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:In chronic myeloid leukemia and multiple myeloma, SMOH is thought to be responsible for the maintenance of the cancer stem cell sub-population propagating the leukemia (Peacock et al., 2007; Dierks et al., 2008; Zhao et al., 2009).
Category: