RB1 and neoplasm: Moreover, several studies in MPNST showed the inactivation of other additional tumor suppressor genes such as RB1 (Retinoblastoma 1), TP53 (Tumor protein p53), and PTEN (Phosphatase and Tensin homolog) in both NF1-associated and sporadic MPNSTs, highlighting a driving role of mutations in these genes in tumor malignancy [23].