  We consider a three-state model comprising tumor cells, effector cells and
tumor detecting cells under the influence of noises. It is demonstrated that
inevitable stochastic forces existing in all three cell species are able to
suppress tumor cell growth completely. Whereas the deterministic model does not
reveal a stable tumor-free state, the auto-correlated noise combined with
cross-correlation functions can either lead to tumor dormant states, tumor
progression as well as to an elimination of tumor cells. The auto-correlation
function exhibits a finite correlation time $\tau$ while the cross-correlation
functions shows a white noise behavior. The evolution of each of the three
kinds of cells leads to a multiplicative noise coupling. The model is
investigated by means of a multivariate Fokker-Planck equation for small
$\tau$. The different behavior of the system is above all determined by the
variation of the correlation time and the strength of the cross-correlation
between tumor and tumor detecting cells. The theoretical model is based on a
biological background discussed in detail and the results are tested using
realistic parameters from experimental observations.
