The Value of Chest CT in Staging of Gastric Cancer

Aims: Gastric cancer (GC) is one of the most common malignant tumors in the world. However, the signicance of chest computed tomography (CT) in staging of GC is uncertain and the relevant study is few. So this study aims to evaluate the value of chest CT in gastric cancer staging. Methods: This study included 1158 cases of GC patients admitted to Shaoxing People's Hospital from 2015 to 2018. Chest, abdominal and pelvic CT scans were used to systematically evaluate the site of metastasis. All images were reviewed twice by two radiologists. Clinical data was Statistically analyzed. Results: The study nally included 846 patients, 672 cases (79.4%) received surgical treatment. Only 55 cases (6.5%) had lung metastases before or after surgery, and 20 cases (2.4%) had thoracic or supraclavicular lymph nodes (LN) metastases, of which 8 cases had double lung and thoracic LN metastases. The most common site of metastases is the peritoneum (265/390, 67.9%). Almost all lung or thoracic LN metastases accompanied with metastases to other sites, only one patient had a single thoracic LN metastases (1/846, 0.12%), while no single lung metastases was found. When tumor involved gastric fundus/cardia, compared to distal GC, there was a higher probability of lung metastases, and the difference was statistically signicant (P=0.028). Conclusions: This study 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.

In the staging treatment of colorectal cancer, it is often reported that the proportion of lung metastases is low and the clinical signi cance is uncertain. Therefore, chest CT is not recommended routinely in some literatures [11] . However, for the same digestive tract tumor, there are relatively few studies on the clinical signi cance of chest CT in GC, and the signi cance of chest CT in staging and treatment of GC is uncertain. In a retrospective study of 808 patients with GC, Chong [12] et al. found that the value of chest CT was limited due to the rarity of isolated lung metastases (0.4%) in patients with gastric cancer. While Chen AH [13] et al. conducted a study on 1669 patients with GC and found that only 5.6% of the patients with tumor recurrence included lung metastases, and all of the patients had multi-site metastases. Therefore, it is not recommended to routinely use chest CT for staging GC.
So this study aims to evaluate the value of chest CT in gastric cancer staging.

Patient Data
In this study, 1158 cases of GC patients admitted to Shaoxing People's Hospital from 2015 to 2018 were retrospectively studied. Among them, 312 cases were excluded due to incomplete chest and abdominal CT or clinicopathological data or incomplete follow-up data, and the remaining patients were followed up for at least 2 years. In this study, chest, abdominal and pelvic CT scans were used to systematically evaluate the site of metastases at initial diagnosis and at postoperative follow-up. TNM staging was performed using the seventh (2010) versions of the AJCC/IUCC staging system.

Image evaluation
The chest was evaluated by 16-slice plain CT, and the slice thickness was 2.5mm. The abdominal and pelvis were evaluated by 64-slice enhanced CT, the slice thickness was also 2.5mm. And 5 min before abdominal CT evaluation, the patient was instructed to drink 1000ml of water for contrast imaging. All images were reviewed twice by two radiologists with more than 5 years of working experience. If the CT was performed by another hospital, it was also reviewed by at least two radiologists and the image quality was quali ed.

Statistical analysis
The clinical characteristics, pathological stages and follow-up data of all patients were provided by the clinical database, and patients with incomplete data needed to be excluded. The chi-square test was used for classi cation variables. Data analysis was performed using SPSS 19.0.

Results
This study included a total of 1158 patients with pathological diagnosis of GC, who treated in Shaoxing People's Hospital from 2015 to 2018, in which 56 cases with incomplete image information, 18 cases with incomplete clinical pathological information, and 238 cases with incomplete 2 years follow-up information was ruled out. The study nally included 846 patients, male 533 cases (63.0%), female 313 cases (37.0%), average age 69 (36-97). Among them, 672 cases (79.4%) received surgical treatment, 420 cases (62.5%) were males and 252 cases (37.5%) were females. While the remaining 174 cases(20.6%) of the phase tumors, 113 cases (64.9%) were male. The speci c clinical data are shown in Tables 1 and  2.    Table 4). Interestingly, when we combined the cases of primary lung metastases and postoperative lung metastases to further increase the sample size, we were pleasantly surprised to nd that when tumor involved gastric fundus/cardia, there was a higher probability of lung metastases, and the difference was statistically signi cant (P = 0.028, Table 5).

Discussion
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 in uence 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 signi cant, which was considered to be related to the small sample size. When we conducted an uni ed test for all metastatic cases, we found that, compared with distal GC, the incidence of lung metastases was signi cantly increased when the tumor involved gastric fundus/cardia, and the difference was statistically signi cant. 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 insu cient, and the data of some cases is lost. We also hope that quali ed 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 de ciencies, 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.