Figure 1. Cancer cell proliferation is markedly suppressed by the standard cell culture conditions used for in vitro experiments.

Equal numbers of A2780 ovarian cancer cells were seeded in a 10 cm petri dish and were routinely maintained under 3% O₂ (physiological) or 21% O₂ (ambient). The increase in cell numbers was determined by counting manually once in three days, and the total cell numbers were estimated and plotted using linear scale (in Graph A) and log scale (in Graph B).