Primary Mediastinal B-cell Lymphoma
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Primary mediastinal B-cell lymphoma, abbreviated PMBL or PMBCL, is a rare type of
lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). The name typically refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enlarged lymph node ...
that forms in the
mediastinum The mediastinum (from ;: mediastina) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is a region that contains vital organs and structures within the thorax, mainly the heart and its vessels, the eso ...
(the space in between the lungs) and predominantly affects young adults. While it had previously been considered a subtype of
diffuse large B-cell lymphoma Diffuse large B-cell lymphoma (DLBCL) is a cancer of B cells, a type of lymphocyte that is responsible for producing antibodies. It is the most common form of non-Hodgkin lymphoma among adults, with an annual incidence of 7–8 cases per 100,000 ...
;, the
World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
no longer classifies it as such, based on distinct clinicopathologic and molecular features.


Pathophysiology

PMLBCL arises from a putative thymic peripheral B cell. It has several distinctive biological features. Molecular analysis shows that PMLBCL is distinct from other types of
diffuse large B-cell lymphoma Diffuse large B-cell lymphoma (DLBCL) is a cancer of B cells, a type of lymphocyte that is responsible for producing antibodies. It is the most common form of non-Hodgkin lymphoma among adults, with an annual incidence of 7–8 cases per 100,000 ...
s (DLBCL). MAL gene expression is seen in 70%, unlike other diffuse large B-cell lymphomas.
Gene expression profiling In the field of molecular biology, gene expression profiling is the measurement of the activity (the gene expression, expression) of thousands of genes at once, to create a global picture of cellular function. These profiles can, for example, dis ...
shows considerable variance from other DLBCLs and similarity to Hodgkin disease. PMLBCL is
CD20 B-lymphocyte antigen CD20 or CD20 is B lymphocyte cell-surface molecule. It is a 33-37 kDa non-glycosylated protein. CD20 is expressed on the surface of B-cells from the pre-B phase, the expression is lost in terminally differentiated plasm ...
positive, expresses pan-B markers including CD79a, and has clonal immunoglobulin gene rearrangements and
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...
but paradoxically does not express
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
ic or cell surface immunoglobulin. Clinically, PMLBCL is unusual in several respects. Despite 80% PMLBCL being stage I or II, the presenting anterior
mediastinal The mediastinum (from ;: mediastina) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is a region that contains vital organs and structures within the thorax, mainly the heart and its vessels, the eso ...
mass is often over 10 cm and is locally invasive of lung, chest wall, pleura, and pericardium. At initial presentation, PMLBCL is usually confined to mediastinum, but its bulk, rather than additional adenopathy, can sometimes be palpated at the low neck. Increased LDH is seen in approximately 75%, but unlike other large cell lymphomas, no increase in
beta-2 microglobulin β2 microglobulin (B2M) is a component of MHC class I molecules. MHC class I molecules have α1, α2, and α3 proteins which are present on all nucleated cells (excluding red blood cells). In humans, the β2 microglobulin protein is encoded by t ...
is seen even when bulky which may relate to defective
major histocompatibility complex The major histocompatibility complex (MHC) is a large Locus (genetics), locus on vertebrate DNA containing a set of closely linked polymorphic genes that code for Cell (biology), cell surface proteins essential for the adaptive immune system. The ...
expression.


Diagnosis

Diagnosis requires a
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...
, so that the exact type of tissue can be determined by examination under a
microscope A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...
. PMBCL is a distinct type of lymphoma that shares some features with both
diffuse large B-cell lymphoma Diffuse large B-cell lymphoma (DLBCL) is a cancer of B cells, a type of lymphocyte that is responsible for producing antibodies. It is the most common form of non-Hodgkin lymphoma among adults, with an annual incidence of 7–8 cases per 100,000 ...
, and
nodular sclerosing Hodgkin lymphoma Nodular sclerosing Hodgkin lymphoma ("NSHL") or Nodular sclerosis is a form of Hodgkin lymphoma that is the most common subtype of HL in developed countries. It affects females slightly more than males and has a median age of onset at ~28 years. I ...
(NSHL). Tumors that are even more closely related to NSHL than typical for PMBCL are called
gray zone lymphoma Gray zone lymphoma, often presenting as large tumors in the mediastinum, is a type of lymphoma that is characterized by having cellular features of both classic Hodgkin's lymphoma Hodgkin lymphoma (HL) is a type of lymphoma in which cancer orig ...
.


Treatment

Multiagent chemotherapy is recommended, but the preferred regimen is controversial, as is consolidative
radiotherapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a treatment using ionizing radiation, generally provided as part of cancer therapy to either kill or control the growth of malignant cells. It is normally delivered by a linear particle ...
. Treatment commonly begins with either R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) or
DA-EPOCH-R EPOCH is an intensive chemotherapy regimen intended for treatment of aggressive non-Hodgkin lymphoma. It is often combined with rituximab. In this case it is called R-EPOCH or EPOCH-R. The R-EPOCH regimen consists of: # Rituximab: an anti-CD20 ...
(dose-adjusted etoposide, prednisolone, vincristine, cyclophosphamide, doxorubicin, rituximab). Other, more intense, regimens may be more effective.
PD-1 and PD-L1 inhibitors PD-1 inhibitors and PD-L1 inhibitors are a group of checkpoint inhibitor anticancer drugs that block the activity of PD-1 and PDL1 immune checkpoint proteins present on the surface of cells. Immune checkpoint inhibitors are emerging as a front-lin ...
can be used.
Radiation therapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...
may be added, especially if chemotherapy does not seem sufficient on its own. Radiation may cause other health problems later, such as
breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...
, and there is some debate about the best approach to it.
FDG-PET Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, re ...
scanning is not as useful for predicting treatment success in PMBCL as it is in other lymphomas.


Prognosis

Most people with PMBCL are successfully treated and survive for many years. However, if the initial treatment is unsuccessful, or if it returns, the long-term prognosis is worse. Relapses generally appear within 12 to 18 months after the completion of treatment.


Epidemiology

This lymphoma is most commonly seen in women between the age of 20 and 40.


See also

*
Diffuse large B-cell lymphoma Diffuse large B-cell lymphoma (DLBCL) is a cancer of B cells, a type of lymphocyte that is responsible for producing antibodies. It is the most common form of non-Hodgkin lymphoma among adults, with an annual incidence of 7–8 cases per 100,000 ...
*
Hodgkin lymphoma Hodgkin lymphoma (HL) is a type of lymphoma in which cancer originates from a specific type of white blood cell called lymphocytes, where multinucleated Reed–Sternberg cells (RS cells) are present in the lymph nodes. The condition was named a ...


References


External links

{{Lymphoid malignancy Lymphoma