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:Theoretical studies (17) suggested that slowly growing immunogenic tumors that are sensitive to the immune response would engage regulatory T cell and induce tolerance to themselves, while poorly immunogenic, fast growing tumors would progress in a regulatory T cell independent manner.
Category: