Sometimes LCH continues to grow or comes back after treatment.

Progressive LCH describes LCH that continues to grow, spread, or get worse. Progressive disease may be a sign that the LCH has become refractory to treatment.

Refractory LCH describes LCH that does not respond to initial treatment.

Recurrent or reactivated LCH describes LCH that has come back after it has been treated.

Many patients with LCH get better with treatment. However, when treatment stops, new lesions may appear or old lesions may come back. This is called reactivation (recurrence) and may occur within 1 year after stopping treatment. Patients with multisystem disease are more likely to have a reactivation. Common sites of reactivation are bone, ears, or skin. Diabetes insipidus also may develop. Less common sites of reactivation include lymph nodes, bone marrow, spleen, liver, or lung. Some patients may have more than one reactivation.