Malignant
rhabdoid tumor and
epithelioid sarcoma are classified as
tumors of uncertain differentiation. However, it is controversial whether these
tumors are distinct entities because they share similar histological and immunohistochemical features such as the existence of rhabdoid cells or complete loss of
SMARCB1 protein expression.
MicroRNAs are small non-coding RNAs, and it is suggested that knowledge of
microRNA expression profiles in
cancer may have substantial value for diagnostics. We first analyzed
microRNA expression profiles in 13 frozen materials (five malignant
rhabdoid tumors, two proximal type
epithelioid sarcomas, and six conventional type
epithelioid sarcomas) and subsequently examined the specific
microRNA expressions in 29
paraffin-embedded materials (8 malignant
rhabdoid tumors, 13 proximal type
epithelioid sarcomas, and 8 conventional type
epithelioid sarcomas) and 13 previously described frozen materials by quantitative RT-PCR. According to the unsupervised hierarchical clustering of
microRNA, proximal type
epithelioid sarcoma and conventional type
epithelioid sarcoma were classified into the same category, whereas malignant
rhabdoid tumor was a distinct category from both types of
epithelioid sarcoma. In addition, when malignant
rhabdoid tumor with SMARCB1 gene alterations and proximal type and conventional type
epithelioid sarcoma with no SMARCB1 gene alterations were compared, 56
microRNAs were isolated as being significantly different (ANOVA, P<0.05). Among them, quantitative RT-PCR using frozen and
paraffin-embedded materials demonstrated that expression levels of miR193a-5p (P=0.002), which has been suggested to downregulate SMARCB1
mRNA expression, showed statistically different expression levels between malignant
rhabdoid tumor and
epithelioid sarcoma with no SMARCB1 gene alterations. These results suggest that
epithelioid sarcoma, especially proximal type
epithelioid sarcoma, and malignant
rhabdoid tumor are distinct
tumors with respect to the
microRNA expression profiles and that miR193a-5p may have an important role in the inhibition of SMARCB1
mRNA expression.