The Swiss firm said on Friday Richard Scheller, 61, had decided to retire as head of Genentech Research and Early Development -- known as gRED -- on Dec. 31. Michael D. Varney, who currently leads the company's small molecule drug discovery unit, will take over as head of gRED and become a member of the enlarged corporate executive committee. Scheller is the latest high-profile departure from Genentech, seen as the main driver of the company's drugs pipeline having produced Roche's three top-selling medicines since 2011 as well as new breast cancer drugs Perjeta and Kadcyla.