Plasma cell immunophenotype and clonality.

Plasma cell involving the bone marrow replaced the normal bone marrow and disrupted the bone trabeculae (A, × 200). Neoplastic plasma cells often infiltrated the perispinal tissues and ganglions (B, × 200) and in some cases invaded the central nervous system (C, × 200). NPM-ALK was largely confined within the cytoplasm of the neoplastic plasma cells (D, × 400). Tumor cells were invariably CD138⁺ (E, × 400), displayed a variable number of Ki-67⁺ cells (F, × 400) and they expressed clonotype heavy and light immunoglobulin determinants (G, × 100). The serum analysis also demonstrated the presence of free light chain immunoglobulin (H-I).