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 patients with late stages of tumorigenesis, TGFB1 may favor a more aggressive phenotype by promoting tumor growth and resistance to apoptosis or by enhancing tumor cell motility and eventually the outgrowth of distant metastases [17].
Category: