Lung cancer has been a leading cause of cancer-related death worldwide for decades, with adenocarcinoma representing the most prevalent subtype (Sung H et al.2021). In recent years, with the popularity of low-dose spiral CT screening, more and more SMPLC are being diagnosed. At the same time, research on the diagnosis and treatment of multiple primary lung cancers has increased significantly. It is difficult to distinguish multiple primary lung cancers from intrapulmonary metastases, but the treatment options and prognosis of multiple primary lung cancers are completely different compared with intrapulmonary metastases, so the evaluation of diagnosis, treatment, and prognosis of multiple primary lung cancers is particularly important. Unlike previous studies, in this study, we retrospectively examined the clinical characteristics, surgical treatment, and long-term prognosis of all patients with postoperative lesions diagnosed as multiple primary lung adenocarcinoma by EGFR testing. We found a high heterogeneity of EGFR driver genes between tumors in patients with multiple primary lung adenocarcinoma, suggesting the importance of EGFR testing in the diagnosis of such patients.
In the present study, we classified lesions by their radiology, pathology type, and diameter size of the lesions, and then compared EGFR mutations in lesions in different categories. We found that the mutation rate of mixed GGO is significantly higher than that of pure GGO and solid nodules (SN); the mutation rate of invasive adenocarcinoma is significantly higher than that of other histology subtypes (AIS as well as MIA). These results are in general agreement with the findings of Liu et al (Liu M et al. 2018). The result also concurred with the hypothesis for the progression of lung adenocarcinoma that EGFR-mutated AAH follows a linear progression schema, whereby AAH progresses to AIS and is followed by MIA (Kobayashi Y et al. 2015; Yatabe Y et al. 2011). Sun and colleagues (Sun F et al. 2018) found that diameter size of GGO lesion correlated with EGFR mutation rates, with lesions ≥ 20 mm in diameter being more likely to be mutated than lesions < 20 mm in diameter, which is similar to the results of our study.
For multiple primary lung adenocarcinoma, we should routinely test for EGFR mutations in all lesions. Although multiple lung cancers with predominantly multiple GGO lesions or containing GGO lesions should be considered more often as multiple primary lung cancers, one study found the presence of similar somatic mutations by exon sequencing in multiple GGO lesions in two patients with multiple lung adenocarcinomas, including two pure GGO lesions in one patient (Li R et al. 2018). This suggests that intrapulmonary metastases can occur in patients with multiple GGO lesions. In the current study, all but three patients had solid lesions, and the rest contained at least one GGO lesion, yet postoperative pathology showed lymph node metastases in seven patients, all of whom should be considered to have multiple intrapulmonary metastases according to previous Martini-Melamed criterion (Martini N et al. 1975). Ye and colleagues (Ye C et al. 2016) reported a case of a patient with multiple primary lung adenocarcinoma in whom two tumors, one with EGFR mutation and one with KRAS mutation, were identified by genetic testing, and the lesion with the KRAS mutation was resected and followed by gefitinib-targeted therapy, after which the remaining lesion disappeared. Therefore, we believe that EGFR mutation can be a good supplement to histological, imaging and morphological evidence of tumor, so as to better distinguish multiple primary lesions from metastatic lesions and provide patients with a more accurate staging. In this study, analysis of EGFR testing results for all lesions revealed the presence of EGFR mutations in 108 lesions (67.1%), including 35.4% and 20.5% for L858R and 19DEL, respectively. This may be related to the fact that the patients in this study were non-smokers (77.1%) and the majority of female patients (68.6%).
Surgery remains the most effective treatment option for multiple primary lung cancers, but the specific surgical method is still controversial. Several studies (Ishikawa Y et al. 2014; Nakata M et al. 2004; Zhang Y et al. 2018; Chen TF et al. 2019) have shown that for multiple primary lung adenocarcinoma, lobectomy should be performed as far as possible for the primary lesion, while sublobar resection (segmental or wedge resection) can be performed flexibly for the secondary lesion, especially for patients with multiple bilateral lung lesions, which ensures adequate distance between the tumor margins and maximizes preservation of more lung function. Nakata and colleagues reported [24] that 26 patients with SMPLA, only 5 patients underwent lobectomy alone, and the 3-year OS and DFS were 92.9% and 77.9%, respectively. Ishikawa and colleagues also found (Ishikawa Y et al. 2014) that 93 patients with SMPLA, sublobar resection was used during surgery in 58% of patients, and the 3-year OS and RFS were 93.6% and 87% respectively. In the current study, since most of lesions were distributed in different lobes, we tried to adopt a combined sublobar resection approach during surgery, and the OS and RFS at 3 years reached 94.4% and 86%, respectively, which was comparable to the results of the above study. Our specific surgical strategy was: (1) for lesions that were all in the same lobe, we performed direct lobectomy; (2) for lesions that are on the same side but not in the same lobe, we performed anatomical lobectomy or segmentectomy for the dominant lesion ≥ 2 cm, and sublobar resection for the remaining lesions as much as possible; (3) In patients with multiple lesions in both lungs, we give preference to the side with less lung tissue removed to start the procedure, but if the left side is the dominant lesion and lobectomy is required, the surgery should start on the right side. (4) For all peripheral lesions, intraoperative rapid pathology should be performed as much as possible, and the extent of resection should be determined based on the rapid pathology results and imaging of the lesion, but sublobar resection should be performed as much as possible. (5) For GGO lesions, try to adopt sublobar resection as much as possible. In conclusion, we should take into account the characteristics of the tumor, the patient's physical condition, and the decisions of the physician to try to develop the best individualized treatment plan for each patient.
There are several limitations to our study. First, it is a retrospective study and selection bias cannot be avoided. Second, it is a single-center study with a small sample size, which needs to be further confirmed by multicenter study with larger sample size. Third, we did not test other tumor’s driver genes, such as KRAS, ALK, ROS1, and BRAF. A whole genome sequencing would be more accurate to identify the source of multiple tumors. Fourth, the postoperative follow-up time span is not long enough to appropriately assess long-term survival.
In conclusion, A high discordance of EGFR mutations were identified between tumors in patients with SMPLA, so the detection of EGFR mutation may be used routinely to prevents unnecessary adjuvant treatment for patients with histologically similar synchronous primary lung cancers. Synchronous multiple lung adenocarcinomas with predominantly multiple GGO should be considered as SMPLA, and surgery may be aggressively performed for these patients due to a good prognosis.