RT Journal Article SR Electronic T1 Retinoic acid induced chordomas as a model of differential therapy JF Saudi Medical Journal JO Saudi Med J FD Prince Sultan Military Medical City SP 1236 OP 1237 VO 30 IS 9 A1 Omer F. Bayrak A1 Esra Aydemir A1 Fikrettin Sahin YR 2009 UL http://smj.org.sa/content/30/9/1236.abstract AB