is known in which two half-brothers were diagnosed with CNS atypical teratoid/rhabdoid tumors (AT/RT). The two boys, diagnosed at 2 months and 17 months of age, had a germline insertion mutation in exon 4 of the INI1 gene that was inherited from their healthy mother. A maternal uncle died in childhood from a brain tumor and a malignant rhabdoid tumor of the kidney. The identification of two unaffected carriers in a family segregating a germline mutation and rhabdoid tumor supports the hypothesis that variable risks of development of rhabdoid tumor in the context of a germline mutation may exist. Most rhabdoid tumors may occur in a developmental window. This family highlights the importance of mutation analysis in all patients with a suspected rhabdoid tumor. In the first case report of monozygotic twins, both with brain tumors having similar genetic alterations, authors suggest a common genetic pathway. A case was reported of an infant who developed both AT/RT and renal rhabdoid tumors that were identical in gross and immunologic histology. A family has had multiple generations of posterior fossa tumors including rhabdoid tumors and choroid plexus carcinoma. A germline mutation (SMARCB1) was found in both affected and some unaffected family members. Two sisters were diagnosed with AT/RTs 15 days apart. A case report stated no karyotypic anomalies were noted. Three siblings had a mutation of the SMARCB1 gene and one had a choroid plexus carcinoma and two had an AT/RT. Although the mother had a normal somatic DNA, the mutation apparently was inherited from the mother's germline due to a mutation during oogenesis. Izycka-Swieszewska et al. describe a five-month-old child with an AT/RT, whose father was diagnosed with a primitive neuroectodermal tumor (PNET) of the spinal canal. Fluorescent in situ hybridization analysis showed significant genetic differences in the specimens which suggest that the occurrence of these virulent CNS malignancies within a single family was coincidental. Pathology AT/RT and rhabdoid tumor share the term "rhabdoid" because under a microscope, both tumors resemble rhabdomyosarcoma. Histology The tumor histopathology is jumbled small and large cells. The tissue of this tumor contains many different types of cells including the rhabdoid cells, large spindled cells, epithelial and mesenchymal cells, and areas resembling primitive neuroectodermal tumor (PNET). As much as 70% of the tumor may be made up of PNET-like cells. Ultrastructure characteristic whorls of intermediate filaments are seen in the rhabdoid tumors (as with rhabdoid tumors