Atypical teratoid rhabdoid tumor pathophysiology
Pathology
AT/RT and rhabdoid tumor share the term "rhabdoid" because under a microscope both tumors resemble rhabdomyosarcoma.
Histology
The tumor histology is jumbled small and large cells. The tissue of this tumor contains many different types of cells including the rhabdoid cells, large spindled cell, epithelial and mesencymal cells and areas resembling primitive neuroectodermal tumor (PNET). As much as 70% of the tumor may be made up of PNET-likw cells. Ultrastructure characteristic whorls of intermediate filaments in the rhabdoid tumors (as with rhabdoid tumors 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
Immunohistochemistry refers to the process of localizing proteins in cells of a tissue section exploiting the principle of antibodies binding specifically to antigens in biological tissues. A tissue sample is stained to identify specific cellular proteins. 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. Below are proteins found in an Atypical Teratoid Rhaboid Tumor.
- 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
- S-100
- neurofilaments
- AFP- not found
- HCG – negative
Cytogenetic studies
Cytogenetics is the study of the tumor’s genetic make-up. A technique called fluoresecene in situ hybridization (FISH) has been gaining attention in the literature because it may be able to help locate a mutation or abnormality that may be allowing tumor growth. Also, 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. On the other hand, chromosomal 22 deletions are very comomon in AT/RTs.
In importance of the hSNF5/INI1 gene located on chromosomal band 22q11.2 is highlighted in the summary paper form the Workshop on Childhood Atypical Teratoid Rhabdoid Tumors as the mutation’s presence is sufficient to change the diagnosis from a medulloblastoma or PNET to the more aggressive AT/RT classification. However, it should be noted that 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.