thymic carcinoma
Meaning of thymic carcinoma: A cancer of the gland behind the breastbone that behaves nothing like the far commoner tumor it was once filed under.
Definition of thymic carcinoma
Thymic carcinoma is a rare and aggressive cancer arising in the thymus, the gland behind the breastbone that trains immune cells during childhood. Its cells look plainly malignant under the microscope, unlike those of the much commoner thymoma, and it invades neighboring structures and spreads to distant organs far more readily. Squamous cell carcinoma is the commonest of its several subtypes.
Is it a kind of thymoma?
No, and older sources calling it type C thymoma are quoting a classification that has since been abandoned. The two are now handled as separate diseases that happen to arise in the same thymus. A thymoma keeps recognizable features of normal thymus tissue and shelters a population of immature immune cells among its tumor cells. A thymic carcinoma has lost both, looks like a carcinoma from anywhere else in the body, and is identified by staining patterns thymoma does not show. The old label mattered because type C implies the severe end of one spectrum, when what is actually present is a different disease taking a different course.
How do the two compare?
| Feature | Thymoma | Thymic carcinoma |
|---|---|---|
| Appearance of the cells | Still resembles thymus tissue | Plainly malignant |
| Immature immune cells within | Present | Absent |
| Accompanying autoimmune disease | Common | Rare |
| Growth pattern | Often slow and contained | Invades early, spreads more often |
| Outlook | Frequently good | Considerably worse |
Why does the autoimmune difference matter?
Because it changes how each tumor comes to light. A thymoma is often discovered because a person develops muscle weakness with drooping eyelids and double vision, or some other disorder in which the immune system attacks the body's own tissue, and the scan ordered to investigate that reveals the mass. The gland's normal job is teaching immune cells to tell self from foreign, and a tumor built from that tissue disrupts the teaching. A thymic carcinoma has lost the tissue capable of doing so, so it rarely produces those syndromes and announces itself instead by pressure: chest pain, cough, breathlessness, or a swollen face and neck when the large vein draining the head is squeezed. Subtypes are named for the cells they resemble, and squamous cell carcinoma is much the commonest, the same tumor type seen in skin and airways.
Also known as
Used in a sentence
Thymic carcinoma was diagnosed after resection of an anterior mediastinal mass.
Good to know
Thymic carcinoma is no longer classified as a form of thymoma, and unlike thymoma it is only rarely accompanied by myasthenia gravis or other autoimmune conditions, which is often the first clue distinguishing the two.
Word origin
Where “thymic carcinoma” comes from
Carcinoma comes from the Greek karkinos, meaning crab, an old description of the way a spreading tumor grips the tissue around it, with the ending -oma marking a growth.