how does cancer return back more aggresively after treatment?
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Treatment can kill the weakest cancer cells. If you don’t get them all, then you are left with the strongest aggressive cells.
It’s not so much aggressive as less inhibited.
For any given tumor type, there are bio markers associated with the tumor that serve as either indicators of treatment response or targets for killing the cancer cells. For example, non-small cell lung cancer (NSCLC) may be labeled as ROS1+ or ALK+, either of which may require different treatment.
Now, if we are using a treatment that specifically hits marker A, we may see tumor shrinkage or remission. But, what if some of marker A is left and allowed to reestablish. Marker A is probably going to develop some resistance to that compound, meaning further use of that drug will either be less effective, require a different drug, or require an added drug.
Then, we run into the issues of adding drugs! More drugs is going to have a heightened effect in the body, and coupled with the already abnormal environment with the cancer, it leads to furthering sickness.
In cancer research, we don’t see a lot of studies trying to improve on a drug’s efficacy. Most of them are trying to get close to existing drug’s efficacy with a goal of minimizing adverse events (safety before efficacy).
As Nietzsche said:
>What ever doesn’t kill you makes you stronger.
That’s the best ELI5 I can do. To be specific, it can come back stronger bc the cells have adapted to be resistant to therapy. Also, bc the cells which have survived are the more transient (malignant) cells which are already spreading vs the cells which are proliferating in one specific organ.
You’ve killed the weaker cancer cells and the ones that remained were the strong ones. It’s like antibiotic resistant bacteria, except instead of bacteria being selected by the antibiotic, it’s a population of cancer cells being selected by the treatment.
Also the next time it comes back your immune system is probably weaker as a result of the cancer treatment itself.
It doesn’t always, even if it comes back, but it can.
The best answer I see here is from u/LogSouth2717.
Basically, a few things. We may have treated the cancer almost perfectly, but not quite, according to type. There are SO many types, grades, stages, locations, etc. As he said about NSCLC, doctors can select just barely the wrong type, or insufficient treatment and kill all but the worst little tiny bit of the tumors.
Next, some tumors do develop resistance to drug therapies, if they don’t get the whole thing the first time.
Also, remove a tumor and do the chemo, and hope you got all the “seeds”. If you didn’t, they will pop back up rapidly, and at the same time.
Whatever genetic or evironmental factors lead to the tumors are still there, and cancer treatments themselves can be pretty hard on the body, leaving you less resilient against the next one. It’s common for people to develop a new disease after being treated for the first.
u/LogSouth2717 had a good explanation, which I understood as:
It’s not necessary the cancer that is returning more aggressive, it just appears that it’s more aggressive bc the body had been wrecked by the initial treatment against the first wave. So when the second wave of cancer hits, your body is significantly weaker and can’t fight it as well as the first time around
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