ESR1 and breast cancer: Very interestingly, it has been demonstrated that cyclooxygenase (COX)-2-derived PGE(2) stimulates a transduction pathway contributing to enhance expression of aromatase (the rate-limiting enzyme for estrogen biosynthesis), and elevated progesterone receptor (PgR) levels in breast tissues from overweight and obese women.28 This deciphered pathway may contribute to initiation, progression as well as resistance to anti-aromatase therapies of ER + breast cancers in overweight and obese patients.