Task: Named Entity Recognition
Input (English):  The purpose of this study was to evaluate the in vitro activity of the principal metabolites of ATRA [ 4 - hydroxy - retinoic acid ( 4 - OH - RA ) , 18 - hydroxy - retinoic acid ( 18 - OH - RA ) , 4 - oxo - retinoic acid ( 4 - oxo - RA ) , and 5 , 6 - epoxy - retinoic acid ( 5 , 6 - epoxy - RA ) ] in NB4 , a human promyelocytic leukemia cell line that exhibits the APL diagnostic t ( 15 ; 17 ) chromosomal translocation and expresses the PML - RAR alpha fusion protein .
Output (English): fusion protein