Adult T-cell leukemia (ATL) is a rare and aggressive type of blood cancer that affects T-cells, a type of white blood cell crucial for the immune system. It is primarily caused by infection with the human T-lymphotropic virus type I (HTLV-I), which is transmitted through blood, sexual contact, or from mother to child during breastfeeding. Symptoms of ATL can include swollen lymph nodes, skin lesions, fatigue, and weight loss. The disease can progress rapidly, and treatment options may involve chemotherapy, targeted therapy, or stem cell transplantation, depending on the individual case and overall health of the patient.