Walkathons, fundraisers, and ribbon-shaped bumper stickers raise research dollars and boost spirits, but cancer—the dreaded disease that affects more than 14 million people and their families at any given time—still remains bereft of a cure.

Why? For starters, cancer isn't just one disease—it's more than 100 of them, with different causes. This makes it impossible to treat each one using a one-size-fits-all method. Secondly, scientists use lab-grown cell lines cultivated from human tumors to develop cancer therapies. Living masses are far more complex, so potential treatments that show promise in lab experiments often don't work on cancer patients. As for the tumors themselves, they're prone to tiny genetic mutations, so just one growth might contain multiple types of cancer cells, and even unique sub-clones of tumors. These distinct entities might not respond the same way, or at all, to the same drug.

These are just a few of the challenges that cancer researchers face—but the good news is that they're working to beat all of them, as this TED-Ed video explains below.