Conflict of interest: V. Cottin reports receiving the following, outside the submitted work: personal fees and non-financial support from Actelion, Boehringer Ingelheim and Roche for consultancy, lectures and travel to meetings; grants to his institution from Boehringer Ingelheim and Roche; personal fees from Bayer/MSD and GSK for consultancy; personal fees from Gilead for acting as a member of an adjudication committee; personal fees from Novartis for consultancy and lectures; a grant from Sanofi for acting as a trial investigator; personal fees from Promedior for acting as the Chair of the DSMB; personal fees from Celgene for the DSMB; and personal fees from Galapagos for consultancy.