I will be evaluating the anti-cancer activity of several crude extracts on breast cancer cells using the MTT assay. My question is, should the serum content of the media be reduced when i treat the wells with my extract? I have come across lab members who reduce the serum content of their wells during treatment while others keep it at 10% supplemented media. Any feedback would be most welcomed

My proposed protocol is as follows:
Day 1
Seed cells at 6000 cells /well suspended in 10% supplemented media in 69 well plates.
Day 2
add extracts at concentrations of 0, 15, 25, 50, 75, 100 microgram/ml
* Should serum free media be used here? or maintain at 10% supplemented media?
incubate for 72 hours.
Day 4.
add MTT, incubate for 4 hours, dissolve formazan with DMSO and read plate at 570nm.