Insights into extramedullary tumour cell growth revealed by expression profiling of human plasmacytomas and multiple myeloma Cyrus V. Hedvat, 1,2 Raymond L. Comenzo, 3 Julie Teruya-Feldstein, 2 Adam B. Olshen, 4 Scott A. Ely, 5 Keren Osman, 3 Yana Zhang, 3 Nagesh Kalakonda 1 and Stephen D. Nimer 1,3 1 Laboratory of Molecular Aspects of Hematopoiesis, Sloan Kettering Institute, 2 Department of Pathology, 3 Division of Hematologic Oncology, Department of Medicine, 4 Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA, and 5 Department of Pathology, Weill Medical College of Cornell University, New York, NY Received 4 March 2003; accepted for publication 21 April 2003 Summary. Malignant plasma cells generally grow within the bone marrow microenvironment; however, they can also grow at extramedullary sites. To identify the tumour- specific alterations required for extramedullary growth, we analysed the expression profiles of a series of plasma cell neoplasms including primary multiple myeloma (MM), plasma cell leukaemia (PCL) and extramedullary plasma- cytoma (EPC). Hierarchical clustering analysis segregated the EPCs from the remaining samples, and revealed an expression pattern associated with angiogenesis in the EPCs, involving higher expression of the genes TIE2, NOTCH3, CD31 and endoglin. Direct comparison of EPC samples with the MM samples identified 156 genes significantly upregu- lated and 85 genes significantly downregulated (P <0®005, t-test) in the EPCs, including several genes involved in angiogenesis and adhesion that were upregulated (inclu- ding angiopoietin 1, SPARC, Notch3 and fibronectin 1). Immunohistochemical staining demonstrated CD31 and endoglin protein expression in the EPC tumour cells, which are both angiogenesis related and could confer malignant plasma cells with the ability to grow outside the normal bone marrow environment. Defining how malignant plas- ma cell growth is regulated in the bone marrow versus at extramedullary sites will help to delineate the mechanisms underlying the dependence of tumour cell growth on angiogenesis and cell adhesion. Keywords: multiple myeloma, angiogenesis, gene arrays, myeloma, myeloma cell lines. Plasma cell dyscrasias represent a spectrum of diseases that includes clinically benign conditions, such as monoclonal gammopathy of unknown significance (MGUS), and malig- nant diseases, including multiple myeloma (MM) and its more aggressive form, plasma cell leukaemia (PCL). Extra- medullary plasmacytomas (EPC) are collections of clonal plasma cells that grow outside the bone marrow and constitute 3–5% of all plasma cell neoplasms (Kapadia et al, 1982). EPCs can occur with or without concomitant bone marrow involvement by clonotypic plasma cells. MM is an incurable and fatal disease, constituting approximately 10% of the haematological malignancies that occur in the United States each year. MM cells can communicate with diverse cell types and extracellular matrix (ECM) components within the bone marrow micro- environment. Paracrine interactions with stromal cells sustain the survival and growth of malignant plasma cells, whereas myeloma cell-triggered osteoclast activation results in the characteristic osteolytic lesions that accompany the disease. Expression of adhesion molecules by myeloma cells may contribute to disease progression (Shain et al, 2000), and the integrin family of cell adhesion molecules, which cells use to interact with ECM components, has been implicated in the pathogenesis and course of myeloma (Sanz-Rodriguez et al, 2001). For example, myeloma cell adhesion to fibronectin can prevent chemotherapy-induced cell death of myeloma cell lines (Damiano et al, 2001), and such interactions may contribute to myeloma cell expan- sion and drug resistance. Tumour growth is dependent on angiogenesis, and several of the factors that regulate this process can be Correspondence: Stephen D. Nimer, Memorial Sloan Kettering Cancer Center, Division of Hematologic Oncology, 1275 York Ave., New York, NY 10021, USA. E-mail: nimers@mskcc.org British Journal of Haematology, 2003, 122, 728–744 728 Ó 2003 Blackwell Publishing Ltd