Thymoma Causes and Risk Factors

Thymoma is a rare cancer that originates in the thymus, a small gland located behind the breastbone that plays an important role in immune system development. Although the exact cause remains unclear and few well-established risk factors have been identified, thymoma occurs most frequently in middle-aged and older adults and is associated with certain autoimmune disorders, particularly myasthenia gravis.

According to the American Cancer Society, thymomas and related thymic tumors account for less than 1% of adult cancers. Despite their rarity, thymomas are the most common tumors of the thymus gland.

What causes thymoma? 

While no single cause has been identified, researchers continue to investigate the biological mechanisms that may contribute to thymoma development. These include:

• Acquired genetic mutations within thymic cells – DNA changes can disrupt the normal regulation of cell growth and division, allowing abnormal cells to multiply and form tumors.
• Abnormal immune system activity – Because thymoma frequently occurs alongside autoimmune disorders, researchers are studying whether immune system dysfunction may promote tumor development.

What are the risk factors for thymoma?

Researchers have identified a small number of characteristics and medical conditions that occur more frequently among people diagnosed with thymoma. These include:

• Increasing age – Thymoma is most often diagnosed in adults between the ages of 40 and 60, although it can occur at any age.
• Autoimmune disorders – Myasthenia gravis, an autoimmune condition that affects communication between nerves and muscles, occurs much more frequently among people with thymoma than in the general population.
• Pure red cell aplasia – This rare blood disorder, in which the bone marrow produces too few red blood cells, is associated with thymoma in a small percentage of patients.
• Hypogammaglobulinemia (Good syndrome) – A small percentage of people with thymoma develop Good syndrome, a rare acquired immune deficiency characterized by low antibody levels and an increased susceptibility to infections.

Which risk factors for thymoma are nonmodifiable?

Most recognized risk factors for thymoma cannot be changed. However, understanding these characteristics may help identify individuals who could benefit from closer medical evaluation should symptoms or associated conditions arise. Nonmodifiable risk factors for thymoma include:

• Age – Thymoma occurs most often in middle-aged and older adults, particularly those between the ages of 40 and 60.
• History of autoimmune disease – Certain autoimmune disorders, most notably myasthenia gravis, are frequently seen in people diagnosed with thymoma, although most individuals with these conditions will never develop thymoma.
• Certain blood and immune system disorders – Rare conditions such as pure red cell aplasia and Good syndrome are associated with thymoma.

Which risk factors for thymoma are modifiable?

Unlike many other cancers, thymoma has no well-established modifiable risk factors, and researchers have not identified any lifestyle changes that are known to prevent the condition. However, the following measures may help support earlier diagnosis and timely treatment:

• Routine medical care – Regular checkups and appropriate follow-up for new or persistent symptoms can help facilitate timely diagnosis and treatment when necessary.
• Prompt evaluation of unusual changes – Symptoms such as unexplained muscle weakness, chronic fatigue, chest discomfort, vocal hoarseness, breathing issues or difficulty swallowing should be evaluated by a healthcare provider right away, particularly in individuals with autoimmune conditions associated with thymoma.
• Management of autoimmune conditions – Although treating an underlying autoimmune disorder has not been shown to prevent thymoma, regular medical care may help identify related health concerns earlier.

Can thymoma be prevented?

Because the precise cause of thymoma remains unknown, there is currently no proven way to prevent this rare type of cancer. Although research continues, evidence to date has not identified any lifestyle or environmental modifications that are known to reduce the risk of developing thymoma. While prevention is not currently possible, the following measures may help support earlier diagnosis and timely treatment:

• Seeking a prompt medical evaluation for persistent symptoms – Unusual changes such as chest pain, shortness of breath, chronic coughing, unexplained muscle weakness or difficulty swallowing should be discussed with a physician.
• Following recommended care guidelines for autoimmune disorders – Individuals with myasthenia gravis or other autoimmune conditions should maintain regular follow-up with their healthcare team, as these disorders are closely linked to thymoma.
• Maintaining routine healthcare – Regular medical visits can provide opportunities to discuss new or changing symptoms and determine whether additional evaluation is needed.

Find the help you need for thymoma at Moffitt Cancer Center 

A thymoma diagnosis often raises questions about why the cancer developed and whether an underlying health condition may have contributed to its development. The multispecialty team in Moffitt's Thymoma Program provides comprehensive evaluations, advanced diagnostic testing, individualized treatment plans and expert guidance for patients with thymoma and other rare thoracic cancers.

If you have questions about thymoma causes, risk factors or treatment, you can request an appointment with a specialist at Moffitt by calling 1-888-663-3488 or submitting a new patient registration form online. We do not require referrals.