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:Nevertheless, such discrepancies between the levels measured in the primary tumor and metastases and CTCs have been described before at both the mRNA and the protein level(37, 42, 48-51), indicating that the findings with our multi-gene measuring technique may indeed be relevant.
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