Eltrombopag is a highly effective treatment for immune thrombocytopenia (ITP). Cases of durable remission after the discontinuation of eltrombopag in adult ITP have recently been reported; however, the frequency and mechanisms responsible for this phenomenon remain unknown. In the present study, we examined the phenotypes of lymphocytes in ITP to clarify whether they predict outcomes after the discontinuation of eltrombopag. We examined 56 adult newly diagnosed ITP patients treated with eltrombopag after a median time from diagnosis of 48 months. Among the 38 patients who achieved complete remission, eltrombopag was discontinued in 26. Among the 26 patients, 12 (46.2%) had an immediate relapse after discontinuing eltrombopag and 16 (53.8%) showed sustained response without additional ITP therapy, despite discontinuing eltrombopag, with a median follow-up of 52 months. No significant differences were observed in platelets, the median duration of eltrombopag, the absolute number of T, B, and NK cells at the initiation of eltrombopag between patients who sustained response and those who relapsed after discontinuing eltrombopag. However, the number of B and NK cells at the discontinuation of eltrombopag was higher in patients who sustained response than in those who relapsed (p=0.022 and p=0.012, respectively). The present results indicate that the absolute number of B (≥ 0.20 x 109/L) and NK (≥ 0.36 x 109/L) cells at the discontinuation of eltrombopag contributes to the prediction of outcomes.
