context: If you have leukemia or lymphoma, you may need a stem cell transplant. These cells help replace cells damaged by the cancer. They also let your body recover faster from intense chemotherapy and radiation treatments. For some, it may be the best -- or only -- approach. They grow inside your marrow, the soft tissue of your bones. They're also in your blood, as well as blood from umbilical cords. As they mature, blood stem cells change into three types of cells your body needs: Platelets that help your blood clot Red blood cells that give your body oxygen White blood cells that fight off illness There are two types of transplants. Your doctor will decide which is best for you. In an autologous ( AUTO) transplant, doctors take healthy stem cells from your bone marrow or blood. They're frozen and carefully stored. Since they're outside your body, they aren't harmed during the chemotherapy or radiation treatments you'll need to get rid of your cancer cells. After your treatment ends, your thawed stem cells are returned to your bloodstream through an IV. They'll find their way back to your bone marrow. Once there, they help your body make healthy blood cells again. In an allogeneic, or ALLO, transplant, you get healthy stem cells from a donor. It's important that the donor's bone marrow closely matches yours. If it doesn't, your body may reject their cells. Your donor might be a family member. You can also get stem cells from someone you don't know. Before an ALLO transplant, you'll get chemotherapy, radiation, or both. This wipes out your own stem cells and gets your body ready for the new ones soon after your treatment is done. If your doctor can't find a donor, he may use cells from donated umbilical cord blood. After a baby is born, blood rich in stem cells remains in the discarded cord and placenta. It can be frozen and stored in a cord blood bank until its stem cells are needed. Cord blood is tested before it's banked. This lets doctors quickly check to see if there's a match for you. Plus, the pairing doesn't have to be as perfect as it would be from a donor. If you're being treated with your own stem cells, you may have high-dose chemotherapy first. This can cause side effects. What and how severe they are depend on the dose. You might have: Nausea Vomiting Fatigue Bleeding Severe infections That doesn't sound great, but advances in cancer treatment can make them easier to live with. When you get stem cells from a donor or cord blood, there's a risk of something called graft-vs.-host disease. It's when your body fights to get rid of the new cells, or the cells launch an attack against you. It could happen right after the transplant or not until a year later. Thanks to strides in the matching process in the past decade or so, your odds of having more problems from the treatment are much lower than they used to be. You'll also get medicine after your transplant that works to keep those problems at bay. Still, if you're older, it can be harder for you to manage side effects. Also, it's more likely you'll have another health condition like high blood pressure or diabetes. Your doctor may want you to have a reduced-intensity, or âmini,â stem cell transplant. You'll start out with a lower dose of chemo and radiation before you get the stem cells. It's less taxing on your body, and new cells can still grow and fight your cancer. They sound like special cells that fight cancer. They aren't. They're cells that advance cancer. Experts used to think all cancer cells were the same. Now, there's reason to believe that special, fast-growing cancer stem cells keep your disease alive by reproducing. If that's true, in the next few years, the focus of treatments could shift from trying to shrink tumors to trying to kill this type of cell.