cancer
Meaning of cancer: Not one disease but hundreds, grouped by the tissue they start in, and it is invasion and spread that separate them from harmless growths.
Definition of cancer
Cancer is a group of diseases in which cells lose the controls on their own growth, divide when they should not and ignore the signals that normally tell a damaged cell to die. The resulting mass can push into neighboring tissue and shed cells that travel through blood or lymph to grow elsewhere, which is called metastasis.
What are the main groups?
| Group | Starts in |
|---|---|
| Carcinoma | Cells lining or covering surfaces: skin, gut, lung airways, breast ducts, glands |
| Sarcoma | Bone, muscle, fat, cartilage and other connective tissue |
| Leukemia | Blood-forming tissue in the bone marrow, circulating rather than forming a lump |
| Lymphoma | Lymphocytes in lymph nodes and lymphatic tissue |
These four cover most cases but not all of them. Myeloma arises from plasma cells in the bone marrow, melanoma from the pigment cells of the skin, germ cell tumors from the cells that form eggs and sperm, and tumors of the brain and spinal cord from the supporting cells of the nervous system. Carcinoma is the largest group by far, and sarcoma, which grows from connective tissue, is among the least common.
What separates cancer from a harmless growth?
| Benign | Malignant | |
|---|---|---|
| Border | Pushes tissue aside, often within a capsule | Invades and infiltrates surrounding tissue |
| Spread | Stays where it started | Can travel to distant sites |
| Growth | Usually slow, may stop | Continues, often accelerating |
| Cell appearance | Resembles the tissue of origin | Increasingly disordered and abnormal |
A benign growth can still cause serious trouble by pressing on something important, so harmless is relative to its position, but it does not invade or metastasize.
Why does the type of cancer matter so much?
Cancers are named for where they began, not where they are found. A breast cancer that has spread to bone remains a breast cancer, made of breast cells, and behaves and responds like one rather than like a bone cancer. This is why identifying the tissue of origin is the first task, and why a cancer whose origin cannot be traced is handled as its own difficult category. Beyond origin, the grade describes how abnormal the cells look, the stage describes how far the disease has traveled, and molecular features describe which faults are driving it. Those four together, rather than the single word cancer, determine what happens next.
Also known as
Used in a sentence
Tissue obtained during the biopsy was examined to determine whether the growth represented cancer.
Good to know
Not every abnormal growth is cancer, since a growth described as benign lacks the ability to invade nearby tissue or spread elsewhere, which distinguishes it from a malignant growth.
Word origin
Where “cancer” comes from
From Latin cancer, meaning crab, translating the Greek karkinos, a name traditionally attributed to the crablike appearance of the swollen veins around some tumors.