E21 Tumor growth

Topic

The number of tumor cells changes over time based on the interplay of two factors: the net proliferation rate of each individual cell—determined by cell cycle behavior—and the constraints imposed on the tumor by its own microenvironment, such as nutrient availability, available physical space, and mechanical pressure exerted by neighboring cells.

Furthermore, the tumor cell count within this model serves as a bridge between two distinct scales: the cellular scale, which addresses when a single cell divides, and the clinical scale, which addresses questions such as when the tumor cell count becomes detectable or when symptoms begin to manifest in the patient.

The physics governing changes in the tumor cell count over time is described by population dynamics, a process that shifts through different regimes as the tumor grows. Initially, when the tumor consists of few cells and the microenvironment imposes no significant constraints, the tumor cell count grows exponentially—with each cell continuing to divide at a constant rate, unimpeded.

As the tumor continues to grow, competition for resources within the microenvironment begins to limit expansion, causing the growth pattern to shift from pure exponential to logistic. Later, during the tumor's clinical phase, the growth of the tumor cell count is best described empirically by the Gompertz model.

Each of these three regimes—pure exponential growth, logistic growth, and the Gompertz model—corresponds to a different stage in the tumor's life cycle, and each carries distinct implications for the patient's prognosis and the tumor cell count's response to treatment.

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