A look at the US rheumatoid arthritis market shows exactly why filgotinib was going struggle – even before this week’s US complete response letter. Despite the arrival of Pfizer’s Xeljanz, the first Jak inhibitor, in 2012, the biggest-selling RA treatments this year will have been available for 20 years or more. The dominance of TNF antibodies is arguably more about the power of patents than efficacy, of course; Abbvie’s Humira will face its first biosimilar competition in the US in 2023, while a recent patent win for Amgen could see Enbrel enjoy an incredible 31 uncontested years on the market. Before the FDA turned down filgotinib’s approval the Gilead/Galapagos Jak1 was seen generating a mere $700m in US sales in 2026, according to EvaluatePharma's sellside consensus, a figure that will now be heading down. Still, analysts have long held wildly different opinions about the project's prospects, with those on the low side citing a hugely competitive market in which neither partner is experienced. This probably also explains the success predicted for Abbvie’s Rinvoq, a view that will only become more entrenched if the drug ends up boasting the best profile across the Jak class, something that looks increasingly likely.