Additional Study Information: This study is being done to answer the following questions: Will patients that are 75 years of age or older who were recently diagnosed with Diffuse Large B Cell Lymphoma (DLBCL) be able to take the study drug CC-486 (oral azacitidine) plus the standard drug therapy that fights cancer cells for at least 4 cycles of therapy (a cycle = 21 days; 4 cycles is 12 weeks): without significantly more side effects than patients taking the standard drug therapy alone? Have longer, shorter, or the same amount of time without the disease getting worse (progression) than patients taking the standard drug therapy alone? Live longer, live the same amount of time, or live a shorter amount of time than patients taking the standard drug therapy alone? We will also compare any side effects that participants may have and participants' well-being when taking the study drugs and for up to three years after starting to take these drugs to treat the cancer. We are doing this study because we want to find out if this approach is better or worse than the usual approach for the DLBCL. The usual approach is defined as care most people get for DLBCL.