[{"from": "human", "value": "Provide a description of this molecule. [C][=C][C][=Branch1][Branch2][=C][C][=C][Ring1][=Branch1][C][#N][C][Branch1][=N][C][=C][C][=C][Branch1][Branch1][C][=C][Ring1][=Branch1][C][#N][N][C][=N][C][=N][Ring1][Branch1]"}, {"from": "gpt", "value": "The molecule is an oral non-steroidal type II aromatase inhibitor first described in the literature in 1990. It is a third generation aromatase inhibitor like [exemestane] and [anastrozole], meaning it does not significantly affect cortisol, aldosterone, and thyroxine.  Letrozole was granted FDA approval on 25 July 1997."}]