Molecular Characterization of Viral-associated Tumors, Tumors Occurring in the Setting of HIV or Other Immune Disorders and Castleman Disease

* INCLUSION CRITERIA: Participants with one or more of the following: * HIV or other acquired immunodeficiency and cancer * Viral-associated cancer or cancer hypothesized to be caused by a virus * HIV-negative participants with cancer that commonly occurs in people with HIV --KSHV-associated malignancy or related diseases, such as Multicentric Castleman Disease (MCD) * A malignancy hypothesized to be caused by an endogenous retrovirus * Idiopathic Castleman disease Cancer diagnoses will be confirmed by the NCI Laboratory of Pathology (LP). A biopsy will be collected if sufficient archival tissue is not available. * Age \>=18 years. * ECOG performance status \<=2 (Karnofsky \>=60%) if biopsy to be performed is solely for the purposes of this protocol. Any ECOG performance status will be allowed if biopsy required for participant care or another NIH protocol that allows lower performance status or if enrollment on this protocol is only for the purposes of studying tissue that has already been collected. * Participants must have signed or be willing to sign an IRB-approved informed consent document that permits the use of the tumor and other samples for genomic-based molecular characterization projects. Telephone consent for use of archival tissue or tissue collected on another protocol or standard participant care will be permitted. * Co-enrollment on other HAMB, NCI, or NIH protocols is allowed EXCLUSION CRITERIA: * Inability to provide informed consent. * Pregnancy: Pregnant women will not be allowed to participate in this study because there is not a potential benefit.