There are plenty of organizations that provide information on cancer much better than I can. I have provided links to their cancer-specific sites at the bottom of this page. Here is my take.
We are made of cells, all of which have specific jobs. Our bodies have a very organized, orderly way of reproducing these cells as they get worn out and die off. Cancer occurs when one normal cell divides into abnormal cells instead.
These abnormal cells don't actually do much of anything, except proliferate, and that's the problem. The first abnormal cells divide into two more abnormal cells, which each divide into two more. This continues unchecked until there are so many abnormal cells that they start to negatively affect normal body functions, simply by just being in the way.
What about ALL?
With Acute Lymphoblastic Leukemia (ALL), it starts in the bone marrow.
The bone marrow is our blood cell factory. When abnormal cells (cancer cells) begin taking over that space, there is less room for the normal cells to divide. The bone marrow hardens as it gets packed with abnormal cells, which eventually start to spill into the bloodstream. Red and white blood cells, which carry oxygen and protect our bodies from infections, respectively, are crowded out and diminished. This leads to constant fatigue and being very susceptible to bacterial infections and viruses. Platelets become diminished as well, causing easy bruising and inability to clot blood.
The B-Cell subtype of ALL occurs in cells that would normally become B-cell lymphocytes (a type of white blood cell). It is the more common type of ALL. About 90% of children can be cured.
How Did Landon Get Here?
In Landon's case, he picked up a particularly nasty cough and a low fever. Some Tylenol got rid of the fever, but the cough stuck around for a week and seemed to be getting worse. He just seemed drained all of the time and looked pale often. The fever returned, which started a cycle of pediatrician visits, missed school days, and two Urgent Care visits for hives - what seemed like a possible allergic reaction to antibiotics, but may have been just his body reacting to the leukemia. At Urgent Care, steroids were provided for the hives, which in retrospect could have killed off some of the leukemic cells that may have spilled into his bloodstream. This matters because it could have hidden the leukemia in the initial blood tests, which look for blast cells that are indicative of leukemia. The doctors had a hard time identifying what the problem was because no blast cells were present in the blood cultures. It took a bone marrow biopsy from his hip to confirm it.