Global research trends on the links between the gut microbiome and cancer: a visualization analysis

For source publication retrieval, the Scopus database was chosen as the target database. Scopus is widely recognized as one of the best online databases for bibliometric research [34, 35].

We used the Scopus online database’s “Advanced search” feature and inserted the appropriate keywords to find relevant literature on microbiota and cancer from the last 2 decades (from January 2001 to December 31, 2020). To prevent bias caused by ongoing database updates, document extraction and export should be done within 1 day (March 19, 2021). Synonyms for the gut microbiota and cancer were used as in the following search strategy.

An Excel spreadsheet was used to collect the following data as bibliometric indicators: total number of publications, year of publication, publication types, to ten funding agencies, top ten countries, top ten institutions, top ten journals, most cancer types related to microbiota based in the top keyword, and top ten citations.

The VOSviewer software tool (version 1.6.16) was used to build, visualize and explore networks of countries, authors, and terms, with links between items based on their cooccurrences [36, 37], was applied to create network visualization maps of the most cooccurrence terms to determine the hotspots for frontier studies, as well as the most coauthorships of countries.

In total, 2061 publications were included in this study. Articles made up 1346 of the total number of publications, accounting for 65.31% of the total number of records, making them the most popular form of literature. There were 511 reviews, representing 24.79 percent of the total. The other eight types of publications were 204 documents, representing 9.90% of the total, including letters, book chapter, notes, book, editorials, minutes of meetings, erratum, and short surveys.

During the past 2 decades, the number of microbiota and cancer publications increased yearly, from 10 in 2001 to 486 in 2020, as shown in Fig. 1. The growth of the publication showed two stages: the first (2001–2016), which had a very slow rate of publication production, and the second (2017–2020), which had a much faster rate of publication progress.

At least 112 different countries participated in the publication of studies on the microbiota and cancer in the last 2 decades. A total of 1568 articles written in the top ten countries represented 70.8% of all studies in the related area (Table 1). The United States (n = 566) was the largest contributor, followed by China (n = 478), Italy (n = 135), Japan (n = 122) and the United Kingdom (n = 94). In addition, the United States and China had the largest number of publications involving international scholars. Figure 2 shows a network mapping chart of international research collaborations on microbiota and cancer from 2001 to 2020 among the leading participating countries. The total number of authors published on microbiota and cancer was 9102, of which 25 published more than 15 documents.

The Institut National de la Santé et de la Recherche Médicale (INSERM) in France had the highest number of publications among institutions worldwide, with 40 publications, which accounted for 1.94% of all publications. The National Cancer Institute of the USA was the second prolific institute with 35 (1.70%) publications, followed by the MD Anderson Cancer Center of the University of Texas in the USA with 30 (1.46%) publications, the Ministry of Education of China with 28 (1.36%) and the University of North Carolina at Chapel Hill in the USA with 28 (1.36%) publications (Table 2).

Of the documents that were retrieved, USA funding agencies were the most active in this field, the National Natural Science Foundation of China (n = 211; 10.24%) being the most active, followed by the National Cancer Institute (n = 186; 9.02%), National Institutes of Health (n = 163; 7.91%) and the National Institute of Diabetes and Digestive and Kidney Diseases (n = 80; 3.88%) (Table 3).

The top 10 journals with the most publications related to microbiota and cancer are listed in Table 4. Scientific Reports had the highest number of publications among journals worldwide, with 40 publications representing 1.94% of all publications. The International Journal of Molecular Sciences and PloS ONE were the second with 33 (1.6%) publications for each journal, followed by Frontiers in Microbiology with 27(1.31%) publications.

Table 5 summarizes the top ten most cited papers in the microbiota and cancer during the last 2 decades based on total citations. The top 10 highest citations ranged from 1378 to 441 [38‐47]. Routy et al. [44], published in Science in 2018, had the highest overall citation frequency (number of citations = 1378) among the top ten publications with total citation frequency.

Terms with a minimum number of occurrences greater than 50 in all included publications were analyzed using VOSviewer. There are 109 terms that reach this threshold out of 34,784 in this field, which were divided into three clusters and colored differently. The three clusters are “microbiota composition and gene expression” (cluster 1, green), “effect of probiotics on cancer” (cluster 2, red), and “host-microbiome interaction in cancer immunotherapy” (cluster 3, blue); (Fig. 3). In cluster 1, the most striking keywords are sequence, abundance, composition, healthy control, and patient. In cluster 2, the most common keywords are effect, probiotic, ability, apoptosis, proliferation, reduction, cancer cell, and inhibition. In cluster 3, the keywords with the most repetition are microbiome, evidence, pathogenesis, cancer, immunotherapy, interaction, cancer therapy, and immunity. These results demonstrated that the most prominent fields of microbiota and cancer included 3 directions during the past 20 years. Keywords were color coded by VOSviewer based on the average time they appeared in the 2061 related publications (Fig. 4). The terms in blue appeared earlier, and those in yellow and green appeared later. Before 2016, most studies focused on the ‘effect of probiotics on cancer’. The latest trends showed that ‘microbiota composition and gene expression’ and ‘host-microbiome interaction in cancer immunotherapy’ would be more concerned more widely in the future.

Table 6 lists the most frequent keywords related to cancer types occurrences in microbiota literature from 2001 to 2020. The top keywords indicate that colorectal cancer is strongly related to microbiota in the literature, followed by breast cancer, stomach cancer, and lung cancer (Table 6).

The current study is the first bibliometric study of its kind to look at this emerging topic and provide comprehensive information on research trends and hotspots in this field. Three elements of current research are unique: (1) the use of Scopus, the largest database available; (2) the use of terms related to the gut microbiota and cancer comprehensively; and (3) it is global in scope. Finally, the findings of our research have some limitations. First, this study’s analysis is based on papers found in the Scopus database. Although this database contains most of the majority of research papers on gut microbiota and cancer, other databases such as PubMed and WoS may have some publications related to our topic, which is a weakness of this article. Second, the fact that we only included publications on cancer or gut microbiota in the article title has an inherent flaw; our experience has shown that including search items in the abstract has a much lower sensitivity and would have only found a small number of additional papers, if any. If we include terms from the abstract in our search query without any restrictions, we will get a lot of irrelevant publications that are not related to our subject. Despite these limitations, we believe that the findings provide a reliable representation of the performance of the gut microbiota and cancer research at a global level.