Prognostic significance of the S-phase fraction of light-chain-restricted cytoplasmic immunoglobulin (clg) positive plasma cells in patients with newly diagnosed multiple myeloma enrolled on Eastern Cooperative Oncology Group treatment trial E9486

The bone marrow plasma cell labeling index (PCLI) as measured by bromodeoxy uridine uptake is a well-established independent prognostic factor for pati ents with newly diagnosed multiple myeloma, but the test is not easily done in most laboratories, The purpose of this study was to determine if the pr oliferative activity (% S-phase) as determined by two-color flow cytometry for cytoplasmic immunoglobulin (clg) light chain and DNA content also had p rognostic significance. As part of Eastern Cooperative Oncology Group clini cal trial E9486, 500 patients had successful performance of the bone marrow PCLI. Of 349 patients who had flow clg and DNA content cytometry, 210 had adequate data to reliably calculate S-phase %. Patients with low % S-phase fraction (<2%) had a significant overall survival advantage over patients h igh % S-phase fraction (greater than or equal to 2%), median survivals 4.1 vs. 2.9 years (P = 0.032). Measurement of the S-phase % by flow cytometry g ives significant prognostic information in patients with newly diagnosed my eloma. However, in multivariate analysis, S-phase % did not add prognostic information when PCLI was in the model. S-phase % added prognostic informat ion only when all cases with flow measurement of S-phase % were included, a nd when PCLI was excluded from the model, Discriminating a population of on ly clg positive cells proved difficult in patients with a low percentage of bone marrow plasma cells. Methodology to measure S-phase % in patients wit h a low percent plasma cells is needed before this technique can be used fo r diagnosis and prognosis in myeloma. (C) 1999 Wiley-Liss, Inc.