The forward has featured in 11 Serie A games so far this season and he has scored three goals in that time.
He has made 58 appearances for the club signing joining from Genoa in 2016 and the Argentina international is hoping to fire the club to the Serie A title this season.
The 29-year-old scored the winner in the 1-0 win over Qarabag on Tuesday and he is now ready to kick on in Rome.
He told the club's official website: "To be honest, I’ve felt like an important part of this team ever since my first game against Sassuolo.
"I didn’t play so much in the last six months of last season, but I stuck at it. I’ve always played regularly in my career – sometimes I’ve done well and other times my performances haven’t been so good, but I’ve always given it everything I’ve got.
"Between the last game of last season and the start of this campaign, this has been one of the best spells of my career and I’m delighted to get this reward."