LOH at the RB1 locus has been found in 25–45% of glioblastomas and in about 25% of anaplastic astrocytomas (AA), as well as in bladder carcinomas, and malignant neuroendocrine lung carcinomas (Ishikawa et al, 1991; Hogg et al, 1993; Xu et al, 1993; Gouyer et al, 1994; Henson et al, 1994; Ichimura et al, 1996). Here, RB1 is linked to anaplastic astrocytoma.