At present, there is no uniform standard for the surgical method of MPLC. Some scholars [12-14] have reported that lobectomy should be the first choice for the second primary tumor, followed by segment or wedge resection. However, sublobectomy, including segmentectomy and wedge resection, has also been studied as the main surgical method [3, 15]. At the cost of damaging more pulmonary functional reserve compared with segmentectomy or wedge resection, lobectomy can remove more intrapulmonary lymph nodes and significantly reduce the recurrence rate of tumor , which can undoubtedly affect the postoperative quality of life of patients, especially those with history of lung cancer-directed surgery. For stage IA SP-NSCLC patients with previous lung cancer-directed surgery, to date, it has not been fully understood whether lobectomy is more conducive to survival than wedge resection. Although several retrospective studies [16-18] and a recent SEER-based study  have found that lobectomy did not show a significant survival advantage over sublobectomy for SPLC patients, these researches still lacked an in-depth study on SPLC patients who have undergone radical surgery for primary lung cancer. To better solve this problem and provide references for further clinical research and practice, we carried out this study.
In the present study, wedge resection demonstrated equivalent OS to lobectomy, both before and after PSM. Similar results were observed in all clinical subgroups. Unlike the previous studies [4, 15, 19, 20], participants in this study were patients with stage IA SP-NSCLC with with previous NSCLC resection. Besides, the sublobectomy mentioned in their studies not only included wedge resection, but also other surgical methods such as segmental resection. To our knowledge, although wedge resection and segmentectomy were classified as sublobectomy, there were significant differences between them. Wedge resection was defined as non-anatomical resection of the lung parenchyma, and was not necessary to determine the histological structure of bronchus and pulmonary vessels. While segmentectomy was the anatomical resection of the lung parenchyma, and required the disconnection of segmental bronchus, segmental vessels and segmental parenchyma. In view of the different anatomical pathways of wedge resection and segmentectomy, it was necessary to discuss the two surgical methods separately. Different from the general sublobectomy in previous studies, the sublobectomy in this study was limited to wedge resection. This study further confirmed that stage IA SP-NSCLC patients with previous lung cancer-directed surgery demonstrated similar OS with lobectomy and wedge resection.
In clinical practice, the relative location of two primary tumors had an extremely important influence on the final selection of surgical procedure. Generally speaking, when two tumor lesions were in the ipsilateral different lobes, lobectomy for the second lesion tended to lead to pneumonectomy, which was a risk factor affecting the prognosis of patients [4, 14, 18]. This study found that when the two lesions were in the ipsilateral different lobes, wedge resection demonstrated equivalent OS to lobectomy. Thus, we believe that in this case, lobectomy for the second lesion may not result in a greater survival benefit than wedge resection. In agreement with our research, Ishigaki T and his colleagues  suggested that if FPLC and SPLC were on the same side of the lung and FPLC received lobectomy, sublobectomy should be a priority for the SPLC. Additionally, surgical choice regarding the optimal extent of resection for a second primary tumor on the contralateral side, is also controversial. Yang et al.  reported that a limited resection (sublobectomy) for the contralateral second tumor did not have a negative effect on OS in these patients with stage I bilateral MPLC. This was also confirmed by the findings of this study. Similarly, other previous studies [1, 14, 17, 18] did not demonstrate a significant difference in prognosis with respect to lobectomy versus sublobectomy for the second tumor. The choice of surgery for the second primary tumor is challenging for thoracic surgeons, especially for patients with history of lobectomy or pneumonectomy. In addition to the maximum preservation of pulmonary functional reserve, maximum tumor resection is also an oncological principle to be followed. An adequate margin (>2 cm or the tumor diameter) is a prerequisite for sublobectomy. In a number of studies [17, 21], sublobectomy has been proved to have similar therapeutic effect to lobectomy for patients with early single primary lung cancer. Therefore, we believe that under strict patient screening criteria, sublobectomy including wedge resection is worthy of choice for thoracic surgeons.
Overall, this study provided evidence that wedge resection produced similar survival rate to lobectomy in stage IA SP-NSCLC patients with previous lung cancer-directed surgery, and wedge resection and lobectomy had similar lung cancer specific mortality in most cases. A correct understanding of the difference in OS and lung cancer specific mortality between the two surgical approaches might help clinicians make more reasonable choices.
This study still has the following limitations. First, much of the detailed information (such as imaging findings, pulmonary function index, related basic diseases, etc.), which may be an important reference for clinicians to make treatment decisions, is not available in the SEER database. Second, the number of patients with stage IA SP-NSCLC included in this study was still relatively small, and the postoperative follow-up time was also short. Third, the nature of a retrospective study, and the strict screening criteria in this study inevitably resulted in selection bias. Considering the deficiency of retrospective analysis, further prospective analysis is recommended.
In conclusion, wedge resection demonstrated equivalent survival to lobectomy in Stage IA second primary NSCLC patients with lung cancer-directed surgery. Considering the limitations of the present study, relevant prospective studies are still necessary.