Lacking CD56 expression in a relapsing cutaneous blastic plasmacytoid dendritic cell neoplasm after allogeneic bone marrow transplantation: FISH analysis revealed loss of 11q

Background Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare entity characterized by a CD4+/CD56+/CD123+ immunophenotype and a fatal clinical course. The average survival of 12–14 months may be prolonged by allogeneic bone marrow transplantation (BMT). Objectives We report about a male patient who suffered from BPDCN with a typical histology and co-expression of CD4/CD123 and a CD56 expression by 80% of the tumour cells. The cutaneous tumour relapse after chemotherapy and allogeneic BMT was completely negative for CD56. Methods We performed interphase fluorescence in situ hybridization (FISH) analysis of tumour tissue, asserved before and after BMT, using specific probes for chromosome 11, which encompass the CD56 gene region. Results The tumour cells revealed a partial loss of 11q as well as a monosomy of chromosome 11. Conclusion This case demonstrates for the first time that loss of CD56 expression can also occur as a secondary event after chemotherapy and BMT. In our case, DNA loss of 11q23 could be responsible for the negativity of 20% of tumour cells as observed before chemotherapy. However, the complete loss of CD56 expression in the relapsed tumour cannot be explained by the loss of 11q23 alone. Additional factors such as chemotherapy-induced mutations might also have contributed.