Tumour

Tumour, a swelling or enlargement, due to the development of new growth in the part of the body affected. It is not usual to include under the term tumour cases of simple hypertrophy of organs, and swellings which result from inflammation or from the diseases known as the infective granulomata (tubercle, lupus, syphilis,leprosy, glanders, and actinomycosis). When the swelling consists of tissue similar to that normally present in the part affected the tumour is said to be homologous, while it is on the other hand termed heterologous when it is made up of embryonic tissue, and is therefore dissimilar to the tissues of its place of development. Tumours are divided into two classes, innocent and malignant. The former are usually homologous, they are often encapsuled, and in their growth they remain readily separable from surrounding structures, into which they do not extend, but which they rather thrust aside. The new formation is thus, as a rule, easily dealt with by operative treatment, it being a simple matter to dissect out the tumour, and when this is completely effected there is no likelihood of recurrence. The growth of an innocent tumour is slow, and it does not cause similar growth in the neighbouring lymphatic glands, or in remote parts of the body. A malignant tumour, on the other hand, increases rapidly in size, and infiltrates the surrounding tissues - that is to say, it extends into them so that it is difficult to say where the new growth ends and where sound tissue begins. Again, it often sets up similar growth in the nearest group of lymphatic glands, and it may be in distant parts of the body. It is hence no easy matter in many cases of malignant disease to remove the morbid tissue, and if this is not effected the tumour usually recurs. Hence the great importance of dealing with malignant growths in their early stages, before the disease has become widely infiltrated, and before any secondary deposits of the growth have occurred. Innocent tumours may be composed of various kinds of fully-developed tissue, e.g. fatty, fibrous, cartilaginous, osseous, muscular, nervous, and vascular tissues. Malignant tumours consist for the most _part of carcinomatous and sarcomatous tumours; the former (the true cancers) are of epithelial origin [CANCER]; the latter are composed of embryonic elements of a connective tissue type, and consist of cells and of a surrounding matrix. According to the shape of the cells which are present the sarcomata are divided into the round-celled, spindle-celled, mixed-celled, and giant-celled varieties. Cysts (q.v.) are sometimes included under the designation tumour.