ATL is a malignancy of T lymphocytes caused by HTLV-1 infection. It is classified into several clinical subtypes: acute, lymphomatous, chronic, and smoldering. The acute and lymphomatous forms are aggressive and have a poor prognosis, while the chronic and smoldering forms progress more slowly. Symptoms of ATL can include lymphadenopathy, hepatosplenomegaly, skin lesions, and hypercalcemia.
