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:Studies targeting the regulator of PI3K, PTEN—whose loss is common in medulloblastoma—have shown innate resistance to SHH inhibitors in PTEN null medulloblastomas compared to PTEN wild-type medulloblastoma [23].
Category: