The A_2 theorem, proven by T. Hytönen, establishes a long-standing conjecture on optimal weighted norm estimates of Calderón-Zygmund operators. We shall discuss how this result can be extended to singular integral operators whose kernel does not satisfy any regularity estimate. Examples of such operators are Riesz transforms and multipliers on Riemannian manifolds, or operators associated with a second order elliptic operator. The proof is based on a domination by adapted sparse operators. This is joint work with F. Bernicot and S. Petermichl.