Reappraisal of plateau phase in myeloma.

The frequency with which the plateau of stable phase occurs after remission-induction chemotherapy, and the kinetic features of this phase, were evaluated in 127 carefully staged patients with multiple myeloma. 56 patients (44%) entered a stable plateau state, this pattern being most common in patients with stages IA, IIA, and IIIA of the disease, and least likely in those with stages IIB or IIIB, especially those with Bence Jones protein only or Bence Jones protein plus a serum M-component. Tritiated thymidine labelling index (LI) of bone-marrow myeloma cells, polyamine measurements, and in-vitro myeloma stem-cell culture findings all indicated that the plateau phase is a cytokinetically quiescent state, compared with the more active induction and relapse phases. The major implications of these findings include the avoidance of aggressive "cycle active" treatment and discontinuation of maintenance treatment in plateau-phase patients.