Rhabdoid tumor is characterized by rhabdoid cells and shows complete loss of SMARCB1/INI1
protein expression. In existing classifications, the diagnostic synonyms vary depending on the anatomic site:
rhabdoid tumors in the central nervous system or extra-central nervous system are, respectively, classified as atypical
teratoid/rhabdoid tumor or malignant
rhabdoid tumor. In this study, we analyzed the histological, immunohistochemical,
microRNA, and clinicopathological statuses of
tumors initially diagnosed as malignant
rhabdoid tumor (n=33), atypical
teratoid/rhabdoid tumor (n=11), and pediatric undifferentiated/unclassified
sarcoma (n=8) with complete loss of SMARCB1/INI1 expression, and considered the possibility of their histological reclassification. Our analysis indicated that the
tumors could be histologically reclassified into three groups: conventional-type
tumors resembling malignant
rhabdoid tumor, atypical teratoid/rhabdoid-type
tumors resembling atypical
teratoid/rhabdoid tumor, and small cell-type
tumors resembling
malignant lymphoma. The reclassified conventional type was composed of 27 malignant
rhabdoid tumors and 9 atypical teratoid/
rhabdoid tumors (36 cases). The atypical teratoid/rhabdoid type consisted of six malignant
rhabdoid tumors, two atypical teratoid/
rhabdoid tumors, and two undifferentiated/unclassified
sarcomas (10 cases). The six cases of small cell type were made up of six undifferentiated/unclassified
sarcomas. All of the available
tumor specimens were positive for
vimentin and epithelial marker (EMA,
CAM5.2, or AE1/AE3).
MicroRNA profiles were not significantly different between the conventional- and small cell-type
tumors (Pearson's correlation coefficient: 0.888300 or 0.891388). There was no significant difference in overall survival between atypical
teratoid/rhabdoid tumor and malignant
rhabdoid tumor (P=0.16). In addition, there were no significant differences in survival between any of the reclassified combinations. In conclusion, we could classify eight
tumors initially diagnosed as undifferentiated/unclassified
sarcomas into two cases of atypical teratoid/rhabdoid type and six cases of small cell type. We suggest that reclassification of malignant
rhabdoid tumors into three groups according to their histologic features rather than the traditional classification by sites of origin would be favorable for their histopathological diagnosis.