I have read that ADT limits cancer growth -- but does ADT by itself cause cancer death? Or only when combined with other treatments like radiation?

Some cancer cells die, some become dormant and do not progress any more and some are already resistant and continue to grow. Further, some cancer cells escape the ADT treatment by mutating to resistant cells.

Using imaging you can see that cancer lesions may shrink up to 30% in size after the start of ADT.

If you Google "lupron", you will find this:

"Is Lupron considered a chemotherapy drug?

Lupron® is an “antineoplastic agent”, meaning that it is a cancer chemotherapy drug. Like all antineoplastics, Lupron® is harmful to both cancerous and non-cancerous cells — particularly to pregnant women and developing fetuses."

I am informed that leuprolide chemo on its own does not kill cancer cells, however, it does prevent hormonally sensitive PCa cancer cells from dividing or moving. Since a typical PCa cell lives about 2 & 1/2 years, the hope is that surgery gets most of the cancer, radiation weakens/damages the remaining cells and - since they cannot divide or leave the area - they then die in place and you are cured.

Works, sometimes.