Malignancy in Noonan syndrome and related disorders.

Noonan syndrome (NS) and related disorders, such as NS with multiple lentigines (formerly called LEOPARD syndrome), cardiofaciocutaneous syndrome, and Costello syndrome, constitute an important group of developmental malformation syndromes with variable clinical and molecular features. Their underlying pathophysiologic mechanism involves dysregulation of the Ras/mitogen-activated protein kinase signaling pathway, an essential mediator of developmental and growth processes in the prenatal and postnatal setting. Malignant tumor development is an important complication encountered in other RASopathies, such as neurofibromatosis type 1, but the neoplastic risks and incidence of malignant tumors are less clearly defined in NS and related disorders of the Noonan spectrum. Malignant tumor development remains an important complication variably seen in the RASopathies and, thus, a clear understanding of the underlying risks is essential for appropriate clinical care in this patient population. This review discusses previously published reports of malignancies in individuals with RASopathies of the Noonan spectrum.