Sentence: Differences were observed when palbociclib or ribociclib was used in combination with letrozole or anastrozole or fulvestrant .
Drug combination annotation:
[{'class': 'COMB', 'spans': ['palbociclib', 'letrozole'], 'is_context_needed': True}, {'class': 'COMB', 'spans': [0, 3], 'is_context_needed': True}, {'class': 'COMB', 'spans': [0, 4], 'is_context_needed': True}]