Global trends of researches on pycho-oncology during 1999-2019: A 21-year bibliometric study based on VOSviewer


 BackgroundThe studies on psycho-oncology are growing rapidly, but there were no bibliometric studies regarding psycho-oncology. This study was to explore a bibliometric analysis of psycho-oncology in the past 21 years at a global level.MethodsThe literature was searched in Web of Science (WOS) by using subject terms. VOSviewer software was used for bibliometric analysis of the retrieval results.ResultsThe literature search yielded 1921 papers. After screening process, 968 papers were included, which came from 55 countries/regions, 1,452 organizations and 4,152 authors. The top three countries/regions, organizations and authors ranked by the number of published papers were the United States of America (USA) (286), Germany (143) and Australia (130); the Memorial Sloan-Kettering Cancer Centre (MSKCC) (New York, USA) (34), Newcastle University (Newcastle, Australia) (29) and McGill University (Montreal, Canada) (28); Luigi Grassi (University of Ferrara in Italy) (26), Tatsuo Akechi (Nagoya City University Hospital in Japan) (20) and Anja Mehnert (University of Leipzig in Germany) (18), respectively. Moreover, the 968 papers contained 1,768 author keywords, involved in 300 journals and cited 28,311 references. The top three co-occurrence author keywords, most-involved journals and most-cited references were “Quality-of-life”, “Depression” and “Breast cancer”; Psycho-Oncology, Supportive Care in Cancer and Journal of Psychosocial Oncology; “Zigmond AS, 1983”, “Zabora J, 2001” and “Mitchell AJ, 2011”, respectively.ConclusionsThere was a growing trend in published papers related to psycho-oncology, with the organizations and authors from developed countries leading the field. “Quality-of-life”, “Depression” and “Breast cancer” reflected the most hotspots, and the latest progress can be tracked in Psycho-Oncology.

influence of psychosocial factors on the occurrence, treatment and prognosis of various diseases, especially cancers, has been paid more and more attention around the world [1,2]. In these several decades, psycho-social oncology, also called psycho-oncology, has been an interdisciplinary discipline and developed as a specialized branch of clinical psychology [3]. Psycho-oncology studies the psychological, emotional and spiritual reactions caused by cancers, the psychosocial care of cancer patients and their families, as well as the role of psychological and behavioral factors in the occurrence, development and prognosis of cancers [4]. With the increasing incidence of cancers, the prevention and treatment of cancers has become an important public health problem. Meanwhile, psycho-oncology has become an essential component of the multi-disciplinary treatment (MDT) for cancers [5,6].
Mapping knowledge domains (MKD) came into being at the beginning of the 21st century and has been widely used in business, education, health care and other fields these years [7]. MKD rising in the field of scientometrics and knowledge metrology is a visual graphic mode of analyzing knowledge structures, exploring research hotspots and deeply mining knowledge information [8]. There have been more than thirty kinds of tools for MKD, such as VOSviewer, CitNetExplorer, Citespace, HisCite, CRExplorerhe and RPYS i/o and so on [9][10][11][12]. Most of the tools are easy to operate and have powerful features. Among them, VOSviewer, developed by Leiden University Science and Technology Research Center in the Netherlands, has a unique advantage to map and visualize the network of countries/regions, organizations, authors, keywords that are related to psycho-oncology [13].
In 2014, Hack TF et al. conducted a historical review of psycho-oncology and supportive care research in Canada using citation analysis [14]. Citation analysis is useful for examining the research performance of psycho-oncology and supportive care researchers and identifying leaders among them. However, citation analysis is less intuitive than MKD to demonstrate the course and current situation of psycho-oncology. Thus, the purpose of this study was to conduct a worldwide development trend research on pycho-oncology during 1999-2019 based on VOSviewer. The present study will be helpful for researchers to select relevant hotspots and to find suitable teams to collaborate with and research platforms to use.

Methods
Data sources, search strategies and data extraction The core collection database of Web of Science (WOS) was used to search for literature on psychooncology in a single day February 22, 2020 by two authors (CJZ, GFH) independently. All data were downloaded form public database and had nothing to do with human subjects. Thus, ethical approval was not required. The theme index was presented as follow: "psycho oncology" OR "psychosocial oncology" OR "oncology, psychosocial" OR psychooncology OR psycho-oncology, and the time span was set from 1999 to 2019. The search results were subsequently filtered to include peer-reviewed articles and reviews in English. Detailed process of the enrollment and screening was shown in Fig. 1.
The original .txt data were downloaded from the WOS, including title, publication year, journal information, countries/regions, organizations, authors, author keywords, abstract and cited references, and so on. Two independent authors (CJZ, GFH) conducted the data extraction simultaneously to ensure that the search data were accurate and comprehensive.

Bibliometric Analysis
The bibliometric analysis in this study was performed and visualized using VOSviewer 1.6.14 (Leiden University, Leiden, Netherlands) by two authors (CJZ, XCQ) independently. VOSviewer 1.6.14 can be downloaded and used freely from https://www.vosviewer.com/download.
We analyzed the cooperation situation in the field of psycho-oncology among countries/regions, organizations and authors via co-authorship analysis; the author keywords in the field of psychooncology via co-occurrence analysis; the publication of journals via bibliographic coupling analysis; and the cited references via co-citation analysis. Additionally, the global publications distribution was analyzed by bibliographic coupling analysis of countries/regions, and the visualization result was selected "Overlay Visualization".

Results
Overview of publications on psycho-oncology A total of 1921 papers were detected through a comprehensive literature search. After the screen strategies, a total of 968 published papers met the inclusion criteria for this study. On the whole, there was a growing trend both in publications and citation in the past 21 years (Fig. 2A).

Co-authorship Analysis Of Countries/regions
In this study, the VOSviewer 1.6.14 software was used to analyze the network visualization of coauthorship relationships between 55 different countries/regions. Only countries/regions with a minimum of five articles were included. A total of 32 countries/regions were identified, however, among which Singapore was not connected to each others. Thus, the remaining 31 countries/regions were divided into seven clusters, as shown in Fig. 3A. Furthermore, the co-authorship analysis

Co-authorship Analysis Of Authors
Analysis using the VOSviewer 1.6.14 software revealed that the 968 articles totally included 4,152 authors, in which the same one author's name may had several different ways of writing. Only authors with a minimum of five articles were included in co-authorship analysis. A total of 54 authors were identified, which were divided into 12 clusters, as shown in Fig. 3E. Some of the 54 authors in the network map were not connected to each other, while the network map also showed massive collaborations between authors, such as Luigi Grassi and Rosangela Caruso both from University of

Co-occurrence Analysis Of Author Keywords
A total of 1,768 author keywords in the 968 papers on psycho-oncology were extracted by the VOSviewer 1.6.14 software. As shown in Fig. 4A, 37 author keywords defined as terms that cooccurred the minimum number of 10 time within title and abstracts in all papers were analyzed using a co-occurrence network analysis tool in the VOSviewer 1.6.14 software. In this analysis, these 37 author keywords were classified into 4 large clusters. In addition, the distribution of these 37 author keywords according to the average time they appeared in the articles showed that "Fear of cancer recurrence" may indicate the main research hotspots in recent years ( Supplementary Fig.S3).
Furthermore, the co-occurrence analysis of 1,768 author keywords was shown in Supplementary   Fig.S4.
The top 10 author keywords ranked by the number of co-occurrence were shown in Fig. 4B. The most commonly used keywords were "Quality of life"(131), "Depression"(90) and "Breast cancer"(68), respectively. Furthermore, the author keywords with the three highest total link strength were "Quality of life"(139), "Depression"(127) and "Anxiety"(95),respectively.

Bibliographic Coupling Analysis Of Journals
A total of 300 journals had published articles in field of psycho-oncology. Using the VOSviewer 1.6.14 software, 33 journals published 5 or more papers were included in the bibliographic coupling analysis of journals, as shown in Fig. 4C. These 33 journals were classified into 5 large clusters.

Co-citation Analysis Of Cited References
By the VOSviewer 1.6.14 software, the analysis revealed that the 968 articles totally cited 28,311 references. Forty-four references with a citation frequency greater than 20 were selected to create the co-citation map, as shown in Fig. 4E. All of them were classified into four clusters. These cited which were about Hospital Anxiety and Depression Scale (HADS) [18]. The HADS was a self-rated screening questionnaire detecting mild degrees of anxiety and depression. Although it was designed for general medical hospital outpatients, it had been widely used in primary care. Citation frequency of the second most-cited article was 95 time, which was contributed by Zabora James from the Johns Hopkins University School of Medicine (Baltimore, USA). This article entitled "The prevalence of psychological distress by cancer site" was published on Psycho-Oncology in 2001 [19]. The third most-cited article (72 times) was written by Alex J Mitchell from Leicester Partnership Trust (Leicester, UK), which was a meta-analysis study aimed to quantitatively summarise the prevalence of depression, anxiety, and adjustments disorders in oncological, haematological and palliative-care settings [20]. Besides, the aforementioned three papers also ranked respectively the top three for the total link strength.

Discussion
The development of psycho-oncology between the East and the West Our study showed that the top 10 countries/regions, organizations and authors ranked by the number of publications were totally from developed countries, which inevitably dominated the psycho-oncology field of research. Given the fact that the definition of psycho-oncology was initially proposed by Jimmie Holland at MSKCC (New York, USA) in 1970s, developed countries have fostered integration and implementation of psycho-social care much earlier than developing countries [21][22][23]. On the other hand, the condition of basic medical research, clinical trials and academic advantage appear to be superior in developed countries, which may play an important role in this phenomenon.
However, over last two decades, gained lots of experience, guidance and strengthened support from the scholars of developed countries, low-and middle-income countries in Asia, Africa, Latin America, such as Mainland China, India, Nigeria, Kenya, South Africa, Brazil and so on have developed their own working groups or societies in the field of psycho-oncology [24][25][26]. In 2006 Jimmie Holland was invited to Mainland China to join in the preparation work of building Chinese Psychosocial Oncology Society (CPOS) and give academic lecture to Chinese colleagues [23,27]. Moreover, in 2016 CPOS published the first Chinese Psychosocial Oncology Therapy Guidelines for Cancer patients in China, which represented a milestone in the development of Chinese psycho-oncology clinical practice [28].
Notably, nowadays the International Psycho-Oncology Society (IPOS), which represents over 9000 psycho-oncology professionals in more than 90 countries around the world, is committed to fostering the science of psychosocial and behavioral oncology and improving the quality of life for those affected by cancer globally [29].
The hotspots and emerging field of psycho-oncology It is clear that psychosocial oncology researchers includes individuals with diverse clinical and research backgrounds, including physicians, psychologists, psychiatrists, rehabilitation specialists, physiotherapists, genetic counselors, nurses, social workers, epidemiologists, social scientists and educators. Thus, the research themes of psychosocial oncology correspondingly cover a broad rang.
Of note, our analysis of the 48 research directions suggested that the biomedical social sciences and health care sciences services had received enough attention or study over the last two decades. From the social and public health perspective, it can extensively and unambiguously advocate toward the adoption of Standard of Quality in Cancer Care and Clinical Practice Guidelines [17,30,31]. Moreover, our co-occurrence analysis of author keywords identified that "Quality of life", "Depression" and "Breast cancer" were the three most hotspots in psycho-oncology research. Breast cancer is the most common malignancy among women with a relative long-term survival; addressing survivors' unique post-treatment needs is critical to providing quality cancer care, which partially explain why we come to this conclusion in this analysis [32,33].
Additionally, we should pay some attention to the emerging field or innovative ideas of psychooncology research, such as psychosocial issues in genetic testing and internet-based psychosocial interventions. In fact, "Genetic testing"(1 time), "Genetic mutation"(1 time), "Genetic counseling"(1 time), "Genetic panel testing"(1 time), "Telephone"(9 times), "online"(7 times), "Telehealth/ehealth/mhealth"(5 times) and "Internet-based/IT-based"(4 times) have emerged in titles of the 968 articles. For instance, a study investigated the psychosocial consequences of genetic counseling and testing for hereditary breast and ovarian cancer. The results suggested that the psychological needs of undecided counselees warranted ongoing attention and potential follow-ups [34]. Anther recent article entitled "Development and usability evaluation of an online selfmanagement intervention for fear of cancer recurrence (iConquerFear)" indicated that iConquerFear had the potential to address the unmet supportive care needs reported by burgeoning numbers of cancer survivors [35]. In particular, during the outbreak period of 2019 New Coronavirus (2019-nCoV) pneumonia, psychological crisis intervention has been initiated via remote (telephone and internet) and onsite medical services to help medical workers, patients, and others affected to overcome any psychological difficulties [36]. Thus, online psychological therapy programs may have the feasible, tailored and interactive advantage in psychological interventions, and further research is necessary to explore ways to optimize the use of this approach.

Study limitations
Although our data analysis was relatively comprehensive and objective, this study had some shortcomings. First, the literature was only searched in WOS core collection database. There are indeed other database for bibliometric analysis, such as Pubmed and Scopus. However, to the best of our knowledge, Thomson Reuters' WOS is the most appropriate database for performing bibliometric analysis [37]. Second, some important studies related to research area of psycho-oncology in non-English language were not included and analyzed. Third, there were differences between the bibliometric analysis results and the real research situations, since some latest published high-quality studies were not focused on because of their low citation frequency [37]. Therefore, it may be necessary to update the bibliometric analysis in the future. In fact, every database or method has its merits and weaknesses. In our opinion, bibliometric analysis is just a useful method to comprehend rapidly the performance statistics, research hotspots, latest frontiers and trends in some field but not "complete picture".

Clinical implications
As we all know, the predominant purpose of psycho-oncology is to guide cancer patients, their families or caregivers to cultivate positive coping styles and ultimately improve quality of life, emotional function, and social function in patients with cancer [4,38]. In our study, an overview of the global research on psycho-oncology was presented, which provided a better understanding of the global trends in the research on psycho-oncology and indicated the directions for further studies.
Thus, the clinical implications of our study were indirectly but profound. Additionally, this study indicated that there was not enough randomized controlled trial (RCT) research on psycho-oncology, and high-quality evidence was limited. It is indeed essential for potential future developments, which also urges for further clinical applications of psycho-oncology.

Conclusion
Our study detailed the performance statistics, research hotspots, latest frontiers and trends in psycho-oncology field. The developed countries made the most outstanding contribution within this important field, as well as assisting the developing countries with experience and guidance. "Qualityof-life", "Depression" and "Breast cancer" were the most common related area and should be closely followed. Authors interested in this field should pay more attention to Psycho-Oncology. The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. All bibliometric analysis could be replicate again.
Ethics approval and consent to participate All data were downloaded form public database and had nothing to do with human subjects. Thus, ethical approval was not required. The need for consent was waived by our medical ethics committee of Shanghai Mental Health Center. It was deemed unnecessary according to our medical ethics committee and national regulations.

Consent for publication
Not applicable.

Competing interests
The authors declare that they have no competing interests.