The remainder of cases present as sPCL: leukemic transformations of relapsed or refractory myeloma that affect up to 4% of myeloma patients, although incidence rates of sPCL appear to be climbing, note authors of the new consensus recommendations. Relatively little is known about the epidemiology of PCL, but it appears to be more common among African Americans than Caucasians (as is also the case for myeloma), they write.

“pPCL is observed in younger patients than multiple myeloma (MM), with an increased incidence of light-chain only (Bence Jones) type,” the consensus recommendations state. “The clinical picture is characterized by an aggressive clinical presentation with high tumor burden, high proliferative index (that is, S-phase DNA), rapid clinical course, leukocytosis, extramedullary involvement, marked bone marrow infiltration by immature plasma cells and high LDH serum levels. Finally, the presentation of relapsed pPCL routinely mimics the initial clinical picture.”

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Diagnostic Criteria Recommendations

Diagnostic criteria were originally published in 1974, involving circulating plasma cells of 20% or higher and an absolute count greater than 2 x 109 plasma cells per liter in peripheral blood. These criteria have not been studied prospectively to identify possible changes and “(p)robably only one of these criteria should be sufficient for the diagnosis” of PCL, the Working Group notes.

It is “important to recognize that the presence of circulating plasma cells is not always indicative of PCL, as the presence of a significant number of polyclonal peripheral blood plasma cells can be transiently observed in non-malignant conditions, such as severe sepsis, infectious mononucleosis, and particularly, serum sickness,” they write.

The consensus recommendations for diagnosis include careful conventional microscopic examination of peripheral blood for all patients with myeloma who present with suspected PCL (e.g., leukocytosis and elevated LDH), the Working Group recommends.

“If there are more than 20% circulating plasma cells and/or an absolute count greater than 2 x 109/L plasma cells, the diagnosis of PCL should be established” but lower peripheral blood plasma counts (≥5% peripheral blood plasma cells and/or an absolute number ≥0.5 x 109/L) should be recorded” to revisit PCL diagnosis.

The distinct biology of PCL from MM offers additional diagnostic criteria, the authors concluded.

“Plasma cells from patients with PCL overlap in antigenic expression with those of patients with MM,” they write. “However, CD20 (higher), CD56 (lower), CD117 (lower), and HLA-DR (lower) may be useful for both discrimination of PCL and MM and for follow-up studies.”

Further research should be undertaken to assess inclusion of flow cytometry for early detection of PCL and the pathogenic role of surface cell molecules driving extramedullary spread, the authors urge.

The consensus statement on PCL diagnosis also implores “mandatory” cytogenetic and FISH studies on bone marrow.

“On cytogenetics, the karyotype is frequently complex and demonstrates hypodiploidy,” they note. “With FISH analysis, careful attention should be paid to the most frequently reported alterations: (t(11;14) as well as to chromosome 1 and 17 abnormalities, particularly 1q+ and del17p.”