Biphenotypic plasma cell myeloma: two cases of plasma cell neoplasm with a coexpression of kappa and lambda light chains

Abstract

Plasma cell neoplasm (PCM) is a medullary and extra medullary proliferation of clonal plasma cells that occurs due to accidental translocation of proto-oncogenes into immunoglobulin (Ig) gene loci. While the majority of plasma cell neoplasms are monoclonal, up to 2% of the PCMs [1] considered being biclonal based on electrophoretic analysis, characterized by secretion of paraprotein with two distinct heavy chains or light chains are possible and present unique diagnostic challenges.

Methods: Traditionally protein electrophoresis has been used to diagnose, characterize, and monitor progression of plasma cell neoplasm. To characterize neoplastic plasma cells, in our institution, other ancillary studies, including in situ hybridization, flow cytometric analyses of plasma cell surface markers and cytoplasmic immunoglobulins with DNA ploidy, are also utilized routinely.

Results: We present two cases of plasma cell myeloma in which the neoplastic plasma cells shows production of cytoplasmic kappa and lambda light chain, with secretion of free lambda light chain only. Co-expression of kappa and lambda light chain by the same neoplastic plasma cells is a rare but reported phenomenon.

Conclusions: Our study indicates that serum electrophoresis alone could mischaracterize biphenotypic myeloma as monotypic plasma cell myelomas in the absence of additional testing methods.

Keywords: Biphenotypic plasma cell myeloma; light chain coexpression.

Figure 1

Plasma cell myeloma expressing IgG heavy chain with co-expression of kappa and lambda light chain. (A) Hematoxylin and eosin stain showing diffuse infiltration of bone marrow by myeloma cells. (B) Immunohistochemical staining of bone marrow biopsy showing diffuse positive staining for CD138. (C) and (D) In-situ hybridization detecting kappa and lambda light chain mRNA in bone marrow biopsy.

Figure 2

Multi-parameter im munophenotypic flow cytometric analysis showing cytoplasmic co-expression of kappa and lambda light chain protein by CD38, CD56 and CD138 positive neoplastic plasma cells.

Figure 3

Flow cytometric analysis of bone marrow aspirate to asses DNA contents showing diploid (normal) and hyperdiploid (neoplastic) cell population (A). Note the presence of cytoplasmic kappa(B) and lambda(C) light chain by hyperdiploid cells.

Figure 4

Plasma cell myeloma expressing IgG heavy chain with co-expression of kappa and lambda light chain. (A)Hematoxylin and eosin stain showing diffuse infiltration of bone marrow by myeloma cells. (B) Immunohistochemical staining of bone marrow biopsy showing diffuse positive staining for CD138. (C) and (D) In-situ hybridization detecting kappa and lambda light chain mRNA in bone marrow biopsy.

Figure 5

Multi-parameter flow cytometric analysis showing cytoplasmic co-expression of kappa and lambda light chain protein by CD38, CD45 (dim) and CD138 positive neoplastic plasma cells.

Figure 6

Flow cytometric analysis of bone marrow aspirate to asses DNA contents showing diploid (normal) and hyperdiploid (neoplastic) cell population (A). Note the presence of cytoplasmic kappa (B) and lambda (C) light chain by hyperdiploid cells.