A rare case of clear cell sarcoma with 4 types of EWSR1-ATF1 fusions detected not in primary site but in metastatic site

Clear cell sarcoma is a unique tumor which has EWSR1-ATF1 or EWSR1-CREB1 fusion. Several patterns of EWSR1-ATF1 fusion are observed in clear cell sarcoma. Since type 5–7 fusions were reported recently, they are classified as type 1–7. We examined EWSR1-ATF1 and EWSR1-CREB1 fusions in a single case of clear cell sarcoma with lung metastasis in a 36-year-old Japanese man. As a result, we found only type 1 EWSR1-ATF1 fusion in the primary site, but 4 types of EWS-ATF1 fusion (type 1, 2, 5, 6) were detected in the metastatic site. These 4 types of fusion were completely identical to the recent report, but the case had the same fusion patterns in both primary and metastatic sites. In our case, increased splicing activity in the EWSR1-ATF1 fusion might be acquired at the metastatic site. There is another possibility that metastasis might develop through the increased splicing activity in the fusion.