ALK-positive histiocytosis associated with chronic lymphocytic leukaemia/small lymphocytic lymphoma: a multitarget response under ibrutinib

ALK-positive histiocytosis is a recently described entity with few reported cases in literature. Herein, we report an unusual case of ALK-positive histiocytosis showing an Erdheim-Chester disease (ECD)-like presentation, occurring in a 37-year-old woman with a 2-year history of chronic lymphocytic leukaemia (CLL). Our CLL patient relapsed 6 months after the end of fludarabine, cyclophosphamide and rituximab frontline therapy and complained of lower limb pains. A bone marrow biopsy was performed and showed concomitant CLL/small lymphocytic lymphoma and ALK-positive histiocytosis with an identical immunoglobulin heavy-chain gene rearrangement in both neoplasms, suggesting clonal relationship. After 4 years under ibrutinib therapy, our patient remains free of both diseases. This report extends the spectrum of composite hematolymphoid neoplasms and shows thatALKrearrangement should be considered in all histiocytosis subtypes. Moreover, both tumours eradication under ibrutinib suggests that BTK inhibitors may also be effective in histiocytic neoplasms.

Automated summary

This report describes an unusual case of ALK-positive histiocytosis with an Erdheim-Chester disease-like presentation in a 37-year-old woman with chronic lymphocytic leukaemia. The patient experienced a relapse of CLL 6 months after frontline therapy, but after 4 years of ibrutinib treatment, remains free of both diseases. The study suggests the potential efficacy of BTK inhibitors in histiocytic neoplasms.