title: IgM multiple myeloma: pathologic evaluation of a rare entity.
abstract: OBJECTIVE
  To delineate the pathology of immunoglobulin M-producing multiple myeloma (IgM MM).
  
  
  METHODS
  Clinicopathologic data were reviewed for 15 cases meeting World Health Organization criteria for MM and having a serum IgM paraprotein. Immunohistochemistry was performed on diagnostic bone marrow specimens for common B-cell and plasma cell markers.
  
  
  RESULTS
  Of the 15 IgM MM bone marrows reviewed, 6 (40%) had lymphoplasmacytoid cytology, and 12 (80%) expressed CD19, CD20, and/or CD45. Cyclin D1 expression was common (11 cases, 73%) and usually associated with t(11;14). No cases expressed CD5 or had an associated CD5-positive B-cell population. CD117 was positive in 20% of cases.
  
  
  CONCLUSIONS
  The frequent B-cell-associated antigen expression by IgM MM distinguishes it from other MM types, causing significant pathologic overlap with lymphoplasmacytic lymphoma (LPL). However, IgM MM is usually distinguished from LPL by aberrant cyclin D1 expression or t(11;14). Therefore, assessing for these abnormalities is recommended when evaluating bone marrow involvement by IgM-associated lymphoplasmacytoid disorders.
authors.affiliation: Dept of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, 34th and Civic Center Blvd, Philadelphia, PA 19104; e-mail: rebecca.king98@gmail.com.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: King
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Howard
authors.forename: Janice M
authors.initials: JM
authors.lastname: Hodnefield
authors.forename: William G
authors.initials: WG
authors.lastname: Morice
mesh_terms: D000368:Aged; D001402:B-Lymphocytes / Q000378:metabolism / Q000473:pathology; D014408:Biomarkers, Tumor / Q000378:metabolism; D001853:Bone Marrow / Q000473:pathology; D002880:Chromosomes, Human, Pair 11; D002883:Chromosomes, Human, Pair 14; D019938:Cyclin D1 / Q000378:metabolism; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D010265:Paraproteinemias / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D035583:Rare Diseases; D014178:Translocation, Genetic
chemical_list: D014408:Biomarkers, Tumor; C530104:CCND1 protein, human; D007075:Immunoglobulin M; D019938:Cyclin D1
keywords: Cyclin D1; IgM multiple myeloma; Immunophenotype; Lymphoplasmacytic lymphoma; Pathology