Figure 5. Karyotypic stability and drift of the tumorigenic clone cen3tel PD166 at the time of isolation (A) and after 451 (B) and 848 (C) unselected generations in vitro. As a test for immortalization, karyotype arrays prepared from the original clone cen3tel PD166 and descendents isolated 451 (PD617) and 848 (PD1014) unselected generations later were compared. These karyotype arrays show that the original cen3tel PD166 karyotype was mostly stable, but was also variable within narrow margins over 848 cell generations (Table 4). The copy numbers of 21 of 33 (64%) PD166-specific chromosomes including marker chromosomes were clone-specific during 848 generations, while 12 of 33 (36%) were generation-specific or cell-specific drifting within narrow margins of ± 1 over 848 generations (Table 4 and Fig. 6). Based on the high clonal stability over 848 unselected generations, we conclude that the cen3tel PD166 clone is immortal but flexible, exceeding the operational Hayflick threshold of 50 generations by 798 clonal generations.