Adult T-cell Leukemia/Lymphoma (ATLL) is a type of cancer that affects the T-cells, a kind of white blood cell crucial for the immune system. It is primarily caused by the Human T-cell Lymphotropic Virus type I (HTLV-I), which is transmitted through blood, sexual contact, or from mother to child during breastfeeding. ATLL can manifest in various forms, including aggressive leukemia or lymphoma, and is more common in certain regions, particularly in Japan and parts of Africa. Symptoms of ATLL may include swollen lymph nodes, skin lesions, and fatigue. Diagnosis typically involves blood tests, imaging studies, and a biopsy of affected tissues. Treatment options vary and may include chemotherapy, antiviral medications, and stem cell transplants, depending on the disease's stage and severity. Early detection and intervention are crucial for improving outcomes.