ACCURACY OF IMMUNOHISTOCHEMISTRY AND FLOW-CYTOMETRY IN ESTIMATING THEPROPORTION OF LEUKEMIC-CELLS IN S-PHASE IN CHRONIC MYELOID-LEUKEMIA PATIENTS

We compared the proportion of S phase cells in bone marrow end periphe ral blood samples obtained from 17 patients with chronic myeloid leuke mia (CML). Before sampling all patients received a one hour IV infusio n of iododeoxyuridine (IdUrd). The proportion of S phase cells was stu died by immunohistochemistry (IHC) in bone marrow biopsies, and by flo w cytometry (FCM) in bone marrow aspirates and peripheral blood sample s. The IdUrd labelling index (LI) in bone marrow biopsy sections (27.5 +/- 1.8%) was significantly higher than the proportion of IdUrd label led cells in bone marrow aspirate (15.1 +/- 2.0%). The percentage of S phase cells in peripheral blood was approximately the same as that in the aspirate (12.4 +/- 1.3%) and was correlated with that of bone mar row aspirate indicating a high degree of the aspirate dilution by peri pheral blood. It is likely that the differences in % S phase cells in the aspirate and the biopsy result from this dilution. Estimates of th e % S phase cells in the peripheral blood study by IHC and FCM were es sentially the same. Samples labelled for one hour in vitro resulted in 1.5 fold higher LI than the same samples labelled in vivo. We conclud e that estimates of the 8% S phase cells in the bone marrow of patient s with CML should be made by infusing patients with IdUrd or BrdUrd wi th immunohistochemical evaluation of a marrow biopsy, Additionally in vitro labelling is not reflective of the percent S phase cells in vivo in patients.