What Is Thymoma and Thymic Cancer?
Thymoma is a tumor of the thymus gland or thymic tissue—a small organ located in the upper portion of your chest (also called mediastinum), extending from the base of the throat to the front of the heart. The thymus gland is part of your immune system, and secretes hormones that enable T-Cells (disease-fighting cells) to function against disease-causing organisms.
Thymomas are malignant tumors that arise in the thymus gland, typically in the anterior mediastinum. Although considered malignant, most thymomas grow slowly and tend to spread only locally, by “seeding” cells into surrounding tissues and spaces such as the pleural space (the space surrounding each lung). There is therefore often a very good chance of curing thymomas by either surgery alone or surgery followed by radiation. We often proceed to remove these localized tumors without even the need for a preliminary biopsy.
The thymus is most active in children and becomes less active with age, so removal of the thymus has no ill effects in adults. Most thymomas have a relatively high rate of cure with either surgery alone, or surgery plus radiation therapy. Some more advanced thymic tumors are categorized as “thymic cancer” rather than as “thymoma.” These tend to be more aggressive than thymomas, and even if they have not spread beyond the mediastinum, they are often treated with combination therapy, including chemotherapy, radiation, and surgery.
Thymus cancers are rare, accounting for about 0.2% to 1.5% of all cancers, and can be difficult to diagnose.
Thymoma and thymic cancer program highlights
Stanford thoracic surgeons evaluate and treat a high volume and wide variety of mediastinal diseases. Since many of these lesions are benign, minimally invasive approaches, which allow for less discomfort and faster recovery, can often be utilized. As in all areas of thoracic surgery, Stanford thoracic surgeons have sub-specialty training in the surgical management of mediastinal tumors and diseases. They have far more experience with these relatively rare diseases than general surgeons and even cardiothoracic surgeons at surrounding community hospitals. For example, in the past year alone, Stanford thoracic surgeons have removed or biopsied 204 mediastinal masses—a very large volume of these cases for a single institution.
- Weekly multispecialty thoracic tumor board to review complex cases and develop optimal treatment plans
- Advanced diagnostic capabilities, including combined staging/tumor assessment, PET-CT scan
- Multispecialty treatment for locally advanced thymoma and thymic cancer
- Surgical expertise, including doctors with extensive experience performing thymectomy (thymus removal) and minimally invasive thymic surgery for smaller tumors. Complete resection is one of the most important determinants of cure and survival rates in patients with thymic tumors. Our surgeons are experienced in all advanced resection and reconstruction techniques, including superior vena cava reconstruction, required to give the greatest chance of cure for thymic malignancies.
- Clinical trials of potential new treatments for thymoma
Types of Thymoma and Thymic Cancer
The thymus has different types of cells, each of which can develop into different types of thymoma or cancer:
- Epithelial cells give the thymus its structure and shape. Thymomas and thymic carcinomasdevelop from these cells.
- Lymphocytes make up most of the rest of the thymus. Whether in the thymus or in other parts of the body, these immune system cells can develop into cancers called Hodgkin disease and non-Hodgkin lymphomas.
- Kulchitsky cells, or neuroendocrine cells, are much less common cells that normally release certain hormones. These cells can give rise to cancers called neuroendocrine (formerly called carcinoid) tumors.
Doctors can tell the different thymic cancers apart by how they look under the microscope and by the results of other lab tests done on tissue samples.
Physical exam provides information about possible signs of thymic cancer and other health problems. Thymomas are often diagnosed by recognizing the signs and symptoms associated with myasthenia gravis, hypogammaglobulinemia or red cell aplasia.
A chest X-ray is used to look for any mass or spot in the chest/thymus area.
Computed Tomography Scan (CT Scan)
Combined PET/CT scan
What Is Positron Emission Tomography (PET) Scan?
Positron emission tomography, also called PET imaging or a PET scan, is a type of nuclear medicine imaging. A PET scan measures important body functions, such as blood flow, oxygen use, and sugar (glucose) metabolism, to help doctors evaluate how well organs and tissues are functioning.
PET is a powerful diagnostic test that is having a major impact on the diagnosis and treatment of disease. A PET scan (positron emission tomography scan) monitors the biochemical functioning of cells by detecting how they process certain compounds, such as glucose (sugar). PET can detect extremely small cancerous tumors, subtle changes of the brain and heart, and give doctors important early information about heart disease and many neurological disorders, like Alzheimer’s.
Most common medical tests, like CT and MRI scans, only show details about the structure of your body. PET scans give doctors images of function throughout the entire body, uncovering abnormalities that might otherwise go undetected. This allows doctors to treat these diseases earlier and more accurately. A PET scan puts time on your side. The earlier the diagnosis, the better the chance for treatment.
For example, a PET scan is the most accurate, non-invasive way to tell whether or not a tumor is benign or malignant, sparing patients expensive, often painful diagnostic surgeries and suggesting treatment options earlier in the course of the disease. Although cancer spreads silently in the body, PET can inspect all organs of the body for cancer in a single examination.
Today, most PET scans are performed on instruments that are combined PET and CT scanners. The combined PET/CT scans provide images that pinpoint the location of abnormal metabolic activity within the body. The combined scans have been shown to provide more accurate diagnoses than the two scans performed separately.
About nuclear medicine
Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose or treat a variety of diseases, including many types of cancers, heart disease, and certain other abnormalities within the body. Depending on the type of nuclear medicine exam you are undergoing, the radiotracer is either injected into a vein, swallowed or inhaled as a gas and eventually accumulates in the organ or area of your body being examined, where it gives off energy in the form of gamma rays. This energy is detected by a device called a gamma camera, a PET scanner and/or probe.
During a needle biopsy, a thin, hollow needle is guided into the mass while the lungs are being viewed on a fluoroscopy or CT scan, and a sample of the mass is removed and evaluated in the pathology laboratory under a microscope.
In many cases, if your doctor believes that you have thymoma (based on CT findings and lab tests, especially if you also have a paraneoplastic syndrome) and it can be removed with surgery, he or she may operate without any biopsy. This can both provide enough of a sample for a diagnosis and treat the tumor at the same time. The specimen is sent to the lab after surgery to confirm the diagnosis.
Stage 1 thymoma (I)
Completely encapsulated tumor, without tumor invasion into the capsule
Stage 2 thymoma (II)
Tumor invasion into fatty/thymic tissue surrounding the tumor or microscopic invasion into the capsule
Stage 3 thymoma (III)
Tumor invasion into organs surrounding the thymus
Stage 4A thymoma (IVA)
Tumor implants in the pleura or pericardium (the linings of the lungs or heart)
Stage 4B thymoma (IVB)
Spread to lymph nodes or via bloodstream to distant organs
World Health Organization (WHO) system
B1, B2, B3
C Thymic Carcinoma
Cure rates for Masaoka stage I tumors are 90-95%; stage II 85-90%; stage III 50-70%; stage IV 20-50%. WHO type A and AB tumors within each of these Masaoka stages appear to have cure rates at the higher end of the range, while those with type B tumors will fall at the lower end of the cure range. Type C tumors—thymic carcinoma—have the worst prognosis.