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:Both pro-apoptotic (e.g., Han et al., 2001; Leskov et al., 2003; Caccamo et al., 2005) and antiapoptotic (e.g., Trougakos and Gonos, 2004; Gleave and Chi, 2005) functions have been ascribed to CLU which is up-regulated in several tissues including testis, following injury or stress.
Category: