RB1 and neoplasm: Known genetic abnormalities that lead to tumor progression and worsening prognosis include homozygous deletion of CDKN2A and/or CDKN2B, amplification of CDK4, homozygous deletion or mutation of RB1, amplification of PDGFRA, alterations of MET, amplifications of MYCN, and mutations of PIK3R1 and PIK3CA [23].