Collection of Blood From Patients With Cancer, Other Tumors, or Tumor Predisposition Syndromes for Genetic Analysis

Background: \- Some genes may be associated with a greater chance of side effects during cancer treatment. These genes may also make certain treatments less effective. Researchers want to collect blood or cheek swab samples from people having cancer treatment to study these genes. Objectives: \- To obtain a blood or cheek swab sample to study genetic differences that may affect cancer treatment. Eligibility: \- Individuals with cancer who are being treated at the National Cancer Institute. Design: * Participants will provide a blood sample for study. * Participants who have blood-based cancer, such as leukemia, will provide a cheek swab sample. * If the blood or cheek swab sample does not have enough genetic material for analysis, an additional sample may be collected.