Since these investigators realized very early in their studies the importance of aromatase enzyme activity on breast, ovarian, and endometrial cancers and the mechanism of gynecomastia, soon many studies examined (1) how via mechanistic biochemical (step-by-step) processes estrogen biosynthesis took place, (2) where aromatization occurred in the body, (3) much more importantly how to regulate or inhibit the aromatase enzyme, and, finally, (4) what was the molecular biology structure of aromatase and its tissue-specific expression and regulation. Here, CYP19A1 is linked to Gynecomastia.