tokens: In preliminary screens , mutations of PTEN were detected in 31 % ( 13 / 42 ) of glioblastoma cell lines and xenografts , 100 % ( 4 / 4 ) of prostate cancer cell lines , 6 % ( 4 / 65 ) of breast cancer cell lines and xenografts , and 17 % ( 3 / 18 ) of primary glioblastomas .