Roche Holding AG is bracing for slower earnings growth this year as its ageing cancer blockbusters face competition and the Swiss drugmaker readies a new generation of medicines. The world’s biggest maker of cancer drugs is pushing out new treatments such as the cancer immune therapy Tecentriq to buoy earnings as it faces the prospect of biosimilar competition for its top sellers Rituxan, Herceptin and Avastin, targeted tumor therapies that were revolutionary when they were first approved in the late 1990s and mid-2000s.