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 complexity of the tumor is increased by its extreme heterogeneity, supported by a vast array of genetic changes and cross-talk between signaling pathways (36, 37), which supply and sustain its high proliferation rate and its ability to infiltrate the surrounding normal parenchyma, representing themajor driving force behind tumor recurrence.
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