In this talk, we review the recent developments of the next-to-next-to leading order contribution to
the $\mu e$-elastic scattering. We focus our discussion on the interference between the
two-loop and the Born amplitude. In particular, we discuss the analytic reduction of the two-loop amplitude
by means of the integrand reduction methods and the application of the integration-by-parts identities.
On top of it, we show preliminary results for the ultraviolet renormalisation of the latter.