THE SIGNIFICANCE OF LIGHT CHAIN-RESTRICTED BONE-MARROW PLASMA-CELLS AFTER PERIPHERAL-BLOOD STEM-CELL TRANSPLANTATION FOR MULTIPLE-MYELOMA

While plasmacytosis is a common occurrence in early post-bone marrow t ransplantation biopsy specimens, the significance of plasma cells in s uch specimens from patients with multiple myeloma (MM) is unknown. We attempted to retrospectively determine, by morphologic assessment of p lasma cell percentage, immunohistologic assessment of plasma cell ligh t chain ratio (LCR), and correlation with clinical outcome, the preval ence and significance of plasmacytosis in the posttransplantation bone marrow biopsy specimens of 25 patients with MM who underwent autologo us peripheral blood stem cell transplantation (PBSCT). No pre-PBSCT mo rphologic or immunologic characteristics were significantly associated with the post-PBSCT outcome in this group of patients. While 9% of al l biopsy specimens and 25% of hypocellular biopsy specimens obtained d uring the first 60 days after the PBSCT contained more than 10% plasma cells, 34% of all biopsy specimens obtained during this period had el evated LCRs. The dominant light chain in all cases with high LCRs was the same as that of the original tumors, implying that these plasma ce lls represent a portion of the patients' original tumors. However, the presence of tumoral plasma cells during the early post-PBSCT period w as not associated with outcome (P>.5 at 30 days and 60 days after tran splantation). Histologic features of recurrent MM and elevated LCR occ urring at day 90 or later are correlated with progression of disease ( P=.02 and P=.0001, respectively). We conclude that the presence of tum oral plasma cells in the early post-PBSCT period likely represents res idual tumor and should not be regarded as indicating imminent relapse, while the presence of tumor as assessed by histologic or immunohistoc hemical evaluation during the late post-PBSCT period should raise the concern of relapse and disease progression.