Detection of COL1A1 -PDGFB fusion transcripts and platelet-derived growth factor α and β receptors in giant cell fibroblastoma of the postsacrococcygeal region

Selected Lesions Featuring Giant Cells

Many neoplasms of the soft tissues feature giant cells, but this article covers entities in which giant cells are a striking feature. Specifically, we consider tenosynovial giant cell tumor (localized and diffuse types; giant cell tumor of tendon sheath, and pigmented villonodular tenosynovitis), reticulohistiocytoma, juvenile xanthogranuloma, giant cell fibroblastoma (a variant form of dermatofibrosarcoma protuberans), giant cell angiofibroma (which is essentially a giant cell-rich form of solitary fibrous tumor), and phosphaturic mesenchymal tumor.

[Atypical presentation of giant cell fibroblastoma]

BACKGROUND

Giant cell fibroblastoma is a specific entity that belongs to the dermatofibrosarcoma protuberans spectrum. We report an original case with an atypical clinical presentation.

CASE REPORT

A four-year-old male child presented with a perineoscrotal mass, present since the age of one year. This lesion was initially a bluish perineal macule that grew rapidly after a traumatic injury. Physical examination showed a large flaccid bi-lobed tumour originating from the posterior border of the left of the scrotum to the anal margin. A haemolymphangioma was clinically suspected and the results of ultrasound and MRI were consistent with this diagnosis. Because of the discomfort and the atypical clinical presentation, local surgical resection was performed. Histological examination did not confirm the clinical assumption but revealed a giant cell fibroblastoma. Because of the location of this tumour, a secondary surgical procedure was carried out using the "Slow-Mohs" technique.

DISCUSSION

This case is particularly interesting because of the clinical pseudo-angiomatous presentation of this tumour. Use of the "Slow-Mohs" technique allowed sparing of tissue. No recurrence was noted after 3 years of follow-up.

Plaque-like CD34-positive dermal fibroma ("medallion-like dermal dendrocyte hamartoma"): clinicopathologic, immunohistochemical, and molecular analysis of 5 cases emphasizing its distinction from superficial, plaque-like dermatofibrosarcoma protuberans

Medallion-like dermal dendrocyte hamartoma (DH) and superficial (plaque-like) dermatofibrosarcoma protuberans (DFSP) are CD34-positive dermal neoplasms with overlapping clinicopathologic features. We analyzed the clinical, histomorphologic, and molecular criteria of 5 DH and 7 DFSP to delineate diagnostically relevant differences between incipient dermal DFSP and its benign look-alike, DH. We expand the clinical and histologic spectrum of DH. As medallion-like dermal DH is neither of dermal dendrocyte lineage nor a genuine hamartoma, we propose instead the descriptive term of plaque-like CD34-positive dermal fibroma (PDF). Both PDF/DH and DFSP presented as slightly pigmented and indurated plaques on neck, trunk, and extremities. Histologically, DFSP was characterized either by horizontally oriented spindle cell fascicles or by diffusely arranged fibroblasts within a slightly myxoid stroma in the upper two-thirds of the dermis, whereas PDF/DH presented with a cellular band-like fibroblastic proliferation mostly in the papillary and adjacent upper reticular dermis. Only one congenital PDF/DH in a 9-year-old boy extended into the septa of the subcutaneous fat. Formalin-fixed paraffin-embedded archival tissue was used for detection of the COL1A1-PDGFB gene rearrangement by multiplex reverse transcription-polymerase chain reaction (RT-PCR) and by dual color fusion fluorescence in-situ hybridization (FISH). Archival blocs older than 4 years did not yield amplifiable RNA because of RNA degradation, whereas FISH analysis was feasible in all investigated cases. FISH analysis revealed COL1A1-PDGFB gene rearrangement in all DFSP cases (n=7), whereas RT-PCR could detect the COL1A1-PDGFB fusion transcript only in 1 DFSP. Two cases were negative. In 4 archival cases with storage between 4.5 and 12 years, RNA had been degraded making these cases unsuitable for RT-PCR. In PDF/DH, both RT-PCR and FISH analysis did not reveal any evidence of COL1A1-PDGFB gene rearrangement. We show that PDF/DH and superficial (plaque-like) DFSP, subtle clinicopathologic differences notwithstanding, are morphologic look-alikes that can be kept apart by molecular studies of the COL1A1-PDGFB gene fusion. For the detection of the COL1A1-PDGFB gene rearrangement in diagnostically difficult cases, RT-PCR and FISH analysis are reliable and helpful diagnostic tools. In archival formalin-fixed paraffin-embedded tissue, however, FISH analysis is more robust and exhibits a higher clinical sensitivity than RT-PCR.

Platelet-derived growth factor receptor alpha mutational status and immunohistochemical expression in Merkel cell carcinoma: implications for treatment with imatinib mesylate

BACKGROUND

It is not known if Merkel cell carcinomas (MCCs) show mutations in the platelet-derived growth factor receptor alpha (PDGFRA) gene similar to a subset of gastrointestinal stromal cell tumors. The purpose of this study was to analyze MCCs for mutations in the PDGFRA gene as well as to analyze those MCCs exhibiting a possible mutation in the PDGFRA gene for immunohistochemical expression of PDGFRA.

METHODS

We extracted tumor DNA from nine MCCs, performed polymerase chain reaction amplification of PDGFRA exons 10, 12, 14 and 18, and directly sequenced those gene products for mutations. In addition, we evaluated for PDGFRA immunostaining in three MCCs showing a possible PDGFRA gene mutation.

RESULTS

Three out of nine (33.3%) MCCs showed an identical novel single heterozygous base change in exon 10 of the PDGFRA gene leading to an amino acid substitution at codon 478. In addition, all three (100%) of those MCCs expressed PDGFRA.

CONCLUSIONS

Although it is unknown whether the base change described above represents a true mutation or a single nucleotide polymorphism, the fact that this change was absent in our control specimens suggests that this mutation may be oncogenic in nature and may make imatinib mesylate a possible therapeutic option in MCC.