GameStop Corp. GME, +2.93% said Tuesday it has named Daniel DeMatteo as interim chief executive, replacing J. Paul Raines, who is seeking medical treatment after a reoccurrence of a previously disclosed illness. Raines had a cancerous tumor removed from his brain in 2014. DeMatteo, a co-founder of the company, has previously served as CEO and in other executive roles. Shares were flat premarket, but are down 36% in 2017, while the S&P 500 SPX, -1.11% has gained 15%.