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:Treatment options include surgical excision, chemotherapy, immunotherapy with rituximab for patients with positive CD 20 immunohistochemistry, or radiosurgery.(1-30) For patients without systemic involvement, external beam radiotherapy (EBRT) is often used after histopathologic confirmation.
Category: