1. Basic characteristics of manuscripts
A total of 1325 manuscripts in the area of PD-L1 in gastrointestinal cancers were retrieved. Among these manuscripts, there were 899 original articles (67.8%), 232 reviews (17.5%), 156 meeting abstracts (11.8%), 25 editorial materials (1.9%), 14 proceeding papers (1.1%), and 12 other documents (0.9%). One thousand three hundred thirteen manuscripts (99.1%) were written in English. Based on the calculator in WOS, each manuscript was cited 30.72 times. PD-L1 was also searched in different types of gastrointestinal cancers. The number of publications in gastric, esophageal, colon, pancreatic, hepatocellular, biliary, appendiceal, and small intestinal cancers were 345, 109, 560, 252, 278, 15, 0, and 0, respectively.
Institutions in 54 countries and areas participated in publication of these manuscripts. The United States (489), China (377), and Japan (172) published most of the manuscripts. The top 5 institutions publishing manuscripts were Harvard University (55), the University of Texas system (51), the VA Boston Healthcare System (50), Johns Hopkins University (42), and the Institut National de la Santé et de la Recherche Médicale (40).
Before 2010, only a few studies were published each year. In 2010, only 12 manuscripts were published. However, since 2011, the annual number of publications sharply increased (Figure 1). In 2018, 458 manuscripts were published. Additionally, manuscripts published in 2017 and 2018 accounted for almost half of the retrieved publications (44.2%, 586/1325). Moreover, the percentage of publications on PD-L1 focusing on gastrointestinal cancers increased over time. In 2010, gastrointestinal cancers accounted for only 5.8% (12/27) of all studies on PD-L1. However, in 2018, they accounted for 14.9% (458/3081) (Figure 2).
2. Overview of landmark manuscripts
The 1325 manuscripts about PD-L1 in gastrointestinal cancers also cited each other or some other literature in their references. Combined with their 31,960 references, a simplified co-citation network (Figure 3) of the manuscripts was constructed on the condition of the g-index as 5. In Figure 3, the 5 manuscripts according to the value of total citations were marked. They were summarized in Table 1 with the top 5 manuscripts according to the value of betweenness centrality and burstness.
Furthermore, since almost half (44.2%) of the manuscripts were published in 2017 and 2018, a co-citation network of all literatures during these 2 years was created. The top 5 manuscripts with the highest citation amount in the co-citation network are summarized in Table 2.
3. Key concepts in the research area
To identify key concepts about PD-L1 in gastrointestinal malignancies, a foam tree was constructed using the Carrot2 analytic software. The top 5 keywords with the highest frequency were circled with red line, as “gastric cancer,” “therapies for the treatment,” “colorectal cancer,” “PD-1 for the treatment,” and “CD8 T cells and tumor” (Figure 4).
Further, to detect novel concepts since 2014 (recent five years), a simplified co-citation network of author keywords (restricted with the condition of the top 50 phrases per year) was created (Figure5). In this map, three words with highest citation were “colorectal cancer”, “immunotherapy” and “pd-l1”.. Several such phrases with greater scientific importance are illustrated in Table 3, including three emerging between 2014 and 2015 (“Immunosuppression,” “IFN-gamma,” and “Regulatory t cell”), two emerging between 2015 and 2016 (“Ipilimumab” and “Mdsc”), one emerging between 2015 and 2018 (“Solid tumor”), and four emerging between 2016 and 2018 (“TIL,” “Her2,” “Radiation,” and “Atezolizumab”).
4. Topics in various gastrointestinal cancer types
To understand different subtopics in various gastrointestinal cancer types, a unique process termed “clustering” was utilized. Simplified co-citation networks (restriction on the condition of the g-index as 5) were constructed for colorectal, gastroesophageal, and hepatopancreatobiliary cancers, and studies in these three cancers were divided into 32, 23, and 25 clusters, respectively (Figure 6). The three largest clusters in each disease were summarized from the titles of manuscripts in the cluster (Table 4), which reflected the contents of each cluster. For example, in colorectal cancers, the terms summarizing the largest three clusters were “predictive biomarkers,” “advanced cancer,” and “prognostic significance.”