Thymic Carcinoma

 

Thymic (Thymus) Carcinoma

 

The thymus gland is a small gland lying anterior to the thoracic cavity and beneath the breastbone (sternum). It has two parts: the outer cortex and the inner medulla. A capsule covers the cortex. The main function of this gland is selection and maturation of T-cells, which has an important role in the cell-mediated immunity. Cancer in thymus can be of several types.

  1. Epidemiology Thymoma and thymic carcinoma are rare diseases. There are only around 400 tumors diagnosed per year in the United States. These tumors come from epithelial cells in the thymus.It is equally frequent in males and females. The risk of this tumor increases with age.

    Thymomas can be benign or cancerous (carcinomas). Some people with thymomas experience what is called the paraneoplastic syndrome.

    Types of thymic cancer

    Many classifications systems have been developed to describe the types of thymus cancer. Recently, WHO has proposed a classification system, according to which these are the following types based on what they look like under a microscope:

    • Type A thymoma
    • Type AB thymoma
    • Type B1 thymoma
    • Type B2 thymoma
    • Type B3 thymoma
    • Thymic carcinoma (also called Type C thymoma)

    Symptoms of thymic cancer

    • Shortness of breath (breathing problems)
    • Pain in the chest
    • Coughing
    • Difficulty swallowing
    • Weight loss/loss of appetite
    • Swollen face
    • Headache

    Symptoms depend on many factors in case of thymic cancer. Almost 40 % patients do not show any symptom.

    Patients who develop a paraneoplastic syndrome can have autoimmune disorders like myasthenia gravis, red cell aplasia, and hypogammaglobulinemia, and others, all related to the thymus cancer.

    Causes and Risk factors of thymic carcinoma

    The cause of thymic cancer is not known. Risk goes up with age.

    Diagnosis

    A thymoma may be diagnosed because a person has developed myasthenia gravis, red cell aplasia, or other autoimmune disease.

    Physical exam and patient’s history: Doctors check for abnormalities by examining the general health of the patient. Lumps can be felt, if there is any. A patient’s history of previous diseases also helps the doctor to plan what tests should be performed and the type of treatment to be given to the patient.

    Chest x-ray: The chest x-ray provides images of the organs inside the chest. Any abnormalities in the thymus can be diagnosed from these images.

    CT scan (CAT scan): The CT scan can detect small tumors in the thymus. The procedure involves imaging with the help of x-rays and a computer. A dye is injected in the veins of swallowed to give contrast to the images.

    MRI (magnetic resonance imaging): The MRI also gives images of the organs but uses a magnet, radio waves, and a computer to make the images.

    PET scan (positron emission tomography scan): The PET scan is an important procedure to detect cancers. This process requires the injection of radioactive glucose in the vein. The scanner then gives images of the whole body. Places in the body where glucose consumption is more than normal (characteristic of cancer cells) shows higher radioactive accumulation and appears brighter in the scans.

    Biopsy

    Tissues or cells obtained from biopsy can be studied under the microscope in laboratory. The CT scan is used to guide the needle to the affected site. However, for thymus cancer, biopsies are not usually done, since there is a chance that the cancer may spread after the biopsy.

    Treatment

    Surgery: Surgery is the preferred treatment for thymus cancer at an early stage. In most cases, the gland is completely removed and this type of surgery is called thymectomy. Parts of nearby organs to which the cancer has spread is also removed during surgery. For stage III and stage IV thymus cancer, surgery may or may not be performed. Some doctors suggest surgery to remove as much tumors possible (debulking), while others prefer radiation therapy and chemotherapy in such cases.

    Radiation therapy: Radiation therapy is not as effective as surgery for thymic carcinoma. High energy x-rays are used to kill the cancer cells in the thymus. This can be done in two ways:

    External radiation therapy: Radiation is given by a machine from outside the body at the affected region.

    Internal radiation therapy: Radioactive substance sealed in a needle or wire is placed near the thymus. Radiation emitted from this radioactive substance kills the cancer cells.

    Radiation therapy may be given to reduce the size of tumors before surgery. It may also be used as an adjuvant therapy after surgery to remove the cancer cells, which could not be removed. The radiation therapy works better in combination with chemotherapy.

    Chemotherapy: Chemotherapy is the use of drugs to treat cancer. It can be swallowed or administered through veins. It can also be specifically directed at the cancer affected region. For stage I and II, chemotherapy can be given to patients as neo-adjuvant therapy (before the surgery) or as adjuvant therapy (after the surgery). For advanced stages, especially in cases where surgery cannot be done, chemotherapy in combination with radiation therapy is the main treatment. Several drugs such as cisplatin, carboplatin, doxorubicin, cyclophosphamide, ifosfamide and many others are used for thymus cancer.

    Staging

    The Masaoka staging system is mostly followed to stage cancer in the thymus gland. The stages are as follows:

    Stage I

    Cancer in the thymus has not spread in the capsule (outer covering of the gland).

    Stage IIA

    The cancer has spread into the capsule of the gland.

    Stage IIB

    The cancer has grown into nearby fatty tissues, mediastinal pleura of the lungs and/or the pericardium of the heart.

    Stage III

    The cancer spreads in the nearby tissues and organs including the pericardium of heart, lungs and blood vessels connected to the heart.

    Stage IVA

    The cancer has spread extensively in the pleura of the lungs and the pericardium of the heart.

    Stage IVB

    The cancer has metastasized to many other distant organs such as liver and kidneys.

    Prognosis

    The stage of the thymic cancer at the time of diagnosis is the most important factor that influences prognosis. If the tumor is localized within the thymus then the chance of survival is around 88 %. This can be cured by surgery and radiation therapy.

    But, if the cancer spreads to nearby and distant organs, then the chance of survival decreases to 74 % and 41 % respectively. This indicates that early diagnosis is important. Prognosis is also affected by other factors such as size of the tumor at the time of diagnosis and the general health of the patient.

    References

    1. Huang J, Detterbeck FC, Wang Z, Loehrer PJ Sr. (2011) Standard outcome measures for thymic malignancies. J Thorac Oncol.;6 (7 Suppl ):S1691-7.
    2. Rajan A, Giaccone G. (2008) Treatment of advanced thymoma and thymic carcinoma.
    3. Curr Treat Options Oncol.;9(4-6):277-87.
    4. Ströbel P, Hohenberger P, Marx A. (2010) Thymoma and thymic carcinoma: molecular pathology and targeted therapy. J Thorac Oncol.;5(10 Suppl 4):S286-90.
    5. Venuta F, Anile M, Diso D, Vitolo D, Rendina EA, De Giacomo T, Francioni F, Coloni GF. (2010) Thymoma and thymic carcinoma. Eur J Cardiothorac Surg.;37(1):13-25.
    6. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.