Pediatric histiocytic sarcoma (HS) clonally related to anteceding leukemia is a rare malignancy with poor outcome. We performed a molecular characterization of HS and the corresponding leukemia by methylation arrays and whole-exome sequencing and found a variety of aberrations in both entities with deletions of CDKN2A/B as a recurrent finding. Furthermore, data from genome-wide mutation analysis from one patient allowed the reconstruction of a sequence of tumorigenesis of leukemia and HS lesions including the acquisition of a putatively activating KRAS frameshift deletion (p.A66fs). Our results provide an insight into the genetic landscape of pediatric HS clonally related to anteceding leukemia.
