Is preventative chemotherapy a thing?

Three weeks ago I had a big old germ-cell tumor removed from my chest, it was kind of sitting on top of my diaphragm in a lymph node. There were a couple of other nodes removed cause they were growing too. This caused my doctor concern of potential lymphoma or downstairs cancer or whatever. The labs came back as a germ cell tumor and no more mentioning of cancer. On Tuesday I had my two week exam, and yesterday they did some more tests on me: I had a scrotal sonogram, and a CT scan on my stomach and lower body and just a regular chest xray. The results of this new imaging has not come back yet.

Anyway my doctor has never said the word cancer other than the initial concern before the original labs came back, and in the medical records I have access to the word hasn't been said. The info I have is that it was a non-cancerous germ-cell tumor that likely is from some cells that didn't fully migrate when I was an embryo. But My doc has still recommended chemo and referred me to a chemo therapist.

I understand being safe: If there is something there we haven't seen lets kill it. I'm wondering if preventative/pre-cancer chemo is common?

Edit: Imaging results came back and maybe I do have some cancer or something: Scrotal Exam came back with terminology Mildly heterogeneous, hypoechoic macrolobulated mass or adjacent masses within the left testis consistent with primary testicular neoplasm. While there are many features suggesting seminoma, cannot exclude component of a mixed germ cell neoplasm. And CT came back with There is a enlarged left para-aortic lymph node suspicious for malignant adenopathy.

Unfortunantly I'm just grabbing these results from my online portal thing and can't actually talk to my dr about it until monday which blows. Wanna find out if he thinks imma die soon