Antigenicity of fusion proteins from sarcoma-associated chromosomal translocations

Synovial sarcoma (SS), clear cell sarcoma (CCS), and desmoplastic small round cell tumor (DSRCT) are soft-tissue malignancies occurring primarily in adolescents and young adults. These tumors contain specific chromosomal translocations that fuse the 5' region of one gene with the 3' region of another, resulting in the formation of characteristic fusion proteins. These translocations are unique to tumor cells and may be required for persistence, thereby serving as targets for immunotherapy. It was hypothesized that the fusion breakpoint sequences associated with SS, CCS, and DSRCT can serve as tumor-specific neoantigens. To test this, peptides corresponding to the fusion breakpoints were designed and assessed for ability to bind to various class I HLA molecules. Two peptides derived from the SS breakpoint specifically bind the HLA-B7 antigen, and a 10-amino acid minimal epitope was identified for this interaction. Specific binding of a SS peptide and a CCS peptide to HLA-B27 molecule was also observed. Finally, a peptide designed from the DSRCT breakpoint specifically binds the HLA-A3 molecule, and a 9-amino acid optimal epitope was identified for this interaction. The physiological/immunological relevance of these peptide/MHC interactions was demonstrated by the induction of SS-specific CTLs from normal donor lymphocytes using in vitro stimulation with autologous, peptide-pulsed dendritic cells and by the ability of these CTLs to lyse human SS tumor cells endogenously expressing the full-length fusion protein. These results suggest that sequences in the fusion region of sarcoma-associated chimeras can bind class I HLA molecules and serve as neoantigens. These may be useful for the development of novel immunotherapies for sarcoma patients with appropriate HLA molecules and tumors bearing these translocations.

Molecular features in a biphenotypic small cell sarcoma with neuroectodermal and muscle differentiation

We report a case of a 13-year-old girl with soft tissue sarcoma of the hand, which showed muscle and neuroectodermal immunophenotypes. Molecular studies were performed on RNA collected from fine-needle aspiration (FNA) cytology and peripheral blood samples by nested reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot analysis. This biphenotypic tumor showed simultaneous expression of EWS-FLI1 and PAX3-FKHR transcripts, specific of Ewing family tumors and alveolar rhabdomyosarcoma, respectively. Although childhood sarcomas with simultaneous muscle and neural differentiation have been described to have EWS-FLI1 transcripts, there are no reports of tumors with both transcripts. Cytological specimens are a good source of RNA for molecular studies.

Appraisal of the comparative utility of immunohistochemistry and electron microscopy in the diagnosis of childhood round cell tumors

To provide an objective assessment of the comparative utility of fluorescence- and peroxidase-based immunohistochemistry and electron microscopy, an observer blinded study was conducted under realistic study conditions utilizing a large sampling of poorly differentiated pediatric round cell tumors. Working independently, using a single ancillary technique of particular expertise, each of three investigators attempted to render a specific diagnosis with regard to 50 diagnostically challenging tumors. The results were compared against the subsequent "file diagnosis" established by consensus with all relevant information made available. A grading scheme was applied wherein points were awarded based on the accuracy and confidence of diagnosis. A comparative efficiency rating, expressed as a percentage, was formulated by dividing the number of points awarded each technique by the total number of points theoretically available. Electron microscopy proved superior overall, with an efficiency rating of 89%. Immunoperoxidase and immunofluorescence studies yielded efficiency ratings of 71 and 61%, respectively. Used in combination, the techniques achieved an efficiency rating of 95%. Application of these ancillary techniques resulted in a revision of the provisional diagnosis in 11 of 50 cases, and left only two cases without a firm specific diagnosis.

Soft tissue small round cell tumors: morphological parameters

Soft tissue small round cell tumors (SRCTs) comprise a heterogeneous group of neoplasms that predominate in childhood and adolescence and share similar morphological features, consisting of dense cellular proliferation of small round cells with a primitive appearance. Rhabdomyosarcomas, peripheral neuroepitheliomas, Ewing's sarcomas, and lymphomas/leukemias are the prototypic SRCT; other recently described tumors that should be added to the list are the desmoplastic SRCT and the rhabdoid tumor of soft tissues. In addition, several other primary soft tissue neoplasms and metastatic tumors have occasionally been considered in the differential diagnosis of SRCT. The precise identification of a given SRCT is important because of its clinical relevance. However, it may be difficult because the diagnostic criteria are sometimes subtle and several histologic and immunohistochemical features are not specific and/or may be simulated by different tumor types. We discuss the morphological clues that in our opinion are most useful for their diagnosis, the criteria for distinguishing between peripheral neuroepithelioma and Ewing's sarcoma, and the main diagnostic pitfalls.

Histology, immunohistochemistry, and electron microscopy of small round cell tumors of bone

Small round cell tumors (SRCTs) of the bone make up a family of primary bone sarcomas with morphologically, biologically, and clinically specific features. Among them, Ewing's sarcoma (ES) is the most common entity, but several varieties such as atypical ES, large cell ES, and ES with neuroectodermal differentiation (peripheral primitive neuroectodermal tumor of the bone or neuroepithelioma of the bone) have been identified recently. Histology and electron microscopy together with the variable expression of several epitopes (as shown by immunohistochemistry, mainly HBA/71 [Mic2 antigen]) provide the basis for characterizing the group within the context of neuroectodermal-derived neoplasms. A number of other ES-like tumors with small round cells, mimicking those previously described, have been characterized; Askin's tumor of the thoracopulmonary region will be considered as an ES similar to those already described, but within a particularly anatomic location. On the other hand, the presence of an endothelial appearance within a poorly differentiated neoplasm may be present in some ES-like SRCTs (atypical ES with endothelial features). The differential diagnosis with other sarcomas defined by small round to spindle cell contours might prove difficult. Particular attention must be paid to small cell osteosarcoma and mesenchymal chondrosarcoma. Likewise, "primitive sarcoma of bone" is considered in this study because it is a very rare neoplasm differing from the formerly discussed types; its pluripotentiality provides this tumor a blastemic character and a multiphenotypic expression. Malignant non-Hodgkin's lymphoma is an unusual presentation when primary to the bone, previous to any other anatomic location. Several subtypes have been considered within a histology that encompasses that seen in lymph nodes.

Desmoplastic small round cell tumor

Desmoplastic small round cell tumor is an undifferentiated tumor associated with serosal surfaces, especially the peritoneum. It is found predominantly in adolescents and young adults and is much more common in males than in females. The tumor has a characteristic histology, with extensive stromal tissue around islands of small and undifferentiated cells revealing the desmoplastic appearance. The coexpression of epithelial and mesenchymal antigens distinguishes this entity from other small round and blue cell tumors of this age group. Cytogenetic studies showed a t(11;22) translocation that differs from the Ewing's tumor translocation and seems to be specific to this entity. The involvement of the WT1 and EWS genes in the translocation makes this tumor an interesting subject for research on histogenesis and differentiation in small round and blue cell tumors.