system
Given the following post, respond as if you're commenting on Reddit:
human
When fighting testicle cancer, why is it that testicle 
is initially removed and then chemo is applied, not 
the reverse?

I understand that chemotherapy is highly effective in neutralising testicle cancer metastases. But if it kills cancer cells of this type, wouldn't it be logical to expect chemo to kill testicle cancer itself as well? So you start with chemo and then if there's anything left of cancer in the testicle, cut the testicle. But somehow that's not how it's traditionally done. Why?
gpt
The main reason is that surgery is an extremely targeted therapy whereas chemo is systematic and has many adverse affects on the rest of the body.  Let's say you wanted to treat testicular cancer without doing surgery first - the number of cancer cells in the body is higher, and the dose of chemo must be increased.  This increases side effects, which for chemo are quite significant.

Another secondary reason is that surgery is more effective than chemo on a solid tumor.  Chemo is carried by the blood, and so it can only work on tissue that is supplied by blood.  In tumors, the vasculature is malformed, leading to many parts of the tumor that don't receive blood directly.  They can get oxygen through diffusion through tissue, but chemo can't always reach these cells. But by cutting the entire tumor mass out of the body through surgery, these cells are removed.

edit: These are more general reasons comparing surgery to chemo.  The other posters have brought up many excellent points that are specific to testicular cancer.