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What is Which of the following drugs is used for the treatment of refractory histiocytosis : and explain in detail?
Treatment of LCH :
1. Single system disease  :

The clinical course of single system disease is usually benign with a high chance of spontaneous remission.
Therefore, treatment should be minimal and should be directed at arresting the progression of a bone lesion that could result in permanent damage before it resolve spontaneously.
Curettage or less often low dose local radiotherapy may accomplish this.

2. Multisystem disease :

It should be treated with systemic multiagent chemotherapy.
Any one, of following two should be included in regimen : 

i) Etoposide  
​ii) Vinblastin

For unresponsive disease following therapies are available :

i) Cyclosporine / antithymocyte globulin.
ii) Imatinib.
iii) 2-chlorodeoxyadenosine (Cladribine).
iv) Stem cell transplantation.