  We consider a hyperbolic-parabolic system arising from a chemotaxis model in
angiogenesis, which is described by a Keller-Segel equation with singular
sensitivity. It is known to allow viscous shocks (so-called traveling waves).
We introduce a relative entropy of the system, which can capture how close a
solution at a given time is to a given shock wave in almost $L^2$-sense. When
the shock strength is small enough, we show the functional is non-increasing in
time for any large initial perturbation. The contraction property holds
independently of the strength of the diffusion.
