Dakshat makes a good point. We won’t overcome it until we fully understand it.
I seem to remember hearing that cancer is kind of inevitble though, as every time your DNA replicates, small bits fall off and it makes a non-perfect copy, which makes forming a cncerous cell more likely. This may be more of an explanation for ageing than cancer, so take that with a pinch of salt!
(Dakshat is also the guy to go to about ageing!)
Like Dakshat and Lewis said, cancer will never be fully cured until we understand it. However, we have made a lot of progress in managing many forms of cancer. For many cancers, people often now live happily and relatively healthily long after their diagnosis. Some of this success is because of new treatments, but early testing and diagnosis also means that treatment is more successful. The more we understand about cancer, the more we can detect it early (before it spreads) and the more easily we can stop it from growing.