  For a disordered two-dimensional model of a topological insulator (such as a
Kane-Mele model with disordered potential) with small coupling of spin
invariance breaking term (such as the Rashba coupling), it is proved that the
spin edge currents persist provided there is a spectral gap and the spin Chern
numbers are well-defined and non-trivial. These conditions on being in the
quantum spin Hall phase do not require time-reversal symmetry. The result
materializes the general philosophy that topological insulators are non-trivial
bulk systems with edge currents that are topologically protected against
Anderson localization.
