signal proteins are necessary for normal function of any cell in a multicellular system, and there are different types for different function, but I don't know how many there are either. Never needed to know that. It's odd that all cancers would share this one signal protein -- but shit, the proof is in the doing. It seems to be these researchers believe (and have some proof of) that the factors which lead to cancerous states also favor this particular protein expression. Exactly why that should happen is probably a matter of ongoing studies.
"Cure" seems a bit overstated. If that pans out it's an important step forward in reliable and effective treatment. It sounds like a way to include the innate immune function in chemo therapies. But, and maybe I'm just ignorant, it doesn't sound like a direct replacement for chemotherapy.
One thing that makes cancer cancer is that the immune system does not regulate the growth of the tissue. That failure is because of these signal proteins. So isolating which signal protein cancerous cells favor expressing is a good solid step.