E33 Tumor mechanics

Topic

When a tumor grows within a confined space, that growth generates mechanical forces that would not exist if the tumor could expand freely.

These mechanical forces are of three types: growth pressure, which builds up within the tumor itself as its cells multiply without room to expand; interstitial fluid pressure, which is the pressure of the liquid filling the spaces between the tumor cells; and elastic deformations imposed by the tumor's growth on the surrounding tissue.

These mechanical forces have direct biological consequences: they compress the blood vessels running through or around the tumor, causing hypoxia; they collapse lymphatic vessels, which in turn further increases interstitial fluid pressure; they generate mechanosensitive signals that tumor cells interpret and use to modulate their proliferation; and they prevent drugs from penetrating the tumor.

The physics underlying these mechanical forces is continuum mechanics applied to biological tissues: the tumor behaves neither as a liquid nor as a pure solid, but rather as a viscoelastic material that accumulates internal tensions—residual stress—as it grows.

This residual stress remains hidden while the tumor is confined within the body but is released as soon as the tumor is excised; upon cutting, the tumor tissue expands, and the extent of this expansion is precisely what allows for the quantification of the growth pressure that had accumulated within the tumor while it was growing under confinement.

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