RATIONALE: PEG-interferon alfa-2b may interfere with the growth of cancer cells and slow the growth of mycosis fungoides/Sezary syndrome. Ultraviolet light therapy uses a drug, such as psoralen, that is absorbed by cancer cells. The drug becomes active when it is exposed to ultraviolet light. When the drug is active, cancer cells are killed. Giving PEG-interferon alfa-2b together with ultraviolet light therapy may kill more cancer cell.