What is Formestane???

This is one of the things brian batchledor recommends in his 2week on 4off cycle but what the hell is it? and if i cant get it what can i use in place of it?

Formestane is 4-hydroxyandrostenedione which is a potent
and non-selective anti-aromatase use to treat hormone
sensitive breast cancer. It will prevent testosterone
from aromatizing. It’s a shitty drug, Arimidex (anastrazole) is much better and has replaced Formestane
in the United States for all intents and purposes.

–Brock