in any area of the body). Ho and associates found sickle-shaped embracing cells, previously unreported, in all of 11 cases of AT/RT. Immunohistochemistry Immunohistochemical staining is widely used in the diagnosis and treatment of cancer. Specific molecular markers are characteristic of particular cancer types. Immunohistochemistry is also widely used in basic research to understand the distribution and localization of biomarkers in different parts of a tissue. Proteins found in an ATeratoid/RT are: Vimentin-positive Cytokeratin-positive Neuron specific enolase-positive Epitelial membrane antigen-positive Glial fibrillary acidic protein- positive Synaptophysin Chromogranin Smooth muscle actin Desmin Carcinoembrionary antigen CD99 antigen; S-100 neurofilaments AFP – not found HCG – negative Cytogenetic studies Cytogenetics is the study of a tumor's genetic make-up. Fluorescent in situ hybridization may be able to help locate a mutation or abnormality that may be allowing tumor growth. This technique has been shown to be useful in identifying some tumors and distinguishing two histologically similar tumors from each other (such as AT/RTs and PNETs). In particular, medulloblastmas/PNETs may possibly be differentiated cytogenetically from AT/RTs, as chromosomal deletions of 17p are relatively common with medulloblastoma and abnormalities of 22q11.2 are not seen. However, chromosomal 22 deletions are very common in AT/RTs. In importance of the hSNF5/INI1 gene located on chromosomal band 22q11.2 is highlighted, as the mutation's presence is sufficient to change the diagnosis from a medulloblastoma or PNET to the more aggressive AT/RT classification. However, this mutation is not present in 100% of cases. Therefore, if the mutation is not present in an otherwise classic AT/RT immunohistochemical and morphologic pattern then the diagnosis remains an AT/RT. Diagnosis The standard work-up for AT/RT includes: Magnetic resonance imaging (MRI) of the brain and spine Lumbar puncture to look for M1 disease Computed tomography (CT) of chest and abdomen to check for a tumor Bone marrow aspiration to check for bone tumors. Sometimes the physician will perform a stem cell transplant Bone marrow biopsy Bone scan The initial diagnosis of a tumor is made with a radiographic study (MRI or CT-). If CT was performed first, an MRI is usually performed as the images are often more detailed and may reveal previously undetected metastatic tumors in other locations of the brain. In addition, an MRI of the spine is usually performed. The AT/RT tumor often spreads to the spine. AT/RT is difficult to diagnose only from radiographic study; usually, a pathologist must perform a cytological or