Discussion on the repeated inclusion of randomized controlled trials in meta-analysis

I read an article written by Zhang et al. (1) out of interest recently, who performed a meta-analysis aimed to study the efficacy of hematopoietic stem cell transplantation (HSCT) combined with killer cells in the treatment of leukemia. The meta-analysis concluded that HSCT combined with killer cells effectively reduced the incidence of graft-versus-host disease (GvHD) in patients, while it had no significant effect on overall survival and recurrence rates. I do agree the most ideas in the paper and appreciate the results of the authors’ work. However, after a careful learning of the paper, I would like to raise a following suggestion.

As I known, repeatedly published studies which contained substantial overlapping data from the same patient population should be excluded in a meta-analysis (2). I have read and noticed that 2 studies in table 1, referred to Refs. 1 and 4, were with a same registration number (3,4). It indicated that there is a high probability that the two papers have duplicate research participants. Therefore, I suspectted that the authors should verifiy the repeated studies and exclude one of them.

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References

1. Zhang Y, Song Y, Ni Q, et al. Systematic review and meta-analysis: transplanted hematopoietic stem cells and killer cells on leukemia. Ann Palliat Med 2021;10:7872-83. [Crossref] [PubMed]
2. Kllén B. Drugs During Pregnancy. Cham: Springer, 2016:99-103.
3. Wang Y, Liu QF, Xu LP, et al. Haploidentical vs identical-sibling transplant for AML in remission: a multicenter, prospective study. Blood 2015;125:3956-62. [Crossref] [PubMed]
4. Chang YJ, Wang Y, Liu YR, et al. Haploidentical allograft is superior to matched sibling donor allograft in eradicating pre-transplantation minimal residual disease of AML patients as determined by multiparameter flow cytometry: a retrospective and prospective analysis. J Hematol Oncol 2017;10:134. [Crossref] [PubMed]