Response to HU therapy. Best clinical responses of 15 relapsed/refractory LCH patients treated with HU (± MTX) therapy. Eight of 15 patients (53%) showed CR, 4 of 15 (27%) showed PR, 2 of 15 (13%) showed SD, and 1 of 15 (7%) showed PD when treated with HU therapy alone, or in combination with MTX. Six of 15 patients (40%) progressed or relapsed (2 off HU therapy, and 4 on HU therapy); 2 of 6 patients (33%) had PR after HU reinitiation, and MTX was added in both cases, with CR in patient #14. The addition of MTX to patient #11 lead to ongoing improvement, but not CR. Patient #5 had initial PR to HU and no additional benefit after MTX was added.