Pathology refers to the examination of tissue under a microscope to find out whether it’s cancerous or non-cancerous and to determine the type of tumour it is. Different types of tumours can affect the lymphatic system.
Non-Hodgkin lymphoma (NHL) is a cancer that starts in a type of white blood cell called the lymphocyte. The way that NHL develops and spreads depends on the type of lymphocyte the lymphoma starts in. There are 2 main kinds of lymphocytes: B cell and T cell. NHL can start in either of these cells.
NHL usually starts in a group of lymph nodes in one part of the body, but NHL can begin wherever lymphocytes or lymphatic tissue are found. Some places in the body where NHL can occur include:
Types of NHL
Non-Hodgkin lymphomas (NHL) are classified according to the World Health Organization (WHO) classification system. There are 2 main types of NHL based on the type of lymphocyte in which the cancer started:
- B-cell lymphoma – most common type
- Most types of NHL (about 85%) develop from B cells.
- T-cell lymphoma
- T-cell lymphomas develop from T cells. They are less common than B-cell lymphomas.
- Natural killer (NK) cells are another type of lymphocyte that attack foreign cells. NK-cell lymphomas are included in the T-cell group.
NHL is not just one cancer. There are over 30 different subtypes of non-Hodgkin lymphoma. The cells of the various subtypes look different under a microscope, and they grow and spread differently.
The WHO classification system also considers:
- the size, shape and appearance (morphology) of the cells under the microscope
- the growth patterns of the cells
- genetic or chromosome characteristics of the cells
- immune features of the lymphoma cells, including certain markers on the surface of the cell
- how the disease grows in the body
Lymphomas and lymphoid leukemias are both included in the WHO classification for lymphomas because they both start in the same type of cell (lymphocyte). They are basically the same disease, but differ in how and where they present.
Once the specific type of NHL has been diagnosed, the doctor will also consider:
- the grade of the tumour (how abnormal the cancer cells look and behave and how slow or fast the lymphoma cells grow)
- Before the WHO classification system, other systems, such as the Working Formulation, were used to classify lymphomas according to their aggressiveness. The subtypes of NHL were placed into low-, intermediate- and high-grade groups. Although these systems are rarely used today, doctors still use the idea of low-grade or slow-growing (indolent) NHL and high-grade or fast-growing (aggressive) NHL to help determine prognosis and plan treatment.
- the stage of the cancer, including if it has spread (metastasized) and where it has spread
- prognostic factors (special characteristics that might influence the course of the disease)
- survival statistics for the particular type and stage of cancer
All of this information helps the doctor make a treatment plan.
See a list of questions to ask your doctor about pathology and staging.