GENEVA (AP) â¿¿ Strong sales of new cancer drugs and a severe U.S. flu season helped lift Swiss drug maker Roche Holding AG's revenue by 6 percent in the first quarter. The world's biggest manufacturer of cancer drugs said Thursday that sales rose to 11.56 billion Swiss francs ($12.4 billion) during the first three months of the year, up from 11.03 billion francs in the same period last year. Severin Schwan, the chief executive of Basel, Switzerland-based pharmaceutical company, described it as "a very good start in 2013" and attributed much of the advance to an 84 percent increase in Tamiflu sales during the U.S. flu season. Also helping were two new cancer drugs that the company hopes will mirror the performance of its three top-selling cancer medicines MabThera/Rituxan, Herceptin and Avastin. "The launch of two new cancer drugs, Kadcyla in the United States and Perjeta in Europe, will help to further improve our leading market position in oncology," Schwan said in a statement. The company also said there was strong demand for its ovarian cancer drug Avastin in Europe. Roche, which reports its earnings only every six months, said group sales for 2013 are expected to grow in line with last year's 4 percent increase. Unlike many of its major competitors, the company benefits from having strong sellers whose patents are not expiring soon. But like many other major Swiss companies it has battled against the strength of the franc in recent years, a situation that somewhat reversed in 2012. Roche said the rise of the franc against the yen by 13 percent impacted its group sales in francs by 1 percent. Shares in Roche were trading up 0.2 percent Thursday morning at 226 francs on the Zurich exchange.