A landscape effect in tenosynovial giant-cell tumor from activation of CSF1 expression by a translocation in a minority of tumor cells

Abstract

Tenosynovial giant-cell tumor (TGCT) and pigmented villonodular synovitis (PVNS) are related conditions with features of both reactive inflammatory disorders and clonal neoplastic proliferations. Chromosomal translocations involving chromosome 1p13 have been reported in both TGCT and PVNS. We confirm that translocations involving 1p13 are present in a majority of cases of TGCT and PVNS and show that CSF1 is the gene at the chromosome 1p13 breakpoint. In some cases of both TGCT and PVNS, CSF1 is fused to COL6A3 (2q35). The CSF1 translocations result in overexpression of CSF1. In cases of TGCT and PVNS carrying this translocation, it is present in a minority of the intratumoral cells, leading to CSF1 expression only in these cells, whereas the majority of cells express CSF1R but not CSF1, suggesting a tumor-landscaping effect with aberrant CSF1 expression in the neoplastic cells, leading to the abnormal accumulation of nonneoplastic cells that form a tumorous mass.

Fig. 1.

RTK expression in 507 soft-tissue tumors. Tumors are grouped along the y axis by diagnosis. Results of ISH using four RTK antisense probes: CSF1R, KIT, PDGFRA, and PDGFRB and one ligand, CSF1, are shown on the x axis. Bright red, strong expression; dark red, weak expression; green, no expression; white, no data as a result of tissue loss.

Fig. 2.

CSF1 and CSF1R ISH in TGCT. (A) CSF1R ISH in TGCT; dark granules denote sites of hybridization. All scorable TGCT and PVNS were positive for CSF1R mRNA expression in the vast majority of cells. (B) CSF1 ISH in TGCT. All CSF1-positive cases of TGCT and PVNS showed similar low numbers of cells expressing CSF1.

Fig. 3.

FISH on TGCT. (A) FISH with the CSF1-spanning BAC probe RP11–19F3B on TGCT confirms that the CSF1 gene is split by the translocation in TGCT. (B) The fusion of CSF1 and COL6A3 was confirmed by FISH. The COL6A3 locus is represented by CTD-2344F21 (labeled in white), the region telomeric to CSF1 is represented by RP11–96F24 (labeled in green), and the region centromeric to CSF1 is represented by RP11–354C7 (labeled in orange). (C) In metaphase TGCT, FISH with BAC probe RP11–25803 that covers the region telomeric to COL6A3, which fails to split. (D and E) Two nuclei with the fusion of CSF1 and COL6A3 demonstrated by FISH on interphase TMA sample of TGCT. The COL6A3 locus is represented by CTD-2344F21 (labeled in white), the region telomeric to CSF1 is represented by RP11–96F24 (labeled in green), and the region centromeric to CSF1 is represented by RP11–354C7 (labeled in orange). (F) Lack of translocation in a nucleus from the same sample as D and E shows an intact CSF1 gene. (G) Combined interphase FISH with the region telomeric to CSF1 represented by RP11–96F24 (labeled in green) and the region centromeric to CSF1 represented by RP11–354C7 (labeled in orange), and CSF1 immunohistochemistry (labeled in red) demonstrated that only the cells with the translocation expressed CSF1.

Fig. 4.

Unsupervised hierarchical clustering of seven cases of PVNS (in red), six cases of TGCT (purple), six cases of SFT (blue), and seven cases of DTF (green) based on expression profiling with DNA microarrays. In the heatmap, red represents high expression, black represents median expression, green represents low expression, and gray represents no data.

Fig. 5.

Double staining for CSF1 mRNA and CD163 or CD68 protein in TGCT. (A) CD163 immunohistochemistry (DAB). (B) CSF1 ISH with fluorescence (red). (C) Combined A and B; CSF1 ISH with fluorescence (red) and CD163 immunohistochemistry (DAB). (D) CD68 immunohistochemistry with fluorescence (red). (E) CSF1 ISH with fluorescence (green). (F) Combined D and E; CSF1 ISH with fluorescence (green) and CD68 immunohistochemistry with fluorescence (red).

Fig. 6.

CSF1 ISH in reactive synovitis, showing strong reactivity in synovial-lining cells.

Fig. 7.

Autocrine and paracrine scheme for CSF1 landscaping effect. CSF1 is produced by neoplastic cells, with translocation resulting in increased numbers of neoplastic cells through an autocrine loop with CSF1R. CSF1 also recruits nonneoplastic CD163- and CSF1R-expressing cells of monocyte/macrophage lineage.