Treatment of multisystem Langerhans cell histiocytosis. Results of the DAL-HX 83 and DAL-HX 90 studies. DAL-HX Study Group.

BACKGROUND: The prognosis of children with multisystem Langerhans cell histiocytosis (LCH) has improved with the application of chemotherapy. However, treatment strategies used varied from conservative approach with treatment only during disease exacerbation to intensive chemotherapy starting immediately after diagnosis. No single drug or regimen has been proven to be superior to the others. Thus, optimal treatment of multisystem LCH remains still an unsolved problem. PATIENTS: Three hundred and twenty-four patients enrolled in the DAL-HX 83 and DAL-HX 90 studies were retrospectively re-evaluated by using the current definition for disease extent. Sixty-three patients fulfilling the criteria for multisystem LCH (involvement of > or = 2 organ systems) were object of the present study. These were 33 males and 30 females, median age at diagnosis 11.5 months (range, birth-13 years 2 months). The median observation time was 7 years 6 months (4 years-11 years 8 months).
METHODS: All patients had morphologically confirmed diagnosis, which was additionally verified through demonstration of CD1a antigen, presence of Birbeck granules or central pathologic review. Uniform evaluation including a complete medical history and physical examination, laboratory tests (complete blood count, liver function tests, coagulation profile) and radiographic survey (skeletal survey and/or radionuclide bone scan) was performed in all patients. Additional investigations (bone marrow tap, CT, MRI etc.) were performed upon specific indications. The 63 patients with multisystem LCH were evaluated with respect to response to therapy, clinical course, outcome and development of permanent disabilities. The results of the DAL-HX studies were compared with the results of the first randomized international clinical trial on multisystem LCH (LCH-I).
RESULTS: Response to 6 weeks of initial therapy showed a clear discrimination between responders and non-responders, with only 6% of the patients having intermediate response. When correlated to survival response to initial therapy appears to be a powerful prognosticator in multisystem LCH. There were some typical patterns of clinical course. Complete disease resolution at some point of the clinical course was documented in 50 (79%) patients. Thirty-five of them remained disease free, while 15 experienced one or more episodes of disease reactivation. Chronic reactivating course without complete disease resolution was observed in one patient. Deteriorating disease with fatal outcome was shown in 12 (19%) patients. The overall survival after 5 years of observation was 81%. One or more disease-related permanent disabilities were documented in 24 patients, in 4 of them these were shown at diagnosis and in 20 patients these developed after therapy had been commenced. Despite more intensive chemotherapy, the overall survival in DAL-HX 83/90 cohort was comparable with that in LCH-I studies. However, LCH-I compares unfavorably to DAL-HX 83/90 in some very important aspects. With respect to reactivation rate, reactivation free interval and development of permanent disabilities better results were achieved with the more intensive initial and prolonged continuation therapy concept of the DAL-HX studies. Even after extended analysis it remains unclear whether the superiority of the DAL-HX studies has to be attributed to the administration of continuous steroids, to the combination of vinblastine and etoposide, or to the prolonged continuation therapy including mercaptopurine. Answers to these questions are expected from the ongoing international clinical trial LCH-II.