Proposing synchronous oligometastatic non–small‐cell lung cancer based on progression after first‐line systemic therapy

Despite the importance of accurate disease definitions for effective management and treatment decisions, there is currently no consensus on what constitutes oligometastatic non–small‐cell lung cancer (NSCLC). Predominant patterns of initial progressive disease (PD) after first‐line systemic therapy have been shown to be a substantial basis for local ablative therapy (LAT) for all disease sites in patients with oligometastatic NSCLC, suggesting that these patterns could be helpful in defining synchronous oligometastatic NSCLC. Therefore, this retrospective study aimed to propose a threshold number of metastases for synchronous oligometastatic NSCLC, based on the pattern of initial PD after first‐line systemic therapy. The cut‐off threshold number of metastases compatible with synchronous oligometastatic NSCLC was determined using receiver operating characteristic (ROC) curve analyses of PD at the initially involved sites alone. ROC analysis of 175 patients revealed that the presence of 1‐3 metastases before first‐line treatment (sensitivity, 85.9%; specificity, 97.3%; area under the curve, 0.91) was compatible with oligometastatic NSCLC, therefore we divided patients into oligometastatic NSCLC and non‐oligometastatic NSCLC groups. Multivariate logistic regression analyses revealed oligometastatic NSCLC to be the only independent predictor of PD at initially involved sites alone (odds ratio 165.7; P < .001). The median survival times in patients with oligometastatic or non‐oligometastatic NSCLC were 23.0 and 10.9 mo (hazard ratio, 0.51; P = .002), respectively. Based on these findings, we propose synchronous oligometastatic NSCLC as 1‐3 metastases in accordance with patterns of initial progression. The result of our study might be contributory to provide a common definition of synchronous oligometastatic NSCLC.