  Angiogenesis is a key process in the tumoral growth which allows the
cancerous tissue to impact on its vasculature in order to improve the
nutrient's supply and the metastatic process. In this paper, we introduce a
model for the density of metastasis which takes into account for this feature.
It is a two dimensional structured equation with a vanishing velocity field and
a source term on the boundary. We present here the mathematical analysis of the
model, namely the well-posedness of the equation and the asymptotic behavior of
the solutions, whose natural regularity led us to investigate some basic
properties of the space $\Wd(\Om)=\{V\in L^1;\;\div(GV)\in L^1\}$, where $G$ is
the velocity field of the equation.
