WASHINGTON Every year, the editors of Science huddle together and pick an outstanding scientific achievement as the Breakthrough of the Year. This year's winner is:

CANCER IMMUNOTHERAPY: harnessing the immune system to battle tumors.

Scientists have thought for decades that such an approach to cancer therapy should be possible, but it has been incredibly difficult to make it work. Now many oncologists say we have turned a corner, because two different techniques are helping a subset of patients. One involves antibodies that release a brake on T cells, giving them the power to tackle tumors. Another involves genetically modifying an individual's T cells outside the body so that they are better able to target cancer, and then re-infusing them so they can do just that.

We are still at the beginning of this story and have a long way to go. Only a very small proportion of cancer patients have received these therapies, and many are not helped by them. Doctors and scientists still have a lot to learn about why the treatments do and do not work. But the results have been repeated at different centers and in different tumor types, giving doctors hope that immunotherapy for cancer may benefit more and more people in the future

The editors also singled out nine runners-up for special praise:

GENETIC MICROSURGERY

A year-old gene-editing technique called CRISPR touched off an explosion of research in 2013. It's short for "clustered regularly interspaced short palindromic repeats": repetitive stretches of DNA that bacteria have evolved to combat predatory viruses by slicing up the viral genomes. The "knife" is a protein called Cas9; in 2012, researchers showed they could use it as a scalpel to perform microsurgery on genes. This year the new technology became red hot, as more than a dozen teams wielded it to manipulate specific genes in mice, rats, bacteria, yeast, zebrafish, nematodes, fruit flies, plants and human cells, paving the way for understanding how these genes function and possibly harnessing them to improve health.

CLARITY BRAIN IMAGING

This year, researchers invented a new way of imaging the brain which many say will fundamentally change the way labs study the intricate organ. CLARITY, a method of rendering brain tissue transparent, removes the biggest obstacle to traditional brain imaging: the fatty, light-scattering molecules, called lipids, which form cellular membranes. By replacing lipids with single molecules of a clear gel, the technique renders brain tissue transparent while leaving all neurons, other brain cells and their organelles intact. This allows researchers to infiltrate the brain with labels for specific cell types, neurotransmitters, or proteins, wash them out, and image the brain again with different labels - a process they say could speed up by a hundredfold tasks such as counting all the neurons in a given brain region.

CLONING HUMAN STEM CELLS

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Science's top 10 breakthroughs of 2013