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:Assessment for ALT in mouse GBM Previous characterization of human GBM has shown an association between mutations of ATRX and the maintenance of telomere length by ALT, or nontelomerase-based, pathways (1, 8).
Category: