Swiss drugmaker Roche has no plans to change its holding in Japan's Chugai Pharmaceutical and the recent weakening of the yen would not be a reason to trigger such a move.

Asked if Roche might raise its stake in Chugai, Roche CEO Severin Schwan told analysts on Thursday: "We don't see changes in the structural set-up ... currency fluctuations would not drive such strategic M&A decisions."

Chugai became a subsidiary of Roche in 2002 and the Swiss group currently owns 59.9% of the company. There has been speculation that Roche might look to take complete ownership of Chugai, as it did with the buyout of U.S. biotech group Genentech in 2009.

Schwan, however, said the situation with Chugai was "very different", adding there was a different arrangement of contracts between the two companies and Roche had already restructured its operations in Japan to remove duplication.

Roche paid $47 billion to buy the portion of Genentech it did not already own four years ago and since then has repaid 66% of the debt related to the deal.

Chugai is a significantly smaller business, with a total market capitalization of around $13.5 billion.

Roche earlier reported a 5% rise in first-quarter sales, driven by strong demand for its cancer drugs and a spike in revenue from flu drug Tamiflu due to a severe U.S. flu season.