FOXP1 expression in monoclonal gammopathy of undetermined significance and multiple myeloma.

Multiple myeloma (MM) is a clonal disorder of terminally differentiated B cells. In some cases the premalignant state is monoclonal gammopathy of undetermined significance (MGUS). Neoplastic plasma cells in both entities carry multiple and complex chromosomal abnormalities that make understanding of the disease development difficult. New insight into malignant mechanisms that underlie multiple myeloma may come from forkhead box P1 transcription factor (FOXP1) analysis in neoplastic plasma cells. FOXP1 is known to be important for B-cell maturation and differentiation and could play a significant role in plasma cell tumors. The purpose of the present study was therefore to analyze FOXP1 protein presence and FOXP1 gene abnormalities in 13 cases of MGUS and 60 cases of MM. It was found that FOXP1 protein was expressed in neoplastic plasma cells, unlike in their normal counterparts, and that additional FOXP1 gene copies could be found in both MGUS and MM. Based on FOXP1 presence in MM and its role in diffuse large B-cell lymphoma and extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue, FOXP1 might play an important role in plasma cell neoplasm.