Lung cancer has always been a major challenge for human health. Many patients have advanced lung cancer by the time they are diagnosed, which brings serious economic and social burdens at the same time. Early lung cancer is mainly treated by surgery[12], but surgery cannot be performed for patients with advanced lung cancer. Traditional radiotherapy and chemotherapy are faced with a series of adverse effects, such as radiation pneumonia and bone marrow suppression. Despite the rapid development of targeted therapy and immunotherapy in recent years, expensive drugs are beyond the reach of patients in developing countries. Nevertheless, it remains the leading cause of cancer death and the median OS has not improved significantly[13, 14]. In recent years, many studies have shown that RFA is a feasible and safe treatment for patients with inoperable early lung cancer, lung metastases and patients with advanced lung cancer.
The median OS of patients in the present study was 22 months. The 1-year survival rate was 81.28% in patients in the early stage. A recent meta-analysis of surgical resection versus CT-guided percutaneous ablation for stage I NSCLC showed that there were no significant differences in 1–5-year OS or cancer-specific survival between surgery and ablation. However, the difference in early disease-free survival was significant. Therefore, RFA is an effective treatment for patients with inoperable stage I NSCLC[12].
MWA cannot be ignored for thermal ablation of tumors. The principle of MWA is different from that of RFA. MWA inactivates tumors by microwave energy[15]. There is still controversy about the efficacy of the two techniques in treating lung cancer. A previous study has suggested that MWA can be used for a wider range of indications with larger-diameter lesions than RFA can[16, 17]. In the present study, the maximum diameter of the lesion for RFA was 4 cm. Other studies have shown that patients with lesion diameter <3 cm treated with RFA can achieve long progression-free survival (PFS) and OS[18]. Xu Feng’s study[19] proved that the local tumor control rate (90.6% vs 78.1%) and PFS (10.4 vs 9.2 months) of MWA were better than those of RFA (P<0.05), and the OS was different (MWA vs RFA, 15.2 vs 14.6 months) (P>0.05). There was no significant difference in disease control and objective response rates. Nevertheless, a meta-analysis[20] showed that the OS rate of RFA-treated patients was higher than that of MWA-treated patients. In addition, median survival of patients with lung metastases treated by RFA was higher than that of patients treated with MWA. Nevertheless, MWA was superior to RFA in PFS rate and local tumor PFS rate, without a significant difference, except for 3-year progression-free survival rate (P=0.028). Therefore, multicenter, large-sample studies are needed to compare the clinical efficacy between RFA and MWA.
We found that, in patients with lesions <2 cm in diameter, combined chemotherapy/targeted therapy improved prognosis, while patients with elevated serum CEA before RFA had poor prognosis. In line with previous research, post-ablation therapy has a significant impact on the survival, and combination of multiple treatments is more effective. Xu et al.[21] proved that patients treated with RFA combined with chemotherapy fared better than those treated with RFA alone, with increased PFS and OS. Serum tumor marker levels decreased significantly after treatment. Besides, it is noteworthy that the effect was better in patients with lung adenocarcinoma than in patients with squamous cell carcinoma/small cell lung cancer. In contrast, different age and clinical stage of patients in our study had no significant effect on survival, which was not consistent with previous studies. This may have been related to the small sample size in our study. Also, some patients with advanced lung cancer were young and sought active treatment, which may have affected the results.
RFA is an effective palliative treatment for patients with inoperable advanced lung cancer. Many patients suffer from cancer pain and have to take opioids for pain relief for a long time. A new study showed that RFA can relieve cancer pain in patients with advanced lung cancer by 70%[22], and can also reduce the frequency and dose of opioids, thereby improving the quality of life of patients with advanced lung cancer. We did not study remission of cancer pain, which can be followed up in the future.
Related studies have shown that the complications of RFA of lung cancer are divided into two types; one is puncture-related and the other is melt-related. Pulmonary hemorrhage, hemothorax and pneumothorax belong to puncture-related complications. Pleural reaction, skin burns and chest pain pertain to melt-related complications[23, 24]. These complications can be resolved by symptomatic treatment, and the possibility of a fatal complication is extremely low. In the present study, the rate of complications was 44.12% (15/34), which is higher compared with previous studies[25, 26]. The most common complication during RFA was pleural effusion. In addition, chest CT re-examination after ablation showed spontaneous absorption of pleural effusion without therapeutic drainage. Therefore, RFA is a safe treatment. In the future, we should pay more attention to the position and angle of needle insertion to avoid unnecessary injury. We demonstrated that smoking history was a risk factor for complications, which may be related to structural pulmonary lesions such as emphysema caused by long-term smoking. However, there was no relationship between age, gender, lesion size, lesion location and complications. In the future, we need a larger sample of cases.
There were several limitations to our study. First, our hospital has carried out RFA for lung cancer since 2013. Up to now, a total of 67 cases have been successfully performed, which included patients with lung metastases and irregular follow-up, and only 34 cases have met the inclusion criteria, and only 29 patients were followed up. The overall number of cases was low, and it may reduce the statistical power and affect the reliability of survival data. Therefore, further data collection is required to expand the sample size to verify the efficacy of RFA for lung cancer. Second, many patients were not followed up for chest CT in our hospital, on the grounds that it was different to collect chest CT data, so we were not able to analyze the local PFS of patients. Third, we did not compare the efficacy of RFA combined with chemotherapy and intravenous chemotherapy alone, which would be important for exploring whether RFA and chemotherapy have synergistic effects. We will continue to follow up more patients to better understand the long-term prognosis of RFA.