DLBCL is a cancer of B lymphocytes (B cells). In DLBCL, B cells stop responding to signals that usually limit the growth and reproduction of cells. This causes the B cells to undergo a malignant transformation (acquire the properties of cancer) where they become much bigger than normal lymphocytes.
This subtype of lymphoma is called diffuse large B cell because of the way the cancerous large B cells are scattered throughout (diffuse) the lymph nodes when examined with a microscope. This growth pattern contributes to the aggressive behaviour of DLBCL.
DLBCL is typically an aggressive (fast-growing) lymphoma (also known as high-grade or acute). It can occur in lymph nodes (‘nodal’) or outside of the lymphatic system (‘extranodal’) in the gastrointestinal tract, testes, thyroid, skin, breast, bone, or brain. Extranodal disease usually indicates advanced stage disease.
DLBCL can present de novo (new) or as a transformation of other low-grade B cell lymphomas like follicular or chronic lymphocytic leukaemia/small lymphocytic lymphoma. The de novo DLBCL cases have better prognoses than the transformed cases. There are many subtypes of DLBCL, and a patient’s DLBCL subtype may affect their prognosis, response to treatment, and treatment options.
Subtypes of DLBCL
|Intravascular large B cell lymphoma (ILCL)|
Lymphoma cells (cancer cells) circulate in the blood and block small blood vessels. It can affect small blood vessels in organs such as the brain, spinal cord, kidneys, lungs, and skin. ILCL usually occurs in middle-aged or elderly people. ILCL may also be called intravascular lymphomatosis or malignant angioendotheliomatosis.
Primary cutaneous DLBCL, leg type
Characterised by skin lesions mainly on the legs, but the disease can also involve the trunk, arms, legs, buttocks or anywhere on the body. These lymphomas can spread to other areas than just the skin. Usually occurs in elderly people.
Primary DLBCL of the central nervous system (CNS)
Cancer cells from lymph tissue form in the brain and/or spinal cord. Primary CNS lymphoma can also start in the eye (called ocular lymphoma). If lymphoma develops somewhere else in the body and then spreads to the brain and/or spinal cord, it is called secondary DLBCL of the CNS.
Primary effusion lymphoma (PEL)
Causes an abnormal buildup of fluid (lymphoma cells found in this fluid) in the cavity (space) around the lungs, the cavity around the heart, or the cavity in the abdomen. Usually occurs in people who are immunosuppressed or who are HIV-positive. It can sometimes occur in people who have had organ transplants. PEL is often linked with Epstein-Barr virus (EBV) or human herpes virus type 8. PEL may also be called body-cavity based lymphoma.
Primary mediastinal large B cell lymphoma (PMBCL)
Occurs in the thymus gland (small gland in centre of chest behind the breastbone) or in the centre of the chest (called the mediastinum). PMBCL is not common and often occurs in younger people. PMBCL may also be called mediastinal B-cell lymphoma or mediastinal (thymic) large B cell lymphoma.
T cell/histiocyte rich large B cell lymphoma
Rare morphological variant where large abnormal B cells are surrounded by abundant normal T cells and histiocytes (cells that migrate from bone marrow into tissues), which may obscure tumour cells. Usually occurs in middle-age people, often with advanced stage and involvement of lymphoma nodes, spleen, and bone marrow.
Most cases of DLBCL do not fall perfectly into a defined category, and they are considered DLBCL not otherwise specified (NOS). However, these NOS cases can be grouped into molecular subtypes according to their cell of origin.
Within the large category of DLBCL NOS, two distinct molecular subtypes have been recognised. These groups of patients may have a different prognosis with treatment:
- Germinal centre B cell (GCB): Patients with GCB type DLBCL generally have better outcomes compared to patients with the non-GCB type. GCB subtype has a complete response (CR) rate of about 70% to standard therapy.
- Activated B cell (ABC): ABC DLBCL has a more aggressive clinical course and a worse prognosis when treated with standard therapy. The complete response (CR) rate with standard therapy for ABC-type DLBCL is not more than 30% with a high chance of relapse within two years following treatment, hence patients with ABC subtype may benefit from clinical trial.