Roche aims to combine Perjeta with its older drug Herceptin, the company's second-biggest seller, for women with a form of cancer known as HER2-positive, which makes up about a quarter of all breast cancers and has no cure.
U.S. health regulators approved the drug last June and Perjeta won initial backing from European authorities in December.
Perjeta, part of Roche's strategy to develop new drugs to extend the longevity of its best-selling brands, had sales of 56 million Swiss francs ($59 million) in 2012.
Analysts forecast peak sales of roughly 2 billion francs.
Breast cancer is the most common cancer among women, with about 1.4 million new cases diagnosed each year and more than 450,000 women dying of the disease annually, according to the World Health Organization.
A typical 18-month course of Perjeta plus Herceptin costs approximately $188,000.
Roche is also developing an "armed antibody" known as TDM-1 as a treatment for HER2-positive breast cancer. TDM-1 combines Herceptin with a derivative of a powerful type of chemotherapy and is designed to reduce unpleasant side effects. ($1 = 0.9417 Swiss francs)
(Reporting By Katharina Bart, editing by Emma Thomasson and David Cowell)