Implications of tumor growth rate for the natural history of lung cancer.

The growth rate of lung cancer may be described by an exponential model in which the volume doubling time, or growth rate, is constant. The doubling time may vary from case to case by an order of magnitude so it is probably the most important factor in the natural history of the disease. While some aspects are uncertain, the exponential model seems to be reasonably valid because it is coherent with what we already know about the course of the disease. It helps explain the long interval between onset of carcinogen exposure and clinical manifestation, the reversibility of risk after cessation of smoking, the results of periodic roentgenographic screening, and the variability of prognosis. As a result, the exponential model has certain medicolegal implications.