Growth kinetics of plasma cell myeloma.

The plasma cell labeling index(ex) (LI) of 128 patients with multiple myeloma at various stages of disease was compared as a function of tumor mass load and length of treatment. No significant differences in LI were noted for patients with various degrees of tumor reduction. Patients observed during the first 3 months of treatment had significantly higher LI than did untreated patients and those studied after longer intervals. In vivo cell-cycle analysis of myeloma cells by the halving time of the grain-count method failed to establish the length of the cell cycle but defined the length of S+G2 phases as being longer than 60 hours. Similar studies conducted in vitro defined a shorter combined length of S+G2 phase. In 2 patients in whom continuous infusion with [3H] thymidine was performed, the generation time was established as 8 days. Both patients had similar initial LI (5.7 and 6.6) but different growth fractions (19 and 47%). The measured tumor mass doubling time was much longer than the calculated one, suggesting the presence of considerable intrinsic cell loss (83 and 47%). These observations were summarized by a hypothetical two-compartment model for the growth kinetics of multiple myeloma.