What is a mediastinal lymphoma?
Mediastinal lymphoma is a rare type of cancer. More popularly known as primary mediastinal B-cell lymphoma (or PMBL), it arises in a specialized organ of the immune system called the thymus. Mediastinal lymphoma or PMBL mostly affects young adults. It is a sub-type of diffuse large B-cell lymphomas (DLBC), which are the most common and aggressive types of all the lymphomas.
Lymphomas are the cancers of the lymphocytes, which are a type of immune cells. Both diffuse large B-cell lymphomas and primary mediastinal B-cell lymphomas affect B-lymphocytes of the immune system; however, the thymic mediastinal lymphoma has a better prognosis. Primary mediastinal B-cell lymphomas may also resemble another type of lymphoma, Hodgkin lymphoma, in their characteristics.
How common is a mediastinal lymphoma?
Primary mediastinal B-cell lymphoma make up about 5% of all lymphomas. Majority of the patients with mediastinal lymphomas are young adults in their 30s. It is slightly more common in females than in males, which is unlike other lymphomas where more males are affected than females. Mediastinal lymphoma has an aggressive course and, if left untreated, it can cause death. Appropriate treatment, however, shows good prognosis and 50& to 80% cases can be cured.
Thymus is located in the mediastinum, which is the part of the body inside the chest, behind the breast bone and between the lung cavities. The rapidly growing primary mediastinal B-cell lymphoma presents as a large tumor mass in the front part of mediastinum. The location of these cancers gives the condition its name – mediastinal lymphoma.
Effects of Mediastinal Lymphoma
Due to the presence of primary mediastinal B-cell lymphoma, the organs in the thoracic cavity are compressed. These cancers in the chest area may also compress the superior vena cava, the second largest vein carrying blood from the upper body to the heart. Compression of superior vena cava produces symptoms of superior vena cava syndrome.
Mediastinal lymphoma can invade the lungs, lung cavities, and heart cavity. In recurrent cases of mediastinal lymphomas, the cancer may spread to the kidneys, the liver, or the central nervous system (brain and spinal cord). Compression of nearby organs and spread to other sites may all contribute to the signs and symptoms.
Signs and Symptoms
Mediastinal lymphomas may present with the some of the following symptoms:
- Palpable mass in the supraclavicular (above the clavicle or collar bone) area
- Symptoms of superior vena cava syndrome is common
- Symptoms of phrenic nerve palsy
- Difficulty swallowing
- Hoarseness in voice
- Breast swelling (in females)
- Night sweats
- Weight loss
Causes of Mediastinal Lymphoma
The cause of development of mediastinal lymphoma is unknown. There is some suggestion that it may be associated with genetic factors.
Tests and Diagnosis
While diagnosing, it is important to differentiate between mediastinal lymphoma and other types of cancers (like acute lymphoblastic leukemia or ALL, tumors of germ cells, carcinoma, hodgkin disease, malignant anaplastic lymphoma, lymphoblastic lymphoma, and thymoma). Correct diagnosis improves the outcome of the treatment. The following tests can be performed to diagnose mediastinal lymphoma:
- Lab tests: Blood samples are checked for complete blood cell count, number of platelets, electrolyte levels, lactic dehydrogenase (LDH) levels, beta-2 microglobulin levels, and liver function tests.
- Imaging studies: Chest x-rays can detect a large mass in the thorax. A computed tomography (CT) or a positron emission tomography (PET) scan can invasion of lung and heart cavities and chest wall. It can also show the invasion of the liver, kidneys, and lymph nodes in recurrent cases. A gallium scan using radioactive gallium gives accurate diagnosis.
- Biopsy: Bone marrow aspiration and biopsy of a lymph node or of the mediastinal mass may be performed to stage the cancer.
- Histological tests: Slices of the biopsy samples can be stained with different dyes and viewed under the microscope to show diffuse and large B cells.
Cancer Treatment and Stem Cells
Six cycles of chemotherapy is given to the patients of primary mediastinal B-cell lymphoma, and the drugs are given every 3 weeks. A combination of chemotherapeutic drugs is given to the patients. The drugs usually contain corticosteroids (like prednisone), an alkylating agent (like cyclophosphamide), an anthracycline antiobiotic (like doxorubicin), and a vinca alkaloid (like vincristine).
Monoclonal antibody rituximab has shown good efficacy against large B-cell lymphoma. Combination of rituximab with other drugs has minimal additive side effects. Recombinant cytokines (like filgrastim, pegfilgrastim, or sargramostim) are given to hasten the recovery of blood counts and to improve cure rates.
Involved-field radiation is given to the mediastinum of some patients after completion of the chemotherapy. These two steps of this combined modality therapy are done at separate times.
Stem cell transplantation
Autologous (self) stem cell transplantation is recommended to some patients after the completion of combination chemotherapy. In autologous transplantation, stem cells are collected, high doses of chemotherapy are given, and the stem cells are re-infused. Patients are required to take cytokines and antibiotics. Stem cell transplantation is also recommended to patients with recurrent mediastital lymphomas.
Infections can be managed with the help of quinolone antibiotics (like levofloxacin or ofloxacin). Preventative anti-bacterial drugs (quinolone), anti-fungals (fluconazole), and anti-viral medicines (acyclovir, valacyclovir) are usually given to the patients.
The chemotherapeutic drugs given to treat mediastital lymphomas have various adverse effects. Nausea and vomiting are common side effects. However, these symptoms can be tolerated with the use of appropriate anti-emetic drugs. Hair loss during the treatment is common in most patients but hairs grow back after the completion of treatment. Chemotherapy may also damage peripheral nerves, resulting in symptoms of mild peripheral neuropathy (like numbness in fingertips and toes). Bone marrow suppression, fatigue, infection, and reduction in numbers of RBCs, WBCs, and platelet are common after every treatment cycle.
Cardiac toxicity due to chemotherapy is seen in rare cases. Cardiac toxicity from anthracyclines is more common of such cases. However, the use of cardioprotectant agents is not recommended as they might affect the efficacy of chemotherapy. Radiation therapy may cause sudden adverse effects like redness and rashes of the skin and, sometimes, radiation-induced injury and inflammation in the lungs. Chemotherapeutics may also cause late side-effects like decreased fertility, higher risks of cancers and leukemia in radiation fields. If heart is exposed to radiation, it may also result in coronary artery disease.
Prognosis of patients receiving timely treatment is good. Initial treatment can cure 50% to 80% of all patients with mediastinal lymphoma. In case of recurrent mediastital lymphomas, the recurrences occur in the first year after diagnosis. For such patients and for those who do not respond to the initial treatment, high-dose chemotherapy and autologous stem cell transplantation is recommended. These options achieve long-term disease-free periods in more than 35% of these patients.