Stereotactic Body Radiotherapy Provides Excellent Long-Term Local Control of Very Few Lung Metastases

Discussion

Due to improved treatment of primary tumors and regional lymph nodes, the survival times of patients with cancer have become considerably longer over the past decades. Since the risk of developing metastatic disease increases with lifetime, the number of patients living long enough to experience the occurrence of distant metastases is constantly growing. This applies also to patients developing lung metastases. In cases with very few pulmonary lesions, more aggressive treatment regimens including surgical resection and SBRT have gained importance. In many centers, thoracic surgery is the first choice for these patients if they are considered able to withstand this procedure (1, 5). Patients with a reduced general condition and elderly patients are at a higher risk of experiencing surgery-related and anesthesia-related complications, including infections, pneumonia and thromboembolic events. Many such patients are referred for SBRT (2, 6). These selection processes likely led to biases in the past and have given the impression that SBRT is less effective than surgical resection. The present study of SBRT for 1-3 lung metastases included a considerable proportion of patients with a good performance status (ECOG 0-1) and patients younger than 70 years. According to the results, SBRT resulted in excellent long-term local control rates. At 2 and 3 years following SBRT, local control rates were still 93% and 78%, respectively. The 2-year local control rate of the present study was better than the local control rates of 64% and 86% observed in two previous studies (2, 6). This difference was likely due to the number of lesions and the primary tumor types included. In one previous study, up to five lung metastases were treated (2), and the other previous study focused on lung metastases from sarcomas that are considered less radiosensitive than many other solid tumor types (6). In the present study, the high local control rates did not translate into high overall survival rates. The 2-year overall survival rate of 56% was in the range of 49% to 66% of the previous studies (2, 6).

In the present study, the relatively low survival rates (in comparison to the high local control rates) can be explained by the fact that a considerable number of the patients showed progression of their disease distant from the irradiated lung metastases. At 2 and 3 years following SBRT, only 38% and 29% of patients, respectively, had no distant progression. This demonstrates that the patients included in this study still had less favorable characteristics than most patients included in studies investigating surgical resection of lung metastases. Despite the less favorable characteristics of the patients in the presents study, SBRT resulted in high long-term local control rates and can therefore be considered a reasonable option for all patients with very few lung metastases, not only for elderly patients aged 70 years or more and those patients with a poor performance status. Furthermore, SBRT for lung metastases was very well tolerated in the present series, with a comparably low pneumonitis rate (7). The results of SBRT, in particular regarding freedom from distant progression and overall survival, may be further improved with the addition of concurrent and sequential chemotherapy. The combination of SBRT and concurrent chemotherapy was recently presented as a new and feasible treatment option for metachronous primary lung cancer (8).

In conclusion, when administered for a very limited number of lung metastases SBRT resulted in excellent long-term local control rates and was associated with very little toxicity. Therefore, SBRT can be considered a reasonable alternative to thoracic surgery, not only for elderly patients and those with a limited general condition.