Please cite G. Yu (2015) for using ReactomePA. In addition, please cite
G. Yu (2012) when using compareCluster in clusterProfiler package, G.
Yu (2015) when applying enrichment analysis to NGS data by using
ChIPseeker

  Guangchuang Yu, Qing-Yu He. ReactomePA: an R/Bioconductor package for
  reactome pathway analysis and visualization. Molecular BioSystems
  2016, 12(2):477-479

A BibTeX entry for LaTeX users is

  @Article{,
    title = {ReactomePA: an R/Bioconductor package for reactome pathway analysis and visualization},
    author = {Guangchuang Yu and Qing-Yu He},
    journal = {Molecular BioSystems},
    year = {2016},
    volume = {12},
    number = {12},
    pages = {477-479},
    pmid = {26661513},
    url = {http://pubs.rsc.org/en/Content/ArticleLanding/2015/MB/C5MB00663E},
    doi = {10.1039/C5MB00663E},
  }