Molecular Basis of Langerhans and Non-Langerhans Cell Histiocytic Neoplasms and Castleman Disease

The study team will examine genetic changes, also known as mutations, in the DNA of participants' blood, or if applicable, bone marrow specimen. These types of tests are increasingly used by doctors to improve the accuracy of diagnosis and make decisions during care. This study seeks to understand how many patients will benefit from this testing, and in what ways. The results of this portion of the study are placed in the individual's medical record and are communicated back to each participant.