(This Dec.20 story corrects first paragraph to say the approval came four months ahead of schedule, not three months, after FDA clarification)

(Reuters) – The U.S. Food and Drug Administration said on Friday it had approved Daiichi Sankyo Co Ltd and AstraZeneca Plc’s drug to treat an advanced form of breast cancer, four months ahead of schedule.

AstraZeneca in March signed a licensing and collaboration deal that committed the British drugmaker to pay up to $6.9 billion to its Japanese partner Daiichi. (https://reut.rs/2sKMyIy)

The drug, Enhertu, comes with a boxed warning, the FDA’s strictest warning, flagging increased risk of lung disease and embryo-fetal toxicity.

The agency said further clinical trials may be required to verify and describe the benefits of Enhertu, which is still under development.

Enhertu, also known as DS-8201, targets HER2 protein, a major trigger of uncontrolled cell growth in about 20% cases of breast cancer, where Roche Holding AG has been a pioneer with its aging $7 billion-a-year best-seller Herceptin.

The FDA’s accelerated approval program allows a speedier market entry to medicines that fill an unmet medical need for a serious condition.

(Reporting by Dania Nadeem in Bengaluru; Editing by Shinjini Ganguli)