We study noncompact surfaces evolving by mean curvature flow. Without any
symmetry assumptions, we prove that any solution that is $C^3$-close at some
time to a standard neck will develop a neckpinch singularity in finite time,
will become asymptotically rotationally symmetric in a space-time neighborhood
of its singular set, and will have a unique tangent flow.Comment: More references added, typos correcte

Gang, Zhou