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Thymoma and thymic carcinoma, explained side by side | CION Cancer Clinics
Thymoma and thymic carcinoma both start in the thymus, a small gland behind the breastbone. A thymoma usually grows slowly and often stays inside its covering, and surgery alone is often enough. Thymic carcinoma is rarer, grows faster and is more likely to spread, so other treatment is more often added. This page explains how to tell them apart on your report. CION Cancer Clinics’ surgical oncologists in Hyderabad can talk this through with you.
MI
Medically reviewed by Dr. Mohammed ImaduddinConsultant Surgical Oncologist · MBBS, MS (General Surgery), MCh (Surgical Oncology) · last reviewed September 2026, next review due September 2027
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On this page
- What is the difference between a thymoma and thymic carcinoma?
- How do the two usually compare?
- What do the letters A, AB, B and C mean?
- How are these tumours usually found?
- How does treatment usually unfold?
- Which other words will you see, and what do they mean?
- What do people often get wrong about thymus tumours?
- Common questions about thymoma and thymic carcinoma
The short answer
What is the difference between a thymoma and thymic carcinoma?
Both are tumours that start in the thymus, a small gland behind the breastbone. A thymoma usually grows slowly and often stays inside its covering. Thymic carcinoma is much rarer, grows faster and is more likely to spread beyond the chest.
Why the name on the report matters
The two are treated differently. With a thymoma, the operation is usually the main treatment, and many people need nothing more. With thymic carcinoma, surgery is still used when the tumour can be removed, but chemotherapy or radiotherapy are more often part of the plan. The follow-up is also different.
Why the answer is sometimes not known until after surgery
A CT scan can suggest which one it is, but it cannot confirm it. The final name comes from the pathologist looking at the tissue under a microscope. When a tumour looks small and contained, the surgeon may remove it whole without a biopsy first, so the exact type is only confirmed afterwards.
Other growths in the same space, such as lymphoma or a germ cell tumour, can look similar on a scan. Blood tests and sometimes a biopsy help rule them out.Side by side
How do the two usually compare?
Thymoma
Thymic carcinoma
Usually slow-growing
Usually faster-growing
Cells look fairly like normal thymus cells
Cells look clearly abnormal
Often linked with myasthenia gravis
Rarely linked with myasthenia gravis
Spread, when it happens, is mostly within the chest
More likely to reach lymph nodes, lungs, liver or bone
Surgery is often the only treatment needed
Surgery is often combined with other treatment
On the pathology report
What do the letters A, AB, B and C mean?
Pathologists use a World Health Organization system of letters to describe how the cells look. It helps the team plan, but it is only one part of the picture.
Type A and AB
Cells that look closest to normal. These tumours tend to grow slowly and are often found still inside their covering.
Type B1 and B2
Tumours with many immune cells mixed in. They are still thymomas, but more likely than type A to have grown into nearby tissue.
Often seen with
- Myasthenia gravis
Type B3
The thymoma type that tends to behave most aggressively. It is more likely to have spread into the lining of the lungs or heart, and radiotherapy after surgery is discussed more often.
Thymic carcinoma
Sometimes still called type C. The cells look like cancers found elsewhere in the body, and the report usually adds a sub-type such as squamous.
A type letter on its own says nothing certain about how things will go for you.Not sure whether this applies to you?
Ask an oncologistHow it comes to light
How are these tumours usually found?
Many are found by chance, on a chest X-ray or CT done for something else. Others show up because of pressure in the chest, or because of myasthenia gravis.
Symptoms from the tumour itself
A cough that does not settle, chest pain or tightness, breathlessness, or a hoarse voice. A large tumour can press on the big vein that drains the head and arms, causing swelling of the face, neck or arms. That swelling needs to be seen quickly.
Symptoms from the immune system
Thymomas can upset the immune system. The commonest result is myasthenia gravis: drooping eyelids, double vision, or weakness that gets worse as the day goes on. Less often, the bone marrow stops making enough red blood cells, or the body stops making enough antibodies, leading to repeated infections.
Who this page does not fit
If your report describes a thymic cyst or an enlarged but normal thymus, which is more common in young people, this comparison may not apply. Ask your doctor what the growth is thought to be.
The usual pathway
How does treatment usually unfold?
Scans and blood tests
A CT of the chest, sometimes an MRI or PET-CT. Blood tests check for other tumour types and for the antibody linked with myasthenia gravis.
Tumour board
Surgeons, medical and radiation oncologists decide together whether the tumour can be removed completely, and whether a biopsy is needed first.
Treatment before surgery, if needed
If the tumour is large or stuck to vital structures, chemotherapy may be given first to shrink it. This is more common with carcinoma.
The operation and the report
The surgeon removes the thymus and tumour. The report confirms the type, the stage and whether the edges are clear, which decides whether radiotherapy follows.
Follow-up for years
Regular CT scans continue long after treatment, because a thymoma can come back late. Carcinoma is usually checked more closely in the early years. Keep every report in one folder.
On your report
Which other words will you see, and what do they mean?
- Encapsulated
- The tumour is still inside its thin outer covering. This is generally a favourable finding.
- Invasive
- The tumour has grown through its covering into fat or nearby organs.
- Masaoka-Koga stage
- The staging system most used for these tumours. Staging describes how far the tumour has grown or spread, from stage I to stage IV.
- R0 resection
- The tumour was removed with no tumour cells seen at the edges. R1 or R2 means some was left behind, seen under the microscope or by eye.
- Pleural deposits
- Small spots of tumour on the lining of the lungs, sometimes found during the operation.
Commonly believed
What do people often get wrong about thymus tumours?
"A thymoma is harmless because it grows slowly."
It can still grow into nearby tissue and come back years later. That is why removing it completely, and keeping up the follow-up scans, matters even when it seems small.
"Every tumour must be biopsied before surgery."
Not always. When a thymoma looks small and contained, a needle through its covering can spill cells. Surgeons often remove it whole instead. A biopsy is usually done when the tumour looks unremovable or could be something else.
"Thymic carcinoma means nothing can be done."
It is more serious, but many people have surgery, chemotherapy or radiotherapy, alone or together. The plan depends on the stage and on your health, and your team will explain the realistic aims.
"Once the thymus is removed, myasthenia gravis will stop."
Weakness often improves slowly, over months or longer, but many people still need medicines. Some notice no change.
Questions we are asked
Common questions about thymoma and thymic carcinoma
Is a thymoma cancer?
Doctors treat every thymoma as a cancer that can spread, even though most grow slowly and stay in the chest. It is grouped with thymic carcinoma under thymic tumours. Calling it harmless is risky, because it can grow into nearby tissue or come back years later if not removed completely.
Can the type change from thymoma to carcinoma?
This is uncommon. A single tumour can occasionally contain areas of both, which is why the pathologist examines the whole removed tissue rather than one small piece. If a tumour comes back, it may be biopsied again to confirm what it is.
Why did my surgeon not do a biopsy first?
When a tumour looks like a small, contained thymoma that can be removed in one piece, a needle through its covering risks spreading cells along the track. Removing it whole gives the pathologist the full tumour. If the scan suggested lymphoma or a tumour that cannot be removed, a biopsy would usually come first.
Does the type tell us how long I have?
No single word on the report does that. Outlook depends on the type, the stage, whether the tumour was fully removed and your general health, taken together. Your oncologist can talk through what your own report means. This page cannot, and a figure found online will not describe you.
Will I need radiotherapy after surgery?
It depends on how far the tumour had grown and whether the edges were clear. Small contained thymomas that were fully removed often need nothing more. Radiotherapy is more often discussed for invasive thymomas, tumours with close or involved edges, and thymic carcinoma. The tumour board makes the recommendation.
Can these tumours be inherited?
Thymoma and thymic carcinoma are not generally thought of as inherited, and family members are not usually offered screening. Rarely, thymic tumours occur as part of an inherited condition affecting several glands. If there is an unusual family history, mention it to your doctor.
How often will I need scans afterwards?
More often in the first few years, then less often, but for a long time. Thymomas in particular can come back late, so follow-up often continues for many years. Your team will give you a schedule based on the type and stage of your tumour.
Is treatment covered by Aarogyasri or insurance?
Surgery, chemotherapy and radiotherapy for thymic tumours are usually covered when they are part of an approved plan. Aarogyasri, CGHS, ECHS, EHS and most cashless insurers are accepted, subject to their rules. Call the helpline with your card or policy details and the team will check your cover.
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Sources
- National Cancer Institute — Thymoma and Thymic Carcinoma Treatment (PDQ) - Patient Version
- American Cancer Society — Thymus Cancer
- Cancer.Net — Thymoma
- Cancer Research UK — Thymus gland cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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