system
Given the following post, respond as if you're commenting on Reddit:
human
How is testicual cancer (or any cancer in less than vital organs like cervix, breasts etc.) potentially lethal?

Of course, I am going under the assumption that such a cancer will, untreated, ultimately lead to death. I am, however, not exactly sure how.

What I am thinking is that, as organs like the testicles, ovaries, and breasts are (seemingly) not vital to staying alive, it is not that cancer in itself that will cause death. Rather, it is the metastasis to vital organs (or several non-vital leading to increased stress, in some way) that will lead to complications in those organs.

Am I on the right track with this way of thinking? If not, why?
gpt
Look at something called Cancer Staging, it will give you some defined framework on how professionals look at things. Here is a quick way to look at it. Lets start with an abnormal breast cell that is the start of cancer. This cell reproduces over and over but due to the mutations in this cell the result is not other healthy breast tissue but rather cancer. Since it is not typical breast tissue when it replicates the cells do not stay put. The bad cells can branch out, they reproduce and follow pathways in the body. Things like the lymphatic become mechanisms for these cells to grow in other areas of the body. So now cells that started as just mutated breast tissue are growing and taking over areas like the lungs.