These words refer to the development of abnormal cells, usually in tissue masses, in a living organism. Neoplasm is the most comprehensive term for any such development, whether malignant or benign, small or large, active or dormant, temporary or permanent. Usually the word refers to a tissue mass: neoplasms of the cervix, uterus and ovaries. But the word can also refer to the abnormal production of circulating cells.

• Leukaemia is a malignant neoplasm of the blood; Hodgkin’s disease is a comparable neoplasm of the lymph cells.

Tumour is the medical term and growth the layman’s term for any neoplasm that takes the form of a compact tissue mass. Growth is, of course, vague in its application to any swelling or non-functional mass: a growth on his vocal cords. Tumour refers specifically to a circumscribed growth that is non-inflammatory, useless to the body, and continues to develop independently of the normal rate for the tissue in which it arises: a breast tumour ; a lung tumour . Tumour , like growth and neoplasm , need not indicate malignancy. Cyst refers specifically to an abnormal but not necessarily malignant sac containing fluid or semi-solid material; a cyst can result from the clogging of a duct and is often temporary or minor in nature: a sebaceous cyst .

The remaining words all refer strictly to malignant neoplasms. Cancer indicates a disease in which cells stop functioning normally, become destructive of other cells and multiply rapidly. Most often this cellular malfunction is initially localized, becoming apparent when it produces a tumour , and then at last spreading unpredictably from one part of the body to another. Unless it is interrupted by surgery, X-ray treatment or drugs, the result is usually fatal: lung cancer ; stomach cancer . Cancer need not always begin as a tumour ; sometimes leukaemia and Hodgkin’s disease are spoken of as cancers of the blood and lymph, even when no tumour is involved.

Carcinoma refers specifically to a malignant tumour of an organ’s epithelial tissue, that is, the sheet-like membranes enclosing or lining it. Sarcoma , by contrast, is a malignant neoplasm of the body tissues themselves, particularly of the muscles or bones. The distinction is important since surgery is more often successful in completely eradicating the localized carcinoma , at least in its early stages, than the sarcoma , which can more readily begin spreading to other parts of the body.