Low-grade fibromyxoid sarcoma (LGFMS) is a distinctive fibroblastic neoplasm that is characterized by alternating collagenous and myxoid areas, deceptively bland spindle cell morphology, a whorling architecture, and a t(7;16) translocation involving FUS and CREB3L2.
Distinct chromosomal translocations have been identified in several myxoid sarcomas, including t(12;16)(q13;p11) FUS-DDIT3 in myxoid liposarcoma, t(7;16)(q34;p11) FUS-CREB3L2 in low-grade fibromyxoid sarcoma, and t(9;22)(q31;q12) EWSR1-NR4A3 in extraskeletal myxoid chondrosarcoma.
FUS-CREB3L2 was capable of activating transcription from CD24 regulatory sequences in luciferase assays, suggesting an important role for the upregulation of this gene in LGFMS.
However, supernumerary ring chromosomes have been identified in a subset of FUS/CREB3L2-positive LGFMS, but it has not yet been formally demonstrated that such ring chromosomes harbor the FUS/CREB3L2 fusion gene.
Recently, a link has been suggested between SEF and low-grade fibromyxoid sarcoma (LGFMS) on the basis of the finding of the characteristic translocation t(7;16) (FUS-CREB3L2) of LGFMS in a small number of studied cases of SEF.
Reported herein is a case of primary pulmonary HSCT that had FUS-CREB3L2 fusion transcripts, a product of characteristic chromosomal abnormality t(7;16)(q33;p11) of HSCT and LGFMS.
Results showed 50% of cases tested positive for the FUS-CREB3L2 translocation by RT-PCR and 81.8% by FISH, suggesting FISH is more sensitive than RT-PCR for confirming LGFMS diagnosis.
Reverse transcriptase-polymerase chain reaction analysis disclosed a FUS/CREB3L2 fusion transcript in 22 of the 23 (96%) cases that remained classified as LGFMS after the histologic re-evaluation and from which RNA of sufficient quality could be extracted, whereas none of the cases that were classified as other tumor types was fusion-positive.
The results indicated that FUS/CREB3L2 is specifically associated with LGFMS and that RT-PCR or FISH analysis may be useful for the differential diagnosis.
This fusion has recently been described as a variant translocation in low-grade fibromyxoid sarcoma (LGFMS), a tumor more typically characterized by a recurrent t(7;16) chromosomal translocation, resulting in the fusion of FUS and CREB3L2 genes.
We here show that a t(7;16)(q33;p11) in two cases of low grade fibromyxoid sarcoma fuses the FUS gene to BBF2H7, a previously uncharacterized gene that is homologous to the Drosophila Bbf-2 gene.
We present a case of an ossifying tumor of the perineum that required an open biopsy and fluorescent in situ hybridization testing for FUS and CREB3L2 for diagnosis as a variant of low-grade fibromyxoid sarcoma.
While the majority of LGFMS cases are characterized by a FUS-CREB3L1 fusion, both FUS-CREB3L2 and EWSR1-CREB3L1 fusions were recently demonstrated in a small number of LGFMS and SEF/LGFMS hybrid tumors.