The cytochrome P450 family 19 subfamily A member 1 (CYP19A1) gene, encodes aromatase, a key enzyme in estradiol (E2) synthesis, and is down-regulated during porcine follicular atresia. CYP19A1 gene stimulates E2 release and inhibits cell apoptosis in porcine granulosa cells (GCs). The single nucleotide polymorphisms in CYP19A1 gene may alter aromatase activity and circulating steroid hormone levels in females. High CYP19A1 expression was highly significantly associated with a poor overall, disease-free, and metastasis-free survival in estrogen receptor-positive but not negative breast cancer patients. Estrogen production by the human villous trophoblast is dependent on the biosynthetic enzyme aromatase (CYP19; CYP19A1) and is crucial for successful placental development and pregnancy outcome.