Changes in spontaneous SCE frequencies as a function of sampling time in lymphocytes from normal donors and cancer patients.

Spontaneous SCE frequencies were measured in cells undergoing their second mitosis at 54, 68, 72, 78 or 90 h after PHA stimulation of whole blood cultures from 7 normal donors. A consistent pattern of fluctuation of SCE levels was observed between 54 and 78 h. The magnitude of change in SCE frequency between consecutive fixation times was as high as 80% for some donors. These observations support the hypothesis of Snope and Rary (1979) that there are subpopulations of lymphocytes with different spontaneous SCE levels and different proliferation rates. In untreated cancer patients the patterns of change in SCE frequency with time were different from that seen in normal donors. This may be because of quantitative changes in T-lymphocyte sub-populations which have been observed in cancer patients. Changes in SCE frequency of less than about a factor of two, observed at a single sampling time may not be indicative of genotoxic events or genetic instability but simply represent changes in the composition of lymphocyte sub-populations and/or in their rates of proliferation in vitro.