STAT3 and rheumatoid arthritis: Although STAT3 mutation has not yet been correlated to RF and anti-CCP in LGL leukemia, LGL leukemia patients with concomitant RA have higher levels of both RF and anti-CCP than general RA populations, with one study observing 88% anti-CCP positivity and 82% RF positivity (30) and another showing 95% anti-CCP positivity (33).