In spite of a relatively low frequency (3–7%)(5, 19, 20), liver metastasis (LM) is considered as the worst prognostic factor among all metastatic sites in NSCLC patients(3, 21). The estimated OS of these patients is usually less than 6 months(4, 5, 9). Thus, predicting individual survival is critical to personalize treatment strategies and improve physician-patient communications. In this study, a nomogram was built to assess OS probabilities of NSCLC patients with LM. Further analysis confirmed the predictive ability and clinical value of the model, which is of great significance for stratifying risk groups.
Our study revealed that sex, race, age, grade, and T stage were independent predictors of overall survival, which is consistent with prior studies(4, 16, 17). Notably, in addition to these classical risk factors, we found that in NSCLC patients with LM, the presence of bone or brain metastasis was significantly correlated with poor outcomes, whereas the impact of lung metastasis in the same group is negligible. Several reports have noted that the outcome among different metastatic sites varies(3, 21). Yang et al(22) pointed out that the prognosis in NSCLC patients with multiorgan metastases was substantially more unfavorable than those with single organ metastasis. All the evidence strongly supports metastatic heterogeneity in NSCLC. In terms of histologic types, our results found that the prognosis was better in adenocarcinoma than other subtypes of NSCLC, which was in line with earlier findings(16, 17). Nevertheless, histology surprisingly did not remain significantly statistically in the multivariate analysis. It has been reported that the survival benefit for adenocarcinoma was only observed in recent decades, indicating the increasing impact of molecular targeted therapy in adenocarcinoma patients(23). Unfortunately, recent studies demonstrated that LM was a negative prognostic factor in NSCLC patients receiving EGFR-TKIs therapy. Compared to NSCLC patients with an absent of LM, the treatment response was dramatically poorer in those with the presence of LM(6, 7). Therefore, the discrepancy in our study could be attributed to the liver resistance to the molecular target therapy.
As shown in the nomogram, chemotherapy contributed the most to the overall survival. In our study, the patients received chemotherapy had a much better prognosis than those without chemotherapy (7 months vs. 2 months, P < 0.001). Similarly, prior studies suggested that chemotherapy made a large contribution to the survival outcomes for NSCLC patients with brain or bone metastasis(24–26). Moreover, given that LM was significantly related to dismal prognosis in patients had targeted therapy and immunotherapy(6–11), chemotherapy still plays an essential role in the setting of liver metastasis.
The significance of local treatment in patients with metastatic NSCLC remains controversial. Current study revealed a survival benefit in patients with surgically treated NSCLC with LM. Of patients received resection of primary tumor, 71% treated with chemotherapy and 33% treated with radiotherapy, indicating that local resection was only a part of the multimodal therapy in most cases. David and colleagues also reported that the median OS time was significantly increased with surgical procedures in NSCLC patients with metastasis(27). Besides, they also stated that surgery might be considered as part of multimodality therapy, given the crucial role of systemic therapies. Of note, not all patients can benefit from surgery. Various individual and tumor-related risk factors should be taken into consideration when surgical treatment is performed in a multidisciplinary setting (28–30). Interestingly, our study found that radiotherapy, as another option of local treatment strategies, was not able to independently predict the OS in NSCLC patients with LM (P = 0.403). The role of radiotherapy in metastatic NSCLC has not been fully explored. Our data indicated that radiotherapy alone may have a modest impact on prognosis. However, it should be noted that the prognosis of NSCLC patients with LM is unfortunately dismal with a median OS of only 5 months. There might not be much of a chance to prove the value of radiotherapy in long-term prediction, due to a relatively long course of the treatment. Hence, Wallace and colleagues suggested that shorter courses of radiotherapy should be considered in patients with limited prognosis(31). Further, preclinical studies reported that radiotherapy induced T-cell infiltration and increased tumor antigen release, which leading to an enhancement of antitumor immune response(32–34). As a result, Corrao and colleagues implied that the survival outcomes in NSCLC patients with LM might be improved when radiotherapy combined with immunotherapy(35). Besides, for patients with severe pain or complications, radiotherapy may still be an option of palliative care.
Unlike bone or brain metastasis, limited data exist to look at liver metastasis of NSCLC. To date, this is the first study to establish a prediction model focusing on the overall survival of NSCLC patients with LM. By using this practical tool, physicians might be able to identify the subgroup patients that require more intensive treatments and needs closer attention.
Nevertheless, limitations should be admitted in this study. First, there was an inevitable selection bias resulting from its retrospective nature. Second, some detailed information on treatments, such as chemotherapy regimens, radiation dose, targeted therapy, immunotherapy, was not available in the SEER database. Similarly, the data of gene mutations, other metastatic sites including adrenal metastasis, performance status cannot be obtained. Third, our nomogram was only validated internally with a relatively small size cohort. An independent external cohort with a larger sample size is still required for future application. Finally, given that all enrolled records were from the United States, perspective global data is warranted to apply our model to the Asian population and patients worldwide.