[Show abstract][Hide abstract] ABSTRACT: Thirty-eight previously untreated patients with a histologically proved diagnosis of nasopharyngeal carcinoma were evaluated for in vivo cell kinetics before treatment by conventional radiation therapy. Thirty-seven tumors were analyzed by flow cytometry. Values of median potential doubling time (Tpot), labelling index (LI), and duration of S phase (Ts) were, respectively, 10.9 days, 3.8%, and 10.8 hours. In 35 cases, the results obtained from two biopsies of the same tumor were compared. A good reproducibility was obtained for LI and Tpot (P < 0.01). Thirty-one tumors were analysed by immunohistochemistry and labelling index (HLI) was determined in 24 tumors with a percentage of labelled cells varying from 6.1% to 39.2% (median value = 18.5%). No correlation was found between LI and HLI, but when observations were focused on the restricted group of DNA aneuploid samples, mean values of LI and HLI were closer (respectively, 12.8 +/- 4.5% and 18.3 +/- 7.7%) and a good correlation was obtained (P = 0.01). Moreover, no difference in proliferation was found between diploid and aneuploid tumors. Considering these results, a combined Tpot was calculated that allowed classification of tumors as highly or slowly proliferative.