Tests show that the tumors are gone but his lymph nodes are still enlarged. what does that mean?

Tumors of the Lymph : Lymphomas are tumors of the lymph nodes which require treatment with chemotherapy. They would shrink in size and go away if the treatment is working well. So it depends on the size of the lymph nodes. Anything larger than mbarble size(about one inch) would be abnormal and requires medical attention to confirm if the tumor has indeed gone away completely or only partially.