Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:As for SDH-related PPGL, FH-related paragangliomas present a pattern of global histone and DNA hypermethylation evocating that fumarate acts, like succinate, as an oncometabolite (Castro-Vega et al., 2014; Letouze et al., 2013; Morin et al., 2014).
Category: