carcinoma
Meaning of carcinoma: Naming a tumor a carcinoma answers only the first question, since the subtype and the organ decide nearly everything that follows.
Definition of carcinoma
Carcinoma is the broad category of cancer that develops from epithelial cells, the cells forming skin and lining the surfaces of internal organs, ducts and body cavities. Because epithelium covers so much of the body, carcinomas make up the large majority of cancers in adults, including most tumors of the lung, breast, colon and prostate.
What are the main subtypes?
| Subtype | Cell it arises from | Common sites |
|---|---|---|
| Adenocarcinoma | Gland-forming cells that secrete mucus or hormones | Colon, breast, prostate, pancreas, much of the lung |
| Squamous cell carcinoma | Flat, skin-like surface cells | Skin, mouth, throat, esophagus, cervix, part of the lung |
| Basal cell carcinoma | Basal cells at the base of the epidermis | Sun-exposed skin |
| Transitional cell carcinoma | The stretchable lining of the urinary tract | Bladder, ureter, kidney |
| Renal cell carcinoma | Cells lining the kidney tubules | Kidney |
Subtype is decided by how the cells appear under a microscope and by which proteins they carry, not by the organ alone. One organ can give rise to more than one subtype, and subtypes from the same organ can behave very differently, which is why a report names the subtype rather than stopping at the word carcinoma.
How does it differ from a sarcoma?
The two names divide solid tumors by tissue of origin. Carcinoma arises from epithelium, the sheets of cells that cover and line. Sarcoma arises from connective tissue, meaning bone, muscle, fat, cartilage, fibrous tissue and blood vessel walls. Carcinomas are far more common in adults, tend to appear later in life, and typically spread first to nearby lymph nodes. Sarcomas are rarer, make up a larger share of cancers in children and young adults, and more often spread through the bloodstream to the lungs. Leukemias and lymphomas belong to neither group, arising instead from blood-forming and immune cells.
What does in situ mean?
Epithelium rests on a thin sheet called the basement membrane. Carcinoma in situ describes cells that look fully malignant yet remain entirely above that sheet, so they have no access to blood or lymphatic vessels and cannot spread. Once cells break through it the tumor is invasive, and that single step is what makes distant spread possible. The distinction is made by examining tissue, since it depends on the relationship between the cells and a structure visible only under a microscope. It carries more weight than tumor size, because a large in situ lesion has a different outlook from a small invasive one.
Used in a sentence
Biopsy of the skin lesion confirmed a diagnosis of basal cell carcinoma.
Good to know
Carcinoma refers specifically to cancer of epithelial origin, distinguishing it from sarcoma, which arises from connective tissue such as bone, muscle or fat.
Word origin
Where “carcinoma” comes from
Formed from Greek karkinos, meaning crab, and -oma, meaning tumor, a name attributed to the crablike pattern of veins sometimes seen radiating from a tumor.