The objective of this paper is to give conditions ensuring that the backward
partial integro differential equation (PIDE) arising from a multidimensional
jump-diffusion with a pure jump component has a classical solution, that is the
solution is continuous, $\mathcal C^2$ in the diffusion component and
$\mathcal{C}^1$ in time. Our proof uses a probabilistic arguments and extends
the results of Pham (1998) to the case where the diffusion operator is not
elliptic in all components and where the jump intensity is modulated by a
diffusion process.