Primary clear cell sarcoma of the femur: a unique case with RT-PCR and direct sequencing confirmation of EWSR1/ATF1 fusion gene

Abstract

Background It is very rare for clear cell sarcomas (CCS) to arise in the bone. During diagnosis, it is important to distinguish primary CCS of bone from bone metastasis of melanoma because this difference fundamentally changes the therapeutic options. Recently, characteristic fusion genes of CCS have been detected using reverse transcription polymerase chain reaction (RT-PCR) or direct sequencing which allowed to distinguish CCS from melanoma. However, there was no study applying these analyses with positive results. In this case, we describe the use of fusion gene analysis to diagnose a primary CCS of the bone. Case presentation A 36-year-old male presented with a four-months history of left knee pain. Magnetic resonance imaging showed a lesion in the left femoral medial epicondyle. Histological examination of the biopsy specimen revealed proliferating oval or rounded cells. These cells had clear cytoplasm arranged in fascicles or compact nests with frequent deposits of brown pigment. Furthermore, immunohistochemistry analysis revealed that tumor cells were positive for S-100 protein, HMB-45, Melan-A, and SOX10. It stained negative for CD34 and BRAF v600e. Conclusively, detection of the EWSR1/ATF1 fusion gene using RT-PCR and direct sequencing confirmed that the lesion was a primary CCS of the bone. Wide-margin resection and reconstruction with a tumor endoprosthesis were performed. Conclusions Herein, we diagnosed a rare case of primary CCS of the bone by detecting EWSR1/ATF1 fusion gene using RT-PCR and direct sequencing. Since fluorescence-in situ hybridization (FISH) and RT-PCR could show false positive by mainly due to technical problems, it is better to perform direct sequencing to confidently diagnose the tumor as a primary CCS especially at very rare site such as bone.

Primary Clear Cell Sarcoma of Bone

“…Ten of 14 cases identified upon literature review either demonstrated negative FISH for EWSR1 rearrangement (4 cases) 26,27,30,31 or the testing was not performed or reported (6 cases). 22,24,29,[32][33][34] In 4 cases (Table 2), 21,23,25,28 the pathognomonic rearrangement was demonstrated either by FISH (2 cases), RT-PCR (1 case), or by an undescribed method (1 case). One of these tumors was negative for HMB-45 and melan A (a rare occurrence for CCS) 25 ; without confirmation of the fusion partner, it is difficult to be entirely certain that the diagnosis was correct.…”

“…While characteristic clinicopathologic characteristics of CCS (young patient age, predilection for tendons and aponeuroses of distal extremities, and uniform cytomorphology) can help suggest the diagnosis, rare presentations are particularly problematic and can easily lead to misdiagnosis as metastatic melanoma. One such circumstance is represented by primary bone presentation of CCS, previously reported as rare cases 21–34. Here, we report a series of primary bone CCS.…”

“…One such circumstance is represented by primary bone presentation of CCS, previously reported as rare cases. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Here, we report a series of primary bone CCS.…”

Patellar dislocation following distal femoral replacement after extra-articular knee resection for bone sarcoma: A case report

“…Magnetic resonance imaging (MRI) showed a bone tumor. An open biopsy was performed, and reverse transcription-polymerase chain reaction (RT-PCR) and direct sequencing revealed the EWSR1 / ATF1 fusion gene in the tumor specimens[ 14 ]. No other signs of metastasis were found on whole-body CT and positron emission tomography/CT.…”