Why does chemotherapy stop some tumors from growing, but not others?

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Hey y’all.

My dad was diagnosed with stage four non-small cell lung cancer back in February. It’s been a tough few months. He had three rounds of chemo and then they did a follow-up scan last week. They told us that he had a mixed reaction to the chemo. While it seemed to shrink the tumors that were initially giving him pain (yay less pain!), it seems some smaller tumors appeared/grew a little bit (between 0.3 to 0.5 centimeters, not yay).

Can anyone explain to me in simple terms why this occurs, or direct me to online resource to explain why that occurs? Why chemotherapy shrinks some tumors but not others/doesn’t keep it from spreading?

Thank you.

In: Biology

3 Answers

Anonymous 0 Comments

Think about cancer the same way you might think about a bacterial infection. The cancer is kind of it’s own organism, and can mutate seperately from the human it’s infecting. The ability to mutate quickly is what makes cancer, cancer.

When you go through chemo, you’re using a specific drug or cocktail of drugs with a specific mechanism. Some of those cancerous cells are going to either A. Be innately resistant to that drug or B. Develop resistance to that drug.

As an example, docetaxel is a common chemo drug. It works by binding to something called tubulin, which is the protein that acts as a scaffold inside cells. It’s really important that tubulin is able to break down and move around if the cell wants to divide. Docetaxel glues all the tubulin together.

A cancer can develop docetaxel resistance in a few ways.

* Mutations that change the site on the tubulin where docetaxel binds, so it can’t any more.
* Mutations in things that depend on tubulin such that they can work without it
* Increased amounts of cellular pumps that can spit out docetaxel from the cell

Lots of other drugs follow that same sort of pattern – either change the target of the drug, change the cell’s mechanisms around the target, or just do some things so the drug can’t get in, or gets spat out.

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