Primary extramedullary plasmacytoma: similarities with and differences from multiple myeloma revealed by interphase cytogenetics.

Primary extramedullary plasmacytoma is an indolent neoplasm that infrequently converts to multiple myeloma. Since cytogenetic data on extramedullary plasmacytoma are lacking, we studied 38 cases of this type of neoplasm by fluorescence in situ hybridization. Fourteen cases (37%) contained IGH breaks, including six with a t(4;14) translocation. No translocations t(11;14), t(14;16), t(8;14), nor breaks involving MALT1, BCL6 or FOXP1 were found. Loss of 13q (40%), as well as chromosomal gains (82%) were common. There was no correlation between chromosomal alterations and clinical features or local relapse. Cytogenetically, extramedullary plasmacytoma and multiple myeloma are closely related. However, the distribution of IGH translocation partners, with the notable absence of t(11;14), is different. Key words: extramedullary plasmacytoma, multiple myeloma, cytogenetics, IGH translocation, fluorescence in situ hybridization.