Lymphoma and leukemia are distinct blood cancers, though often discussed together due to their shared cellular origins. Understanding their differences is important for accurate diagnosis and treatment.
Understanding Lymphoma
Lymphoma is a cancer that begins in lymphocytes, which are a type of white blood cell crucial for the immune system. These cells are primarily located in the lymphatic system, a network of tissues and organs that includes the lymph nodes, spleen, thymus, and bone marrow. When lymphocytes undergo abnormal changes and multiply uncontrollably, they can form solid tumors, typically within the lymph nodes.
There are two main categories of lymphoma: Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL). Hodgkin lymphoma is distinguished by the presence of specific abnormal cells called Reed-Sternberg cells, which are large, often multinucleated cells identified under a microscope. Non-Hodgkin lymphoma encompasses a more diverse group of lymphomas that do not contain Reed-Sternberg cells and can originate from either B-cells or T-cells. Non-Hodgkin lymphoma is significantly more common than Hodgkin lymphoma, accounting for approximately 90% of all lymphoma diagnoses.
Lymphoma can manifest where lymphatic tissue is present, including lymph nodes, spleen, and bone marrow. Symptoms often include enlarged lymph nodes, fever, night sweats, and unintended weight loss.
Understanding Leukemia
Leukemia is a cancer of the blood-forming tissues, primarily the bone marrow. It is characterized by the rapid and uncontrolled production of abnormal white blood cells. These abnormal cells, often immature, build up in the bone marrow and blood, crowding out healthy blood cells and impairing their function. This can lead to a shortage of normal white blood cells, red blood cells, and platelets.
Leukemia is classified based on two main factors: the speed of its progression (acute or chronic) and the type of white blood cell affected (myeloid or lymphocytic). Acute leukemias progress rapidly and involve immature blood cells, requiring immediate treatment. Chronic leukemias typically worsen slowly and involve more mature, but still abnormal, blood cells, sometimes with few or no symptoms initially.
Based on the cell type, leukemia is either lymphocytic, affecting lymphoid cells that develop into lymphocytes, or myeloid, affecting myeloid cells that develop into other white blood cells, red blood cells, or platelets. These classifications lead to the four main types of leukemia: Acute Lymphocytic Leukemia (ALL), Acute Myeloid Leukemia (AML), Chronic Lymphocytic Leukemia (CLL), and Chronic Myeloid Leukemia (CML). ALL is the most common leukemia in children, while AML and CLL are more common in adults.
Distinguishing and Connecting Lymphoma and Leukemia
While both lymphoma and leukemia involve white blood cells, their primary distinction lies in where they originate. Lymphoma typically begins in the lymphatic system, forming solid tumors, most commonly in the lymph nodes. In contrast, leukemia primarily affects the bone marrow, leading to an overabundance of abnormal white blood cells circulating in the blood. Leukemia is often described as a “liquid cancer” because it does not form solid tumors.
Despite these differences, both conditions arise from mutations in white blood cells and share common cellular origins. This shared lineage means that while distinct, there can be overlap or even transformation between the two.
In some cases, a slow-growing lymphoma can transform into a more aggressive form, which may sometimes involve features seen in leukemia, or vice versa. For example, chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are considered the same disease, but are named based on where the cancerous cells are predominantly found; CLL if in the blood and bone marrow, and SLL if in the lymph system. Additionally, a transformation known as Richter’s transformation can occur, where CLL changes into a more aggressive lymphoma, most commonly diffuse large B-cell lymphoma. This potential for transformation or shared cellular characteristics explains why these two distinct cancers are often discussed together.