The Eredivisie side are in the market for a new striker after top goalscorer Luuk de Jong joined Borussia Monchengladbach this summer, and have made the 19-year-old their top candidate.
The Enschede club have reportedly agreed personal terms with the former Feyenoord player and have also agreed a fee of around €7 million with Inter.
The player’s agent, Karim El Atmadi, revealed that the teenager rejected the opportunity to partner compatriot Ricky van Wolfswinkel at Sporting Lisbon in favour of a move to Twente.
"Luc would prefer to return to Netherlands," El Atmadi admitted. "Feyenoord were also in the race, but the club wanted to get him on loan, so they pulled out."Castaignos joined Inter from Feyenoord for €3 million in 2011. The Rotterdam side will receive five percent of the transfer fee as training compensation.