Stage IV includes: Any pT, Any N, cM1 or pM1, Any H. cM1: Distant metastasis without microscopic confirmation. pM1: Distant metastasis with microscopic confirmation. HX: Unknown or insufficient evidence of a constitutional RB1 gene mutation. H0: Normal RB1 alleles in blood tested with demonstrated high-sensitivity assays. H1: Bilateral retinoblastoma, retinoblastoma with an intracranial primitive neuroectodermal tumor (i.e., trilateral retinoblastoma), patient with family history of retinoblastoma, or molecular definition of a constitutional RB1 gene mutation. (AJCC 8th ed.) [from NCI]