Primary mediastinal large B-cell lymphoma (PMBCL) — sometimes called primary thymic mediastinal lymphoma — is a cancer that forms from cells of the immune system called B lymphocytes, or B cells. It is a type of non-Hodgkin lymphoma (NHL), one of the major categories of lymphoma. PMBCL primarily affects young adults, mostly women, but it can also affect children. It is a relatively rare cancer and makes up only 2 percent to 4 percent of all non-Hodgkin lymphomas.
PMBCL causes a tumor to form in a space between the lungs known as the mediastinum. The majority of people with PMBCL have a tumor greater than 10 centimeters in diameter — known as bulky disease — and are diagnosed in the early stages of disease, when it is still localized. Although PMBCL is a form of NHL, the condition’s cancer cells resemble those found in classical Hodgkin lymphoma when analyzed under a microscope. PMBCL also shares features with diffuse large B-cell lymphoma (DLBCL). PMBCL may be considered a subtype of DLBCL.
Most signs and symptoms of PMBCL are caused by the mediastinal mass compressing nearby organs. They may include:
Enlarged lymph nodes, a common feature of non-Hodgkin lymphoma, are typically seen only within the mediastinum.
Diagnosing PMBCL involves many of the same tests used for diffuse large B-cell lymphoma.
A lymph node biopsy involves your doctor removing lymph node tissue from the mediastinum and examining it for the presence of cancer cells. The biopsy can be a surgical biopsy, which entails removing an entire lymph node from the body, or a needle biopsy, the removal of a portion of a lymph node.
A doctor may obtain a bone marrow sample via bone marrow biopsy or aspiration. A bone marrow biopsy entails removing a small tissue sample from the bone marrow. A bone marrow aspiration involves taking a sample of liquid from the bone marrow.
CT scans, as well as scans combining positron emission tomography (PET) with CT — called PET-CT — are used to image the tissues within the body. CT or PET-CT can be used to image the characteristic mediastinal mass and pleural effusion (the accumulation of fluid around the lungs) that is common in PMBCL.
Chemotherapy is the standard initial treatment approach for PMBCL. Combinations of chemotherapy drugs are often used for certain treatment regimens, generally with a drug called Rituxan (rituximab). Rituximab is an antibody that can target PMBCL cancer cells because it recognizes a specific molecule called CD20 on their surface.
Chemotherapy regimens commonly used to treat PMBCL include:
Chemotherapy — with or without the addition of rituximab — is often effective at treating PMBCL. However, some people have cancer that is refractory (doesn’t respond well to treatment) or that has relapsed (come back after a period of time). In such cases, a stem cell transplant may be recommended. A stem cell transplant allows a person undergoing treatment to tolerate high-dose chemotherapy by replacing the damaged cells of the bone marrow with healthy cells. A transplant can be done using stem cells from a healthy donor, in an allogeneic stem cell transplantation, or using stem cells from the person’s own body, in an autologous stem cell transplantation.
People diagnosed with PMBCL may participate in clinical trials to identify potential new therapies. One new type of treatment that is currently being investigated is called chimeric antigen receptor (CAR) T-cell therapy. CAR T-cell therapy involves removing white blood cells called T cells from the person with cancer and then altering the cells to contain CARs on the surface. The modified cells are then put back into the person, where the cells can recognize molecules on the cancer cells and target the cancer cells for destruction.
The prognosis, or outlook, for PMBCL is generally favorable. The majority of people respond well to treatment and many are cured. The five-year survival rate is 80 percent to 90 percent. However, some people experience refractory or relapsed disease that is much more difficult to treat, leading to poor outcomes. Ongoing research to identify more effective treatments is important for improving the outcomes of people living with PMBCL.
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