Roche already has a 56-percent stake in Genentech and said it expects Genentech to appoint outside financial and legal advisers to help it evaluate the offer, The Wall Street Journal reported.

The deal would give Roche full control of one of the world's top biotech operations but goes against its longstanding policy of keeping subsidiaries at a distance. The offer represents a premium of 8.8 percent on Friday's closing price for Genentech shares.

The Financial Times reported Roche intends to allow Genentech autonomy over research and early development but will more closely integrate and share intellectual property -- something currently precluded by minority ownership.

Roche estimates the deal will save as much as $850 million a year.

Genentech refused comment.