A spike in U.S. demand for flu drug Tamiflu and strong sales of mainstay cancer medicines lifted first-quarter sales at Roche by a bigger-than-expected 5%.

The healthy performance in its main pharmaceuticals unit - which was also bolstered by approval of two new breast cancer drugs - offset weak sales in diagnostics, and the Swiss group confirmed its forecast of rising sales and profit for 2013.

The world's largest maker of cancer drugs said quarterly sales rose to 11.59 billion Swiss francs ($12.44 billion), compared with the average analyst forecast of 11.45 billion francs in a Reuters poll.

Sales in the smaller diagnostics business were up just 1% in the quarter with diabetes care down 5%, due to stiff competition and pricing pressure.

Demand for Tamiflu - a smaller seller than Roche's cancer blockbusters - accounted for half the beat in the pharma division, with sales surging 84% in the quarter following a severe flu season in the United States.

Chief Executive Severin Schwan said the bumper Tamiflu sales would not last and demand had already tapered off since the end of February. But he was "confident" of meeting the company's full-year targets.

"The Roche group is off to a good start in 2013," he told reporters in a conference call on Thursday, adding that the company would continue to look for bolt-on acquisitions of interesting products and technologies.

Roche, which does not detail quarterly profits, is the first company to report among major drugmakers this quarter.

Biotech drugs

Roche's drugs business has so far been spared the pain from a wave of patent expiries ravaging rivals, as most of its top-selling medicines are biotech drugs consisting of proteins derived from living organisms which are difficult to copy.

The Basel-based firm expects full-year sales to grow in line with 2012 when they rose 7%, and core earnings to rise ahead of revenues. It said it expected to further increase its dividend in 2013.

Some analysts have said Roche's guidance is conservative and expect the advent of new expensive cancer drugs as well as the company's pledge to keep a lid on research spending to drive double-digit core earnings this year.

Although its top-selling blood cancer drug Rituxan goes off patent in Europe at the end of this year, sales are expected to hold up as Roche does not anticipate competition from lower-cost copies known as "biosimilars" until early 2016.

Sales of Rituxan, which is sold as MabThera in Europe, rose 6% at constant exchange rates to 1.70 billion francs in the first quarter, in line with analyst forecasts.

Sales of another big cancer drug, Avastin, rose 11% to 1.53 billion francs, better than expected, as a result of increased use in both ovarian cancer and colorectal cancer.

Roche hopes follow-on drugs will help extend the shelf life of its current best-sellers, which also include breast cancer medicine Herceptin - a drug that it plans to use in combination with newer medicine Perjeta.

Perjeta, which won European approval last month after getting a nod from U.S. regulators last year, had sales of 50 million francs in the first quarter.

Roche also has high hopes for a novel chemotherapy-carrying "armed" antibody called Kadcyla, which clinched U.S. approval in February.

Investors are waiting for data due in early June on a compound known as GA101, which Roche is positioning as a follow-on to Rituxan.