With the fast development of CT imaging technology, more and more countries and regions using CT to clinical stage and prognosis of malignant tumor[14]. GC as a cancer of high incidence in China, even in the world, according to NCCN guidelines, chest, abdominal and pelvic CT can be used as the diagnostic basis for preoperative staging and postoperative recurrence[14, 15]. However, combined with our actual clinical experience and existing literature reports, the incidence of lung metastases in GC is relatively low[9, 10]. This study found that in the 846 included cases, only 55 cases (19 + 36, 6.5%) had lung metastases before or after surgery, and 20 cases (12 + 8, 2.4%) had thoracic or supraclavicular LN metastases, of which 8 cases had double lung and thoracic LN metastases, and more importantly, only one patient had a single thoracic LN metastases (1/846, 0.12%), while no single lung metastases was found. In addition, when lung or thoracic LN metastases occurs in GC cases, most of them are associated with intraperitoneal metastases. Therefore, when abdominal and pelvic CT indicates metastases, the clinical stage of the patients is all advanced, so whether lung metastases is present or not, it has no influence on the choice of treatment plan. So it is suggested that chest CT has limited value in the staging of GC, and frequent CT examination not only increases the economic burden of patients and medical insurance, but also increases the workload of radiologists, which will also cause more radiation damage to patients.
Although GC is one of the most common malignant tumors in the world, its incidence varies around the world. In East Asia, distal GC is more common, while in Western countries, although the overall incidence is low, the proportion of proximal GC is relatively high[1, 2]. In this study, it was found that compared with distal GC, when tumor involved gastric fundus/cardia, there would be a higher proportion of lung metastasis in primary advanced cases or postoperative recurrence cases, although the difference was not statistically significant, which was considered to be related to the small sample size. When we conducted an unified test for all metastatic cases, we found that, compared with distal GC, the incidence of lung metastases was significantly increased when the tumor involved gastric fundus/cardia, and the difference was statistically significant. It has been reported that lung metastases of GC is mainly realized through hematogenous dissemination[7, 16, 17]. When the tumor is in the distal of the stomach, the tumor cells can pass around the stomach arteriovenous access portal system or celiac trunk artery system, and then transferred to the liver, lungs or bones, while when the tumor is located in the fundus or cardia, tumor cells not only can transfer to the lungs by conventional path, also through the transport branches between the esophagus and stomach or the inferior phrenic artery. Compared with distal GC, the tumor metastasis pathways are more abundant and shorter, so the probability of lung metastases is higher.
Of course, this study has its limitations. First of all, due to the limitation of single-center study, the sample size is small, the follow-up period is insufficient, and the data of some cases is lost. We also hope that qualified units can carry out multi-center retrospective study, so as to further improve the reliability of the results on the basis of increasing the sample size. Secondly, according to the literature description, lung metastases in the chest CT images on the characteristics of the performance are often as random distribution, discrepancy size, uneven thickness of nodules[18], and although we study by two or more radiologists to double check, but failed to pathological diagnosis, there may be some error. Thirdly, compared with plain chest CT, enhanced CT can improve the detection rate of lung neoplasm. Despite these deficiencies, this study still shows that chest CT has a low application value in the routine staging of gastric cancer, but when the tumor is located in the fundus/cardia, due to the high proportion of lung metastases, chest CT has a certain existence value.