I'm wondering what effect will you have if you received blood from a pre-cancerous donor?

You will never know: We all are at some stage of "pre-cancerous-ness." with the strict guidelines in place for blood product usage in the us due to its limited availability, the potential risk you ask about is far outweighed by the therapeutic benefit of the transfusion. Donors must be generally healthy and blood is tested, so would be very very early and not likely in blood from a starting solid tumor.