The European Commission has opened a formal antitrust investigation into South African manufacturer Aspen Pharma over concerns of excessive pricing of five cancer medicines.

The probe is the commission’s first investigation into excessive pricing practices in the pharmaceutical industry and will focus on five drugs Aspen acquired after patent expiration: chlorambucil, melphalan, mercaptopurine, tioguanine and busulfan, sold under different formulations and brand names.

The commission said it has information that Aspen threatened to withdraw the medicines from some countries in order to impose the price increases, and actually did withdraw products in some cases.

The investigation covers all of the European Economic Area except Italy, where the national competition authority fined Aspen in October 2016 for raising the price of four of the drugs by up to 1,500 percent.