Margriet Kwint

Outcome of treatment of synchronous oligometastases 63 3 NSCLC. De Ruysscher et al. [11] reported a prospective single arm phase III study for synchronous oligometastatic disease. The median OS and PFS in this study were 13.5 months and 12.1 months, respectively. The PFS is comparable to our results. The OS reported by De Ruysscher et al. is considerably lower. A possible explanation for this difference may be the time cohort 2008 to 2016 as compared to 2006-2010 in the study of De Ruysscher, as 2 nd line systemic treatment in stage IV NSCLC patients has changed over recent years. Next to that, only 10% of our patient group received best supportive care (after progression), compared to 23% in the study by the Ruysscher et.al . The randomized study of Gomez et al. [14] reported a PFS of 12 months in the experimental arm (treatment with local consolidative therapy in patients without progression after first line chemotherapy) which is similar to our results. In our study population, at time of analysis, 5 patients (5%) were still alive 3 years after treatment without any signs of recurrence. De Ruysscher et al. observed that 15% of the patients did not show disease progression after 24 months. These data support the concept of oligometastatic disease in NSCLC and emphasize that these patients may be cured or have a favorable PFS. In the literature different patient and tumor related prognostic factors are described for prolonged OS. We found that a good performance score and non-squamous cell carcinoma are favorable prognostic factors of OS. These results are in accordance with the results of Griffioen et al [15] and Flannery et al. [13]. Griffioen reported a better OS in patients who underwent surgery of the primary tumor, a smaller PTV of the primary tumor and non-squamous cell carcinoma. Flannery reported a better OS in patients with a Karnofsky performance score ≥ 90. We acknowledge that the observational nature of this study has limitations. First, observational studies carry the risk of selection bias. There is a clear patient selection bias due to the procedure by selecting patients in a multidisciplinary tumor board meeting in a tertiary reference center which is obviously limiting the generalizability of our data. Only patients with favorable risk factors, like good performance score, no weight loss, few comorbidities and fit enough for chemotherapy, were selected for radical treatment. The majority of patients within our study population presented with adenocarcinoma (64%) and a single metastasis (85%). These are known favorable prognostic factors for oligometastatic NSCLC [7,9,15] and might have contributed to the favorable OS and PFS.