Gompertzian tumour growth

The Gompertz function describes growth whose rate falls exponentially with size, so a tumour grows fastest when small and approaches a plateau as it outstrips its blood supply. Laird showed in 1964 that it fitted animal and human tumours far better than exponential growth, and it became the basis of Norton and Simon's reasoning about dose density, of models of micrometastatic disease after surgery, and of estimates of how long a tumour has been present at diagnosis. Its parameters are hard to measure in a single patient, and other sigmoidal laws (logistic, von Bertalanffy) fit many series equally well.