Differential diagnosis of primary cutaneous CD4+ small/medium T-cell lymphoproliferative lesions: A report of three cases

with a specific myeloma immunoglobulin type, although a more aggressive course is observed in light-chain-only subtypes [10]. Requena et al. [11] analyzed 8 cases of cutaneous plasmacytoma and revealed that malignant plasmacytes are homogeneous in their immunophenotype with strong expression of CD79a, CD138, and epithelial membrane antigen. In addition, RB1 gene deletion in skin-infiltrated plasmacytes was reported to be associated with poor prognosis [11]. A recent retrospective study of 53 cutaneous plasmacytoma cases showed no correlation between CD56 negativity or cytogenetic abnormality with skin infiltration of malignant plasma cells and that the plasmablastic morphology in the skin lesion indicated a worse overall survival [10]. In the present case, the malignant plasma cells were positive for CD138 and negative for CD56, CD19, CD20, and CD22, which correlated to the immunophenotypic characterization of malignant plasma cells. The RB1 gene deletion could not be analyzed, and no significant plasmablastic appearance of plasma cell infiltration was observed in the patient’s skin lesion. Although hemophagocytosis by neoplastic plasma cells has rarely been described in the literature, this rare condition does not appear to be associated with a specific immunophenotype, immunoglobulin or light-chain subtype, or karyotype [6]. One hypothesis is that hemophagocytic plasma cell formation may be attributed to the expansion of rare B-cell clones with innate phagocytic potential, although this proposition remains to be confirmed [5, 7]. Similar to our case, the hemophagocytic feature of plasma cells is more frequently found in female patients, and it appears to be dominant in mature erythrocytes and platelets [4, 7]. Some reports also suggest that phagocytosis by neoplastic plasma cells resulted in peripheral blood cytopenia; however, whether this complication is a direct consequence of hemophagocytosis by plasma cells remains to be determined [2, 4].