Blood donor with Metastasized Cancer?

Curiosity prompts me to ask this question:

If someone had metastasized cancer, didn’t know it and gave blood,
why would cancerous cells in the blood not transfer to the blood recipient?

I know that in the case of leukemia, blood marrow produces the abnormal white blood cells, but for malignant tumors why can they not be transferred to another person’s blood stream?

Just want to know…

Typo,
I know in the case of leukemia [BONE] marrow produces the abnormal white blood cells.

If a person has Leukemia, the blood count tests done to screen the donation will be all out of whack. The blood will be discarded, and the donor notified, saying, “See your doctor immediately.”

Other blood tests are done as part of the screening process, and I would think the chemistries would be out of whack if a person is sick with a metastasizing cancer. I do know that liver enzymes are checked, because a friend was the recipient of the “See your doctor immediately, and you can’t donate blood any more” phone call.

If, perchance, none of the screening tests are indicative of something wrong, I would suppose the recipient’s own immune system would attack and kill the cancerous cells. In fact, it’s theorized that a cancer patient’s OWN immune system is faulty when it permits the cancer to grow.

IANAD, but this is information I’ve accumulated over the eons.
~VOW