What Is Cancer? Cancer is actually a group of many related diseases that all have to do with cells. Cells are the very small units that make up all(51)things, including the human body. There are billions of cells(52)each person's body. Cancer happens when cells that are not normal grow(53)spread very fast. Normal body cells grow and divide and know when to stop growing. Over time, they also die.(54) these normal cells, cancer cells just continue to grow and divide out of control and don't die. Cancer cells usually group together to form. tumors (肿瘤). A growing tumor becomes a lump of cancer cells(55) can destroy the normal cells around the(56) and damage the body's healthy tissues. This can make someone very(57) . Sometimes cancer cells break away from the original tumor and travel to other areas of the(58) , where they keep growing and can go on to form. new tumors. This is how cancer(59) . The spread of a tumor to a new place in the body is(60) metastasis (转移). People with cancer may feel pretty sick at times--but can usually still do lots of normal things.(61) they are very sick, kids and teenagers with cancer may still be able to go to school. They may be tired or bruise (出现青肿) easily, but they(62) sometimes go to camp, movies, and sleepover (在外过夜的) parties. People with cancer still like the same things they did(63) they got sick. Cancer in kids is rare--but today, many kids who do get cancer go on living normal lives. The number of kids who beat cancer goes(64)every year because of new cancer treatments. So a lot of kids with cancer will some day drive cars, go to college, have careers, and even get(65) and have families of their own.