Thymic tumors: thymoma, thymic carcinoma

Introduction

The thymus is a small organ that lies in the upper chest above the heart and under the breastbone. It is part of the lymphatic system and makes white blood cells (lymphocytes), that protect the body against infections.

Thymoma and thymic carcinoma are two types of rare diseases in which malignant (cancer) cells form on the outside surface of the thymus.

Although thymoma and thymic carcinoma arise from the same type of cell, they have different features:

• Thymoma: tumor cells in a thymoma look like the normal cells of the thymus, grow slowly, and rarely spread beyond the thymus.
• Thymic carcinoma: tumor cells look very different from the normal cells of the thymus, grow more quickly, and have usually spread to other parts of the body at diagnosis.

Thymoma and myasthenia gravis

Thymoma is linked with myasthenia gravis and other autoimmune diseases (the immune system attacks healthy tissue and organs).

Autoimmune diseases linked with thymoma include:

• Myasthenia gravis (the most common autoimmune disease linked with thymoma).
• Thymoma-associated hypogammaglobulinemia.
• Thymoma-associated autoimmune pure red cell aplasia.
• Polymyositis.
• Lupus erythematosus.
• Rheumatoid arthritis.
• Thyroiditis.
• Sjögren syndrome.

 

Signs and symptoms

Most patients do not have signs or symptoms at diagnosis. Thymoma and thymic carcinoma may be found during a routine chest x-ray. Check with your doctor if you have any of the following:

• A cough that doesn't go away.
• Chest pain.
• Shortness of breath.
• Swelling in the face, neck, upper body, or arms.

Diagnosis

• Medical history and physical examination: A history of the patient’s past illnesses and an exam of the body to check general signs of health, including checking for signs of disease will be obtained.
• Chest x-ray: An x-ray of the organs and bones inside the chest.
• Computed tomography (CT scan): A procedure that makes a series of detailed pictures of areas inside the body. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein to help the organs show up more clearly.
• Positron-emission tomography scan (PET scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose is injected into a vein. The PET scanner takes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.
• Magnetic resonance imaging (MRI): A procedure that uses a magnet, radio waves and a computer to make a series of detailed pictures of areas inside the body.
• Biopsy: Sometimes a wide needle is used to take a tissue sample, this is called a core biopsy. A pathologist will review the sample under a microscope to check for cancer.

Staging

Staging is the process used to find out if cancer has spread from the thymus to other parts of the body. The tests’ results and findings made during surgery are used to determine the stage of the disease. It is important to know the stage in order to plan the most appropriated treatment.

The following stages are used for thymoma:

• Stage I: cancer is found only within the thymus and all cancer cells are inside the capsule that surrounds the thymus.
• Stage II: cancer has spread through the capsule and into the fat around the thymus or into the lining cells of the chest cavity.  
• Stage III: cancer has spread to nearby organs in the chest (lung, the sac around the heart or large blood vessels that carry blood to the heart).
• Stage IV: It is divided into stage IVA and stage IVB, depending on where the cancer has spread.
  • In stage IVA: cancer has spread widely around the lungs or heart.
  • In stage IVB: cancer has spread to the blood or lymphatic system.

Thymic carcinomas have usually spread to other parts of the body when the cancer is found. The staging system used for thymomas is sometimes used for thymic carcinomas.

Treatment

There are different types of treatment for patients with thymoma and thymic carcinoma.

Up to five types of standard treatment are used:

• Surgery
• Radiation therapy
• Chemotherapy
• Hormone therapy
• Targeted therapy
• New types of treatment are being tested in clinical trials: Immunotherapy

Follow-up tests may be needed.

Treatment options for thymoma

Stage I Thymoma: Surgery.

Stage II Thymoma: Surgery followed by radiation therapy.

Stage III and stage IV Thymoma:

• If the tumour may be completely removed with surgery, treatment options include the following:
  • Surgery followed by radiation therapy.
  • Neoadjuvant chemotherapy followed by surgery with or without radiation therapy.
• If the tumour cannot be completely removed with surgery, treatment options include the following:
  • Neoadjuvant chemotherapy followed by surgery and radiation therapy.
  • Chemotherapy followed by radiation therapy.
  • Chemotherapy.

Treatment options for thymic carcinoma

The treatment for thymic carcinoma that may be completely removed with surgery includes the following:

• Surgery followed by radiation therapy with or without chemotherapy.

 

The treatment for thymic carcinoma that cannot be completely removed with surgery includes the following:

• Chemotherapy followed by surgery to remove completely or part of the tumour and radiation therapy.
• Chemotherapy with radiation therapy.
• Chemotherapy.
• Radiation therapy.

Treatment options for recurrent thymoma and thymic carcinoma

In case the tumor reappears after a first line of treatment, oncologist will discuss (probably in a multidisciplinary tumor board) other possible alternative treatments as:

• Chemotherapy
• Hormone therapy (octreotide) with or without prednisone.
• Targeted therapy.
• Surgery.
• Radiation therapy.
• Immune checkpoint inhibitor therapy (pembrolizumab).

 

For more information on thymic conditions, please, visit https://itmig.org/about-thymoma/.