A flow diagram outlining the literature search process is presented in Fig. 1. A total of 1,477 potential studies were identified, including 570 from PubMed, 839 from EMBAS, 64 from the Cochrane Library, and 4 relevant studies yielded from the reference list. One thousand and forty-nine studies remained after duplicate publications were removed. After screening of the titles and abstracts of remained studies, nine hundred and forty-three studies were excluded, and the full texts of 106 studies were reviewed. Finally, forty-three studies with 7,118 patients were included in this meta-analysis [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66].

PRISMA flow diagram of literature retrieval. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses

The baseline characteristics and methodological assessment of included studies are presented in Table 1. All 43 studies were retrospective cohort studies conducted in 12 countries around the world. The publication dates of the included studies ranged from 2015 to 2023, and the sample sizes of the included studies ranged from 25 to 564. Eight studies reported the survival outcome of BRCA [24, 26, 27, 51, 54,55,56, 60], seven studies reported the survival outcome of ESCA [25, 28, 30, 32, 59, 61, 64], five studies reported the survival outcome of HNSC [29, 43, 46, 50, 57], and three studies reported the survival outcome of OV [31, 37, 62]. Two studies each explored the survival outcome of patients with BLCA [36, 63], COAD [39, 49], LIHC [34, 42], THCA [44, 53], STAD [45, 47], and SKCM [38, 40]. Only one study each reported the survival outcome of non-small cell lung cancer (NSCLC) [35], CESC [66], KIRC [33], SARC [41], READ [48], COADREAD [58], PAAD [52], and UCEC [65]. Thirty-two of the included studies reported the correlation between LAG3 expression and OS [24,25,26,27,28,29,30,31,32,33,34,35, 37, 38, 40, 42, 44,45,46,47, 50, 51, 54,55,56,57,58,59, 62,63,64, 66], fourteen reported the correlation LAG3 expression and DFS [24,25,26, 33, 34, 39, 42, 43, 45, 46, 48, 49, 52, 60], ten reported the correlation between LAG3 expression and PFS [37, 38, 41,