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. 2019 Apr 15;19:353. doi: 10.1186/s12885-019-5569-5

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© The Author(s). 2019

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 1 — PRISMA Chart. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Note: Some studies were reported in multiple publications; in such cases, the main study report was classed as the “primary” publication, and any other articles reporting on the same trial were classed as “secondary reports.” Therefore, the primary reports are all unique trials