What are pediatric leukemias and lymphomas?

Leukemias and lymphomas are cancers of the blood and immune system. The basic building blocks of humans are called cells, and the blood consists of three types of cells called white blood cells, red blood cells and platelets. All of these blood cells develop from a specialized bone marrow stem cell called a hematopoietic stem cell. Hematopoietic stem cells are different from other types of stem cells in that they only form blood. Cancers can arise at various stages of development between the stem cell and fully mature blood cells.

What are these blood cells normally doing, and what kinds of cancers do they form?

White blood cells: White blood cells form our immune system. There are several types of white blood cells, and all can turn into cancers.

  • Myeloid cells – These are the “first responders” of the immune system. They are programmed to recognize bacteria, molds and other microbes. Myeloid cells develop in the bone marrow from “myeloid precursors”, which can sometimes become a type of leukemia called acute myeloid leukemia, or AML. Myeloid precursors can also form rarer types of childhood cancer, including juvenile myelomonocytic leukemia (JMML) and chronic myeloid leukemia (CML).
  • Lymphoid cells – These immune cells can be “trained” to remember prior infections or vaccines. They provide a tailored response to specific infections. Lymphoid cells also come in different “flavors”. One type, called B-cells, produces antibodies. A second type, called T-cells, can either help educate other immune cells, or they can be trained to attack and kill infected cells or cancer cells. A third type, called NK (natural killer) cells, can also be trained to attack and kill infected cells and cancer cells.

Lymphoid cells develop from “lymphoid precursors” in the bone marrow or thymus. They can form leukemias or lymphomas, which are discussed in more detail below. We sometimes use lymphoid cells to treat cancers. For example, we can engineer T-cells to kill leukemia and lymphoma. Researchers at Washington University are pioneering techniques to use NK cells to kill AML.

  • Red blood cells: Red blood cells carry oxygen around our bodies. Red blood cell cancers are rare in children. However, we rely heavily on red blood cell transfusions to help sustain children who are receiving chemotherapy and cannot make their own blood.
  • Platelets: Platelets are small cells that help the blood clot. They are produced in the bone marrow by a type of “platelet precursor” called a megakaryocyte. Megakaryocytes sometimes turn into leukemia, though this is relatively rare. As with red blood cells, we rely heavily on platelet transfusions to help sustain children who are receiving chemotherapy and cannot make their own blood.
  • Stem cells: Hematopoietic stem cells are rare cells within the bone marrow that sustain blood production and help blood regenerate after chemotherapy or radiation. These are also the cells that we use to regenerate the immune systems of children who receive bone marrow transplants. Hematopoietic stem cells are unique because they can form white blood cells or red blood cells or platelets.

What is the difference between leukemia and lymphoma?

The designation of a cancer as a leukemia versus a lymphoma reflects where the cancer is primarily located (bone marrow or lymph nodes). For simplicity’s sake, one can think of leukemias as cancers that primarily invade the bone marrow, whereas lymphomas primarily invade lymph nodes, spleen or thymus. This distinction is not absolute – some leukemias invade lymph nodes, and some lymphomas invade bone marrow.

What is acute myeloid leukemia, or AML?

Acute myeloid leukemia is a cancer of myeloid cells – the first responders of the immune system. It is often called AML, for short. AML can occur at any age, but childhood and adult AML often have different genetic mutations and different outcomes. Treatments include chemotherapy and sometimes bone marrow transplants.

AML research is one of our major focuses at Washington University. We are working to understand why children get AML, and we are working to identify drug targets that might be particularly useful for treating children with AML. Finally, we have developed clinical trials to infuse immune cells that target and kill AML.

What is acute lymphoblastic leukemia, or ALL?

Acute lymphoblastic leukemia is a cancer of lymphoid progenitors – the educated part of the immune system. It is often called ALL, for short. ALL is the most common pediatric cancer, and it can occur as either B-cell Acute Lymphoblastic Leukemia (B-ALL) and T-cell Acute Lymphoblastic Leukemia (T-ALL). Both almost always arise from immature “lymphoid precursors” meaning that they are more developed than a stem cell, but not so developed that they resemble fully functional lymphoid cells. Treatments typically involve chemotherapy, immune therapies and sometimes bone marrow transplants.

We have a number of clinical trials aimed at improving outcomes for people with ALL. Some of the trials aim to tailor chemotherapy doses for individual patients – we want to deliver enough chemotherapy to cure the disease, but not any more than is necessary. Some clinical trials add antibodies that specifically target ALL cells. This adds another powerful anti-leukemia agent to the regimen, and it can sometimes replace more toxic chemotherapy.

We also have an active cellular therapies program that focuses primarily on treating B-ALL that are resistant to other drugs. We infuse T-cells (immune cells) that are engineered to target and kill the ALL cells.

What is Hodgkin’s lymphoma?

Hodgkin’s lymphoma is a cancer that primarily involves cells in the lymph nodes. It occurs most often in teenagers and young adults. Treatments include chemotherapy and sometimes radiation. Many of our clinical trials now add antibodies and other agents to ramp up the immune system to destroy the cancer cells. The goal is to replace some of the more toxic therapies (chemotherapy and radiation) with these immune therapies while still achieving excellent cure rates.

What is a T-cell lymphoma?

T-cell lymphomas are cancers of lymphoid progenitors. In children, T cell lymphomas usually closely resemble T-ALL, but the cancer involves the lymph nodes more than the bone marrow. Treatment usually requires chemotherapy; radiation is rarely required for these patients.

What is a B-cell lymphoma?

B-cell lymphomas are cancers of lymphoid progenitors. They can occasionally resemble B-ALL, but most are either diffuse large B-cell lymphomas or Burkitt’s lymphomas. Both diffuse large B-cell lymphomas or Burkitt’s lymphomas form from cells that are more “mature” than B-ALL, meaning they look even less like a stem cell and more like a fully developed lymphocyte. Treatment typically requires a very different chemotherapy regimen than is used for B-ALL.

Are there other types of leukemias and lymphomas that you have not covered above?

There are rarer types of childhood leukemias and lymphomas, including juvenile monomyelocytic leukemia, chronic myeloid leukemia, anaplastic large cell lymphomas and other rarer lymphomas. We routinely treat these diseases, even though they are comparatively rare. In some cases, we have open clinical trials and ongoing research.