CD80 and rheumatoid arthritis: Abatacept is the first in a class of agents for the treatment of rheumatoid arthritis (RA) that selectively modulates the CD80/CD86 : CD28 co-stimulatory signal required for T-cell activation.1 Abatacept has demonstrated efficacy in the treatment of RA.2, 3, 4, 5 Although abatacept has also demonstrated a favourable safety and tolerability profile in RA clinical trials, its potential risk for rare adverse events such as malignancies has not been addressed in the published literature.