  A small portion of a tissue defines a microstate in gene expression space.
Mutations, epigenetic events or external factors cause microstate displacements
which are modeled by combining small independent gene expression variations and
large Levy jumps, resulting from the collective variations of a set of genes.
The risk of cancer in a tissue is estimated as the microstate probability to
transit from the normal to the tumor region in gene expression space. The
formula coming from the contribution of large Levy jumps seems to provide a
qualitatively correct description of the lifetime risk of cancer, and reveals
an interesting connection between the risk and the way the tissue is protected
against infections.
