Answer is B (Plasmacytoma) Presence of a solitary lytic lesion of the bone with monoclonal plasma cells suggests a diagnosis of Solitary Plasmacytoma of Bone. A small M spike may be identified in some patients but Bone Marrow biopsy taken some distance away from the primary site is typically not involved typically showing < 10 percent plasma cells Solitary Bone Plasmacytoma The diagnosis of SBP requires histologic evidence of a monoclonal plasma cell infiltrate in a single bone lesion, absence of other bone lesion on skeletal survey, and lack of marrow plasmacytosis elsewhere. Fuhermore, there should be no evidence of anemia, hypercalcemia, or renal dysfunction that could be attributed to the plasma cell proliferative disorder spike may be identified in some patients hut Bone Marrow biopsy taken some distance away from the primary site is not involved typically showing < 10 percent plasma cells. Diagnostic criteria for Solitary Plasmacytoma of bone and Extramedullary Plasmacytoma Solitary Osseous lesion or Extramedullary lesion due to clonal plasma cell proliferation Normal marrow with no evidence of clonal plasma cells or aneuploidy by flow-cytometry. Normal skeletal survey with proximal humeri and femora and a Normal magnetic resonance image of the axial skeleton (for Solitary Plasmacytoma of Bone); or a Normal regional computed tomographic scan (for Extramedullary Plasmacytoma). Absent or low serum or urinary concentration of monoclonal protein. No anemia, hypercalcemia, or renal insufficiency attributable A myeloma.