Phase I Master Protocol of Novel Combination Therapy for Patients With Relapsed or Refractory Aggressive B-Cell Lymphoma

To find the highest dose of a new drug that can be tolerated without causing severe side effects when receiving R-GDP or an equivalent regimen. This is done by starting at a dose lower than the one that is tolerated in patients when given on its own. Participants are given the new drug together with R-GDP and are watched very closely to see what side effects they have and to make sure the side effects are not severe. If the side effects are not severe, then new participants will be given a higher dose of the new drug. Participants joining the study later on will get higher doses of the new drug than participants who join earlier. This will continue until a dose is found that causes severe but temporary side effects. Doses higher than that will not be given.