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Langerhans Cell Histiocytosis (LCH) is characterized by the presence of destructive granulomas containing CD1a+ Langerhans-like dendritic cells, lymphocytes and eosinophils. LOH at several loci as well as DNA copy number changes on chromosomes 1, 5, 7, 9, 13, 16 and 18 were described in LCH lesions of bone (Murakami et al, Human Pathol. 33, 555, 2002). To identify additional changes of pathogenetic importance, we determined the copy number in situ and possible rearrangement of the c-myc, CCND1 (cyclin D), Her-2/neu and p53 proto-oncogenes in LCH of bone. LCH cell suspension was obtained after collagenase treatment of the granulomas (n=7) and cytocentrifuge smears on slides were prepared. LCH-derived stromal cell lines, DOR-1 and PRU-1, carrying the translocations t(9;17) and t(6 ;12) were used for comparison. Fluorescence in situ hybridization (FISH) was performed with centromeric probes for chromosomes 1, 5, 7, 8, 11, 17 and 22 and locus identifying probes for c-myc, CCND1, Her-2/neu and p53 proto-oncogenes. expression of oncoproteins and mRNAs was performed by immunocytochemistry and Northern blot. By FISH analysis, consistent levels of amplification of c-myc and Her-2/neu (between 5 to 14 copies per nucleus) was found in 3 of 7 cases, corrected for aneusomies 8 and 17. Low level of amplification of Her-2/neu was revealed in 2 samples. The fraction of nuclei with c-myc and Her-2/neu amplification ranged between 16% and 23% and was associated with large bone lytic lesions. In two samples, an increased number of CCND1 copies with CCND1-to-chromosome 11 signal ratios > 2 were revealed in more than 28% of nuclei. None of the lesions exhibited amplifications of p53 gene. The LCH derived cell lines DOR-1 and PRU-1 showed strong amplification of c-myc (7–23 copies) in 21% and 17% of the nuclei, CCND1 (4 –9 copies) in 21 % and 12% and of Her-2/neu (7–12 copies) in 21 and 15% of the nuclei respectively. The presented results demonstrate an alteration of c-myc, CCND1 and Her-2/ neu genes copy number in LCH lesions of bone. Structural changes of cell cycle related proto-oncogenes support the neoplastic origin of distinct subtypes of histiocytic lesions arising in bone.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]