 3. A documentation of diagnosis of hemophagocytic lymphocytosis, either newly diagnosed or relapsedrefractory by the treating physician and the PI in the patients chart. It must be noted that no diagnostic criteria have been established for diagnosis of HLH in adult patients as this was a hitherto poorly identified and considered to be a very rare disease in adults. We have seen an increasing number of cases of HLH at our institution over the last 2 years partly due to referrals and partly due to better understanding of the disease through discussions with our collaborators Dr Kenneth McClain and Dr Carl Allen at TCH experts in pediatric HLH. Adult HLH seems to occur more frequently post malignancy and has a more fulminant course than pediatric HLH. 