Complex t(5;8) involving the CSPG2 and PTK2B genes in a case of dermatofibrosarcoma protuberans without the COL1A1-PDGFB fusion

Dermatofibrosarcoma protuberans (DFSP) is a rare, dermal neoplasm of intermediate malignancy. It is made of spindle-shaped tumor cells in a storiform pattern positive for CD34. Cytogenetically, DFSP cells are characterized by either supernumerary ring chromosomes composed of sequences derived from chromosomes 17 and 22 or more rarely of translocations t(17;22). These chromosomal rearrangements lead to the formation of a specific chimeric gene fusing COL1A1 to PDGFB. So far, the COL1A1-PDGFB fusion gene remains the sole fusion gene identified in DFSP. However, some observations suggest that genes, other than COL1A1 and PDGFB, might be involved in some DFSP cases. We report in this paper a DFSP case presenting as a unique chromosomal abnormality a complex translocation between chromosomes 5 and 8. This is the first report of a DFSP case where the lack of chromosomes 17 and 22 rearrangement and the absence of COL1A1-PDGFB fusion gene have been demonstrated. Using fluorescence in situ hybridization analysis, we showed that the CSPG2 gene at 5q14.3 and the PTK2B gene at 8p21.2 were disrupted by this rearrangement. Although rare, the existence of cases of DFSP negative for the COL1A1-PDGFB fusion has to be taken in consideration when performing molecular diagnosis for a tumor suspected to be a DFSP.     

Gains of COL1A1-PDGFB genomic copies occur in fibrosarcomatous transformation of dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans is a superficial low-grade sarcoma that rarely evolves into a high-grade fibrosarcoma. Dermatofibrosarcoma protuberans is genetically characterized by the unbalanced chromosomal t(17;22)(q21;q13), usually in the form of a supernumerary ring chromosome. The product of this chromosomal translocation is the chimeric gene COL1A1-PDGFB (collagen type I alpha I-platelet-derived growth factor beta), which is amplified at low levels in the ring chromosome. The aims of this study were to evaluate (1) whether genomic gains of this fusion gene occur during the clonal evolution of dermatofibrosarcoma protuberans into fibrosarcomatous dermatofibrosarcoma protuberans and (2) whether there is a difference between the number of genomic copies of COL1A1-PDGFB between classic dermatofibrosarcoma protuberans and dermatofibrosarcoma protuberans areas associated with fibrosarcomatous dermatofibrosarcoma protuberans. Eleven cases of fibrosarcomatous dermatofibrosarcoma protuberans with both dermatofibrosarcoma protuberans and fibrosarcomatous areas and 10 cases of classic dermatofibrosarcoma protuberans were studied. Genomic copies of COL1A1-PDGFB were evaluated by fluorescence in situ hybridization using a custom designed probe for the PDGFB locus on 4 mum thick paraffin-embedded tissue sections. Genomic gains of the COL1A1-PDGFB gene were observed in six (of 10) fibrosarcomatous dermatofibrosarcoma protuberans in the fibrosarcomatous areas when compared to the dermatofibrosarcoma protuberans areas of the same tumor (2-7 gene copies (median PDGFB copy gain, 2.8) versus 1-3 gene copies (median PDGFB copy gain, 1.7), respectively, P=0.004). Four fibrosarcomatous dermatofibrosarcoma protuberans did not show genomic gains of COL1A1-PDGFB fusion gene between the two areas. Essentially no difference in the copy number of COL1A1-PDGFB fusion gene was observed between dermatofibrosarcoma protuberans areas of classic dermatofibrosarcoma protuberans and dermatofibrosarcoma protuberans areas of fibrosarcomatous dermatofibrosarcoma protuberans (median PDGFB copy gain of 1.8 versus 1.7, respectively, P=0.36). Genomic gains of COL1A1-PDGFB fusion gene is possibly an oncogenic mechanism that is identified in the clonal evolution of a subset of dermatofibrosarcoma protuberans that evolves into fibrosarcomatous dermatofibrosarcoma protuberans. Since this finding was not observed in all cases of fibrosarcomatous dermatofibrosarcoma protuberans, other oncogenic mechanisms may be operating in this form of tumor progression. Copy number of COL1A1-PDGFB fusion gene in the classic dermatofibrosarcoma protuberans areas does not seem to be a major predisposing mechanism for fibrosarcomatous transformation.     

Fusion of COL1A1 exon 29 with PDGFB exon 2 in a der(22)t(17;22) in a pediatric giant cell fibroblastoma with a pigmented Bednar tumor component. Evidence for age-related chromosomal pattern in dermatofibrosarcoma protuberans and related tumors

In contrast with classic dermatofibrosarcoma protuberans (DP), genetic information about the juvenile or pigmented variant forms of DP, so-called giant cell fibroblastoma (GCF) and Bednar tumor (BT), is limited. In the sole karyotyped case of BT a supernumerary ring containing chromosomes 17 and 22 sequences, similar to DP rings, was reported, whereas in three GCF cases, t(17;22) or der(22)t(17;22) with COL1A1-PDGFB fusion involving exons 11, 40, and 47, respectively, have been described. Here, we report the first cytogenetic and molecular analysis of a tumor from a 5-year-old child that contained both GCF and BT components. The karyotype and molecular analyses confirmed the common histogenetic origin between DP, GCF, and BT in showing the presence of a der(22)t(17;22) fusing the COL1A1 exon 29 to PDGFB exon 2. Because COL1A1 exon 29 has been involved previously in gene fusion with PDGFB exon 2 in several cases of adult or infantile DP presenting either t(17;22) or ring chromosomes, our results support the concept that DP, GCF, and BT are morphologic variants of a same entity, rather than distinct tumors. Of interest, our findings give prominence to the relation between patient age and the chromosomal rearrangement pattern in DP and related tumors. Whereas only a few adult DP cases presented with translocations, all the infantile cases, either DP, GCF, or mixed BT-GCF, as shown here, contained translocation derivatives but not ring chromosomes. All the ring chromosomes were observed in adult cases. With respect to cytogenetic studies, DP, GCF, and BT appear to be a unique model for age-related chromosomal rearrangement progression.     

石蜡包埋隆突性皮肤纤维肉瘤组织中COL1A1/PDGFB融合基因的表达

目的检测隆突性皮肤纤维肉瘤(DFSP)中COL1A1／PDGFB融合基因的表达并探讨其临床病理学意义。方法应用一步法逆转录一聚合酶链反应(RT-PCR)检测12例4％甲醛固定、石蜡包埋DFSP组织中t(17;22)(q22;q13．1)染色体易位融合基因COL1A1／PDGFB mRNA表达,并选用2例纤维肉瘤、2例恶性纤维组织细胞瘤、3例平滑肌肉瘤、1例神经鞘瘤、1例纤维组织细胞瘤作为对照。结果12例DFSP中8例(67％)检出COL1A1／PDGFB mRNA的表达,其中PDGFB分别与COL1A1不同的位点相融合,而对照组均为阴性。结论用一步法RT-PCR检测石蜡包埋DFSF组织中特异性的COL1A1／PDGFB mRNA的表达,有助于DFSP的诊断和阐明其分子发生机制。     

Genetics of dermatofibrosarcoma protuberans family of tumors: from ring chromosomes to tyrosine kinase inhibitor treatment

Dermatofibrosarcoma protuberans (DP) is a rare, slow-growing, infiltrating dermal neoplasm of intermediate malignancy, made up of spindle-shaped tumor cells often positive for CD34. The preferred treatment is wide surgical excision with pathologically negative margins. At the cytogenetic level, DP cells are characterized by either supernumerary ring chromosomes, which have been shown by using fluorescence in situ hybridization techniques to be derived from chromosome 22 and to contain low-level amplified sequences from 17q22-qter and 22q10-q13.1, or t(17;22), that are most often unbalanced. Both the rings and linear der(22) contain a specific fusion of COL1A1 with PDGFB. Similar to other tumors, the COL1A1-PDGFB fusion is occasionally cryptic, associated with complex chromosomal rearrangements. Although rings have been mainly observed in adults, translocations have been reported in all pediatric cases. DP is therefore a unique example of a tumor in which (i) the same molecular event occurs either on rings or linear translocation derivatives, (ii) the chromosomal abnormalities display an age-related pattern, and (iii) the presence of the specific fusion gene is associated with the gain of chromosomal segments, probably taking advantage of gene dosage effects. In all DP cases that underwent molecular investigations, the breakpoint localization in PDGFB was found to be remarkably constant, placing exon 2 under the control of the COL1A1 promoter. In contrast, the COL1A1 breakpoint was found to be variably located within the exons of the alpha-helical coding region (exons 6-49). No preferential COL1A1 breakpoint and no correlation between the breakpoint location and the age of the patient or any clinical or histological particularity have been described. The COL1A1-PDGFB fusion is detectable by multiplex RT-PCR with a combination of forward primers designed from a variety of COL1A1 exons and one reverse primer from PDGFB exon 2. Recent studies have determined the molecular identity of "classical" DP, giant cell fibroblastoma, Bednar tumor, adult superficial fibrosarcoma, and the granular cell variant of DP. In approximately 8% of DP cases, the COL1A1-PDGFB fusion is not found, suggesting that genes other than COL1A1 or PDGFB might be involved in a subset of cases. It has been proposed that PDGFB acts as a mitogen in DP cells by autocrine stimulation of the PDGF receptor. It is encouraging that inhibitory effects of the PDGF receptor tyrosine kinase antagonist imatinib mesylate have been demonstrated in vivo; such targeted therapies might be warranted in the near future for treatment of the few DP cases not manageable by surgery.     

Molecular and clinicopathological analysis of dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a dermal and subcutaneous tumor of intermediate malignancy. The most remarkable cytogenetic feature of DFSP is the chromosomal translocation t(17;22)(q22;q13), causing a fusion of the platelet-derived growth factor beta chain (PDGFB) gene at 22q13, and the collagen type 1 alpha 1 (COL1A1) at 17q22. The aim of the study was to analyze the molecular characteristic of DFSP in conjunction with histopathological and clinical features.     

COL1A1-PDGFB fusion in a pediatric Bednar tumor with 2 copies of a der(22)t(17;22)

We present a 10-year-old girl with a pure Bednar tumor (pigmented dermatofibrosarcoma protuberans) of the right shoulder. Cytogenetic analysis demonstrated 47 chromosomes with 2 copies of a derivative chromosome 22, der(22)t(17;22)(q22;q13). Fluorescence in situ hybridization (FISH) analysis demonstrated the COL1A1-PDGFB fusion on both der(22) chromosomes. By RT-PCR and sequencing, we observed a fusion of the COL1A1 exon 41 with PDGFB exon 2. This pure pediatric Bednar tumor in a child, like childhood dermatofibrosarcoma protuberans, had a linear structural abnormality rather than a ring chromosome that is more commonly encountered in adult Bednar and dermatofibrosarcoma protuberans tumors. The underlying molecular abnormality in this pediatric Bednar tumor is the same as in dermatofibrosarcoma protuberans.     

Dermatofibrosarcoma protuberans of breast

We describe the case of a 57-year-old woman with a tumor of the breast suspected of being a dermatofibrosarcoma protuberans (DFSP). To confirm the diagnosis, molecular studies were performed on fixed tumor and revealed the presence of the fusion product of the COL1A1-PDGFB genes characteristic of DFSP.     

Giant cell fibroblastoma: a report of three cases with histologic and immunohistochemical evidence of a relationship to dermatofibrosarcoma protuberans

PROBLEM CONSIDERED: Giant cell fibroblastoma (GCF) is a rare mesenchymal neoplasm, which is classified as a fibrohistiocytic tumor of intermediate malignancy owing to its propensity for local recurrence, although metastasis has not been documented. Prior reports have linked GCF to dermatofibrosarcoma protuberans (DFSP), given overlapping clinical and histologic features. METHODS: This report documents three additional cases of GCF that further support the contention that this lesion is histogenetically related to DFSP. RESULTS: All three lesions occurred on the trunk of patients whose ages were 4, 28, and 38 years. One case that histologically resembled a GCF on initial excision recurred with areas of both GCF and DFSP. A second recurrence was composed entirely of DFSP. Another case contained areas of both GCF and DFSP, as well as a focus that was felt to be undergoing fibrosarcomatous change. The third case consisted entirely of GCF. Immunohistochemically, all three lesions showed intense immunoreactivity for CD34 in the GCF component. CD34 also strongly marked the cells in those cases with a DFSP component. CONCLUSIONS: Although GCF may not represent the "juvenile form" of DFSP, as previously suggested, the evidence strongly supports a histogenetic relationship between these two lesions, even though the cell of origin remains obscure.