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:The well-known tumor suppressor p53 is a transcriptional master regulator that regulates the expression of genes associated with a wide range of functions, including cell-cycle arrest, apoptosis, and senescence in response to genotoxic andnongenotoxic stresses that challenge cellular genomic integrity (1).
Category: