World Leukemia Day is observed every year on September 4 to raise awareness about leukemia, a cancer of the blood and bone marrow that affects thousands of people across all age groups. Unlike solid tumors that form visible lumps, leukemia often develops quietly, with symptoms that are easy to dismiss as fatigue, a lingering cold, or seasonal weakness. This is exactly why World Leukemia Day 2026 focuses on the silent signs of blood cancer — helping people recognize warning signals early, when treatment is most effective.