> Is it that extraordinary evidence needs to be provided for the claim that a poison (chemotherapy) is a cure for cancer?
Let's start by not conflating all kinds of cancer and all kinds of chemotherapy, because it's not a single disease, and the outcomes vary greatly.
But, for instance, survival rates for testicular cancer have risen significantly (or even dramatically) since the invention and introduction of the chemotherapy treatment that is being used for it today. If detection isn't overly delayed, the cure rate in the developed world today is around 95 to 100 percent.
So let's please, please, please, not go for cheap "chemotherapy = poison" rhetoric. I have first-hand experience with the adverse effects, but you can't dismiss a nearly 100% cure rate.
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Regarding what you more generally wrote, it's true that financial interests affect and direct the pharma industry. There are several adverse effects from that, such as research not being directed at areas with potential health benefits but low profitability, and also over-marketing (and thus possibly over-prescription) in other areas. It would also be great if medical research were less tightly bound to funding from the industry and rather got its funding from public sources instead. (That wouldn't make it non-politicized, but direct financial interests might not be as significantly involved.)
But it would be rather misguided to think that there aren't actual working treatments coming out of the industry and research as well. Sometimes those treatments are the difference between life and death. Let's not discount that.
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The significantly improved survival rates for TC are pretty well-known, but a couple of sources:
https://en.wikipedia.org/wiki/Testicular_cancer#Prognosis
https://jamanetwork.com/journals/jama/fullarticle/181433
https://ascopubs.org/doi/full/10.1200/JCO.2014.56.0896
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