In the database search, a total of 852 records were obtained. After removal of 302 duplicates, 550 studies were screened on the basis of their titles and abstracts. Out of these, 477 studies were excluded because of ineligible patients, treatments, and study designs. The remaining 73 studies underwent full-text examination. In cases where full-text format was not available, abstracts were further assessed for eligibility. Among these assessments, 49 studies were excluded. Ultimately, a total of 23 studies published in English were deemed eligible and included in the analysis (Fig. 1) [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41].

PRISMA flowchart. PRISMA preferred reporting items for systematic review and meta-analyses, RAM ramucirumab

The 23 included studies published between 2016 and 2021, 4 (17.4%) from South Korea [20, 25, 34, 41] and 19 (82.6%) from Japan [18, 19, 21,22,23,24, 26,27,28,29,30,31,32,33, 35,36,37,38,39,40]. Of the 23 studies, 8 (34.8%) were controlled studies [21, 23, 24, 26, 30,31,32, 34, 38], and 15 (65.2%) were non-controlled studies. With one prospective study [25], all studies (95.7%) were retrospective. Additionally, 6 studies (26.1%) were conducted in multiple centers [18, 20, 21, 30, 32, 34], 12 (52.2%) were conducted in a single center [19, 22,23,24, 26,27,28,29, 31, 33, 35,36,37], and the location of the remaining 5 (21.7%) was unknown [25, 38,39,40,41]. Of these included studies, 11 (47.8%) were available in full text [18,19,20,21,22,23,24,25,26,27, 34, 35], and the other 12 (52.2%) were presented as conference abstracts (Table 1).

The sample size of included studies ranged from 8 to 3650, with 43.5% of studies having more than 100 patients [18, 20,21,22,23,24,25,26, 30, 32, 34]. The median age ranged from 57 to 75 years [19,20,21, 24,25,26,27, 30, 31, 34, 35], and male individuals accounted for more than half of the patients [18,19,20,21, 24,25,26,27, 30, 34, 35]. Eight (34.8%) studies reported the location of tumor metastases, including peritoneum, liver, lung, lymph nodes, bone, and others [18, 20,21,22,23,24, 26, 35, 40]. First-line treatments were described in 16 (69.6%) studies [18,19,20,21,22,