Eli5: Why is a cancer a lot worse when it happens a second time?

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Eli5: Why is a cancer a lot worse when it happens a second time?

In: Biology

The first time it can be localized to one or a cluster of tumors. The second means it was more wide spread and/or has become more wide spread than originally thought. You can have lots of little tumors which are harder to remove. Early detection is what you hope for.

It’s evolution on a very small scale!

Think about it like this: cancer is a bunch of cells basically going haywire and not following any rules. They’re constantly changing for the bad and for the good – while cancer cells can, for instance, multiply lots, they can have certain dependencies and sensitivities as well (these are targets for a lot of therapeutics!). The more unstable and mutated a cell is, the more likely other cell machinery isn’t working correctly putting the cell at high risk of a meltdown (apoptosis).

In a treatment-naive primary tumor, the population of cancer cells is pretty diverse. Other than the immune system, the cells haven’t had too much pressure on them, lots of them can get by and continue growing.

But when you treat, especially using chemotherapeutics or radiation, you’re causing mass cell death. Preferably, these treatments wipe out all cancer cells, or at least enough to prevent the residual cells from continuing on.

Unfortunately, we often struggle to eliminate enough of the cancer. While the unstable and highly mutated cells can be totally wiped out, populations of therapy resistance cells that were lucky enough to get a helpful mutation are then given the opportunity to grow into secondary disease. As a result, the same treatment won’t work nearly as well, if at all. Plus, these hypothetically therapy resistance populations may be more aggressive or metastatic than the inital heterogeneous population.

Please feel free to correct anything that’s wrong! I’m a PhD student studying cancer evolution and love this stuff