A closely watched study of GlaxoSmithKline plc's Breo Ellipta respiratory treatment failed to prove that it extends patients' lives, denying the drugmaker a much-needed marketing edge in its most lucrative - but declining - medicine category. It was a disappointing deja vu for the British drugmaker, which previously failed to prove the same benefit for its much older respiratory treatment Advair, long the company's top seller with revenue of $8.3 billion as recently as 2013.