Does parosteal liposarcoma differ from other atypical lipomatous tumors/well-differentiated liposarcomas? A molecular cytogenetic study using combined multicolor COBRA-FISH karyotyping and array-based comparative genomic hybridization

Parosteal osteosarcoma associated with a low-grade component mimicking well-differentiated liposarcoma: a case report

Parosteal osteosarcomas and well-differentiated liposarcomas are both well-differentiated locally aggressive tumors. They both have simple karyotypes with amplification of the 12q13-15 regions including MDM2 and CDK4 genes. In this report, we describe the case of a parosteal osteosarcoma intertwined with a low-grade component similar to a well-differentiated liposarcoma. The association of a bone component with an adipose component was initially overlooked. We describe the histological, imaging, and molecular characteristics of this tumor stressing the importance of radio-pathological correlation. To our knowledge, this is the second report of a parosteal osteoliposarcoma. Awareness of this rare presentation may allow radiologists and surgeons to recognize the peripheral fatty component as an integral part of the tumor.

Fusion events lead to truncation of FOS in epithelioid hemangioma of bone

Epithelioid hemangioma of bone is a locally aggressive vascular neoplasm. It can be challenging to diagnose because of the wide histological spectrum, which can make it difficult to differentiate from other vascular neoplasms such as epithelioid hemangioendothelioma or epithelioid angiosarcoma. COBRA-FISH karyotyping identified a balanced t(3;14) translocation. Transcriptome sequencing of the index case and two other epithelioid hemangiomas revealed a recurrent translocation breakpoint involving the FOS gene, which was fused to different partners in all three cases. The break was observed in exon 4 of the FOS gene and the fusion event led to the introduction of a stop codon. In all instances, the truncation of the FOS gene would result in the loss of the transactivation domain (TAD). Using FISH probes we found a break in the FOS gene in two additional cases, in none of these cases a recurrent fusion partner could be identified. In total, FOS was split in 5/7 evaluable samples. We did not observe point mutations leading to early stop codons in any of the 10 cases where RNA was available. Detection of FOS rearrangement may be a useful diagnostic tool to assist in the often difficult differential diagnosis of vascular tumors of bone. Our data suggest that the translocation causes truncation of the FOS protein, with loss of the TAD, which is thereby a novel mechanism involved in tumorigenesis.