The KO of NAT1 activity by both gRNA #2 and gRNA #5 in MDA-MB-231 breast cancer cells caused a modest but significant (p < 0.0001) elevation in doubling time but neither gRNA #2 or gRNA #5 caused significant (p > 0.05) elevation in doubling time for the MCF-7 breast cancer cell line. The gene discussed is NAT1; the disease is breast cancer.