Roche's efforts to produce successful non-cancer drugs from its own labs have been mixed, with setbacks in recent years for experimental drugs against heart disease, diabetes and schizophrenia.
The Swiss drugmaker already markets Pulmozyme for cystic fibrosis and Xolair for severe asthma in the United States and has other experimental respiratory products in clinical development, including another severe asthma drug called lebrikizumab.
The InterMune deal brings it a promising new drug, pirfenidone, for treating a progressive and ultimately fatal scarring condition of the lungs. Pirfenidone is approved for so-called idiopathic pulmonary fibrosis (IPF) in Europe and Canada, and is undergoing U.S. regulatory review.
Roche said on Sunday it would pay $74.00 a share through a tender offer for InterMune, representing a premium of 38 percent to the closing price on Aug. 22 and a 63 percent premium over Aug. 12 when takeover speculation around the stock began to circulate.]
The acquisition, which has been recommended by the boards of both companies, is the largest by Roche since 2009, when it bought out the remaining stake it did not already own in U.S. group Genentech for around $47 billion.
Analysts described InterMune's price tag as "hefty" given it only has one marketed product in a field that is likely to become increasingly competitive over time.
But Sanford C. Bernstein analyst Tim Anderson, who rates the stock 'outperform,' praised the decision to beef up outside oncology as a "smart tactical move."
Industry analysts expect pirfenidone, which is given as a pill, to have sales of $1.04 billion in 2019, according to consensus forecasts compiled by Thomson Reuters Pharma.
Shares in Roche were up 0.5 percent at 267.2 Swiss francs by 0806 GMT on Monday.
The large premium ascribed to InterMune is not unusual in biotech takeovers, reflecting intense competition for promising new drugs among larger companies, which rely on small innovative firms for a growing proportion of their products.
Roche said the transaction was expected to be neutral for its core earnings per share in 2015 but would boost profits from 2016 onwards. It said guidance for this year remained unchanged.
Chief Executive Severin Schwan said he believed there was a good strategic and cultural fit between Roche and the California-based biotech firm, and that it would continue to pursue "targeted" bolt-on acquisitions.
Roche generates a large amount of cash, leading to persistent speculation about deals. Its track record since Genentech has been for a series of small-scale purchases. It notably backed away from a $7 billion pursuit of gene sequencing firm Illumina Inc two years ago.
Roche may be accelerating efforts to bolster its presence in the treatment of rare diseases. Speculation last year linked Roche to Alexion Pharmaceuticals Inc and BioMarin Pharmaceuticals Inc.
There has been talk that Roche may buy the shares in Japan's Chugai Pharmaceutical Co Ltd that it does not already own for about $10 billion, although Chugai has denied it was in talks over a such a deal.
Schwan declined to comment on whether the InterMune deal would make a buyout of Chugai less likely.
Even after swallowing InterMune, Roche would still have the leverage to "very easily" buy out the rest of Chugai and do something else, said Kepler Cheuvreux analyst Fabian Wenner. But he conceded such a move may now be "somewhat less likely".
On Monday, shares in Chugai fell 9 percent after Bloomberg reported that Roche had decided against a buyout.
InterMune had considered selling itself about three years ago but decided not to pursue a deal at that time due to uncertainty over clinical data for pirfenidone, people familiar with the matter told Reuters previously.
Roche said its interest in a deal was triggered following positive late-stage trial results for the drug in May. The medicine also received a "breakthrough therapy" designation from the U.S. Food and Drug Administration (FDA). The term is reserved for drugs for serious diseases that appear to offer a substantial advance on existing therapies.
The FDA is due to give is verdict on whether to approve pirfenidone by Nov. 23 and Roche said it expected to launch the drug in the United States this year.
Healthcare companies are merging at a record pace, with year-to-date activity topping $346 billion, compared to $212 billion in the year-ago period, Thomson Reuters data showed.
Recent large deals have included AbbVie Inc's $54 billion acquisition of Shire Plc and Medtronic Inc's acquisition of Covidien Plc for $43 billion.
Citi is acting as financial adviser to Roche, while Centerview Partners and Goldman Sachs are acting for InterMune.
Roche said it would commence a tender offer to acquire all outstanding shares in the U.S. firm no later than Aug. 29.
(Editing by Tom Pfeiffer)
By Ben Hirschler and Caroline Copley
Stocks treated in this article : Pfizer Inc.
, Alexion Pharmaceuticals, Inc.
, BioMarin Pharmaceutical Inc.
, Illumina, Inc.
, InterMune Inc
, Medtronic, Inc.
, Covidien plc
, AstraZeneca plc
, CHUGAI PHARMACEUTICAL CO., LTD.
, Roche Holding Ltd.
, Shire PLC
, AbbVie Inc