high-risk patient population.

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