The growth of a cancer is dependent on several factors:
- The time it takes for a cell to duplicate itself (the cell cycle time Tc)
- The percentage of cells within the tumour that are growing (the growth fraction GF)
- The number of cells from the tumour that are lost, either through cell death or senescence (the cell loss factor)
The potential doubling time Tpot of a tumour is the time it would take for a tumour to double in size, assuming that no cells are lost. It is found by:(1)
The volume doubling time VDT is the observed time a tumour takes to double in size.
The cell loss factor CLF relates the potential doubling time to the volume doubling time, and is found by:(2)
The CLF for many tumours is over 80-90% once they have reached a significant size.
Factors influencing tumour kinetics
Tumours are thought to grow rapidly at first due to a low cell loss factor - the tumour is small enough that poor vascular supply and central necrosis are less of a problem. A tumour cell must undergo thirty divisions to form a clinically detectable mass.