Molecular analysis of GCT shows that a single somatic missense mutation in the forkhead transcription factor FOXL2, c.402C > G (p.Cys134Trp) is present in 70%–97% of adults with GCT and has value as a diagnostic marker for this tumour type.21, 22, 23, 24, 25, 26. This evidence concerns the gene FOXL2 and granular cell tumor.