Blood cells are made inside your bone marrow, and that’s where leukemia starts. It causes your body to make white blood cells that grow out of control and live longer than they’re supposed to. And unlike normal white blood cells, they don’t help your body fight infection.

There are many different forms of leukemia. Some get worse quickly (acute). You’ll probably feel very sick very suddenly, like you’ve come down with the flu. Other forms can take years to cause symptoms (chronic). Your first clue may be abnormal results on a routine blood test.

Most signs of leukemia happen because the cancer cells keep your healthy blood cells from growing and working normally.

Because your white blood cells don’t fight infection well, you’ll get sick more often and take longer to get over it. You may get a lot of fevers and have night sweats.

Cancer cells can build up in your lymph nodes, tonsils, liver, and spleen and cause them to swell. You may feel lumps in your neck or armpit, or you may feel full after only eating a small amount. You may lose a lot of weight without trying. And the growth of cancer cells in your bone marrow sometimes causes bone pain.