Competing interests: JK has received research grants paid to his institution from AbbVie, Eli Lilly and Company, Genentech, Gilead Sciences, Pfizer and UCB, and has provided expert advice to AbbVie, Amgen, Boehringer Ingelheim, Bristol-Myers Squibb, Celgene, Celltrion Healthcare, Eli Lilly and Company, Epirus Biopharmaceuticals, Janssen Biotech, Merck Sharp & Dohme, Myriad Genetics, Novartis Pharmaceuticals, Pfizer, Roche Laboratories, Samsung Bioepis, Sandoz and UCB. TD has received research grants or independent data monitoring committee honoraria paid to his institution from Celgene, GlaxoSmithKline, Samsung Bioepis, Roche Laboratories, Sanofi and UCB, and has provided expert advice to and/or had speaking engagements for Bristol-Myers Squibb, Celgene, GlaxoSmithKline, Merck Sharp & Dohme, Pfizer/Hospira, Samsung Bioepis, Roche Laboratories, Sanofi and UCB. PE has received research grants paid to his institution from and has provided expert advice to AbbVie, Bristol-Myers Squibb, Eli Lilly and Company, Merck Sharp & Dohme, Novartis, Pfizer, Samsung Bioepis, Sandoz, Roche Laboratories and UCB. TKK has received research grants paid to his institution from AbbVie, Merck Sharp & Dohme and Pfizer/Wyeth, and has provided expert advice to and/or had speaking engagements for AbbVie, Amgen, Biogen, Celltrion Healthcare, Merck Sharp & Dohme, Mylan NV, Orion, Pfizer, Samsung Bioepis, Sandoz, Sanofi Genzyme, Roche Laboratories and UCB. FCB has provided expert advice to and/or had speaking engagements for AbbVie, Amgen, Epirus Biopharmaceuticals, Merck Sharp & Dohme and Pfizer.