Primary Plasma Cell Leukaemia and Autologous Stem Cell Transplantation.

Introduction: Primary plasma cell leukaemia (PCL) is a rare disorder representing less than 5% of malignant plasma cell disease and is associated with a poor prognosis with median survivals in PCL reported at 8 to 12 months, significantly shorter than for Multiple Myeloma even when the comparison is adjusted to compare only with Multiple Myeloma of high tumour mass. Treatment of PCL with alkylating agent-based therapy is ineffective and while polychemotherapy may offer improved survival, results remain disappointing with a few exceptions. Autologous transplantation is now being used widely in the treatment of these patients and this report summarises the European Blood and Marrow Transplant (EBMT) experience of this disorder.

Patients and Methods: A retrospective study was carried out with 20844 patients with common type multiple myeloma (58% IgG, 21% IgA and 19% light chain types only) and 272 patients with primary plasma cell leukaemia who underwent first autologous transplantation between 1980 and 2006. All patients were reported to the EBMT registry using MED-A (limited data set) or MED-B (more extensive data set) forms. All autografted patients were included in the study regardless of the availability of complete MED-A or MED-B data. The proportion of patients that could be evaluated for each parameter was noted and the number of evaluable patients included in the result. Comparisons between the two groups were made using Chi-squared test for categorical data and the Mann-Whitney test for continuous data. Overall Survival and Progression-Free Survival were calculated using the Kaplan-Meier method and comparisons were made using the Log-Rank test. Relapse/Progression and Death without relapse or progression probabilities were computed by the proper non-parametric estimator for outcomes with competing risks and compared by the Gray test.

Results: There were no significant differences in age and gender of the PCL and myeloma groups. Calcium and albumin were also not significantly different, however, haemoglobin was significantly lower in the PCL group (11g/dl versus 9g/dl - P=0.000) while creatinine was significantly higher in the PCL group - 92 micro mol/l versus 122 micro mol/l - P=0.000). B₂ microglobulin was significantly higher in the PCL group which tends to be diagnosed with a more advanced disease. There was no difference in the type of graft used or in the use of total body irradiation but the PCL group were transplanted within a shorter time from diagnosis (6.0 v 7.7 months - P=0.000). While there was no significant difference in engraftment, PCL patients were more likely than myeloma patients to enter CR post-autologous transplantation. Despite this, overall survival for the PCL patients was greatly inferior to the myeloma patients - 62.3 months (CI 60.4–64.3) versus 25.7 months (CI 19.5–31.9 - P=0.000). Poor survival is accounted for by an increase in relapse-related mortality and post-transplant responses of short duration.

Conclusion: This is the largest study of plasma cell leukaemia patients ever reported. Our data shows an improved outcome for these patients with use of autologous transplantation but undoubtedly this transplant group represents the fittest of such patients and their outcome is still greatly inferior to comparable myeloma patients.