Figure 2: Reprehensive aromatase inhibitors: the first (1), second (2), and the third-generation aromatase inhibitors (3). Among the listed aromatase inhibitors, formestane and exemestane (circled) are irreversible steroidal aromatase inhibitors (Steroidal inactivators), whereas the others are nonsteroidal reversible aromatase inhibitors (Non-steroidal inhibitor).