Based on the whole exome sequencing results, we expanded our study to perform a focused genetic screen for mutations and/or LOH of the cell cycle regulators CDKN2A/B, RB1 and TP53 using a combination of a clinically validated next generation sequencing panel, MLPA, and FISH in a cohort of 71 GIST patients from well-defined clinical risk groups with annotated clinical follow up. Here, RB1 is linked to gastrointestinal stromal tumor.