This study is being done to determine if the drug lenalidomide combined with full doses of EPOCH chemotherapy is effective for Human T-cell Leukemia Virus (HTLV)-associated Adult T-Cell Leukemia-Lymphoma (ATLL). EPOCH chemotherapy is a regimen comprised of multiple drugs. Additionally, the study is investigating what is the highest dose and longest duration this combination can safely be given to patients.

Lenalidomide and EPOCH Chemotherapy are both approved by the U.S. Food and Drug Administration (FDA) for other uses, but this is the first time these drugs will be tested together in patients with HTLV associated adult T-cell leukemia-lymphoma (ATLL).

Participation will take place in either 21 or 28-day cycles as determined by the study team. Participants will receive lenalidomide by mouth in combination with the usual chemotherapy drugs, EPOCH by intravenous injection. except for prednisone which is given by mouth. Participants may continue to take lenalidomide alone for up to 2 years until their disease becomes worse, the study doctor believes it is no longer working, or they desire to discontinue the study drugs.

In addition to a baseline scan, PET/CT scans will be performed after each completed treatment cycle.