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:Serum CA125 is presently considered as a marker of response to treatment rather than a screening/diagnostic marker (Van der Berg et al, 1988; Tuxen et al, 1995; Rustin et al, 1996; Zanotti and Kennedy, 1999).
Category: