As indicators of clonality we selected three molecular markers that are affected at high frequency in either predominantly astrocytic tumors, i.e. TP53- mutation, or in predominantly oligodendroglial tumors [11], [12], i.e. LOH1p/19q, or show similar frequencies in both, i.e. IDH1- mutations affecting codon 132. The gene discussed is IDH1; the disease is oligodendroglial tumor.