NEOPLASIA (NOMENCLATURE AND CLASSIFICATION)

NOMENCLATURE AND CLASSIFICATION

INTRODUCTION. The term ‘neoplasia’ means new growth;the new growth produced is called ‘neoplasm’ or ‘tumour’.However, all ‘new growths’ are not neoplasms since examples of new growth of tissues and cells also exist in the

processes of embryogenesis, regeneration and repair,hyperplasia and hormonal stimulation. The proliferation and maturation of cells in normal adults is controlled as a result

of which some cells proliferate throughout life (labile cells),some have limited proliferation (stable cells), while others do not replicate (permanent cells). On the other hand,

neoplastic cells lose control and regulation of replication and form an abnormal mass of tissue.

   Therefore, satisfactory definition of a neoplasm or tumour is ‘a mass of tissue formed as a result of abnormal, excessive,

uncoordinated, autonomous and purposeless proliferation of cells even after cessation of stimulus for growth which caused it’. The

branch of science dealing with the study of neoplasms or tumours is called oncology (oncos=tumour, logos=study).Neoplasms may be ‘benign’ when they are slow-growing and

localised without causing much difficulty to the host, or ‘malignant’ when they proliferate rapidly, spread throughout the body and may eventually cause death of the host. The

common term used for all malignant tumours is cancer.Hippocrates (460-377 BC) coined the term karkinos for cancer of the breast. The word ‘cancer’ means crab, thus reflecting

the true character of cancer since ‘it sticks to the part stubbornly like a crab’.

   All tumours, benign as well as malignant, have 2 basic components:

•‘Parenchyma’ comprised by proliferating tumour cells;parenchyma determines the nature and evolution of the

tumour.

•‘Supportive stroma’ composed of fibrous connective tissue and blood vessels; it provides the framework on which the parenchymal tumour cells grow.

    The tumours derive their nomenclature on the basis of the parenchymal component comprising them. The suffix ‘-oma’ is added to denote benign tumours. Malignant tumours

of epithelial origin are called carcinomas, while malignant mesenchymal tumours are named sarcomas (sarcos = fleshy)However, some cancers are composed of highly

undifferentiated cells and are referred to as undifferentiated malignant tumours.

    Although, this broad generalisation regarding nomenclature of tumours usually holds true in majority of instances, some examples contrary to this concept are:

melanoma for carcinoma of the melanocytes, hepatoma for carcinoma of the hepatocytes, lymphoma for malignant tumour of the lymphoid tissue, and seminoma for malignant

tumour of the testis. Leukaemia is the term used for cancer of blood forming cells.

SPECIAL CATEGORIES OF TUMOURS. Following categories of tumours are examples which defy the generalisation in nomenclature given above:

1. Mixed tumours. When two types of tumours are combined in the same tumour, it is called a mixed tumour.

For example:

i) Adenosquamous carcinoma is the combination of adenocarcinoma and squamous cell carcinoma in the endometrium.

ii) Adenoacanthoma is the mixture of adenocarcinoma and benign squamous elements in the endometrium. 

iii) Carcinosarcoma is the rare combination of malignant tumour of the epithelium (carcinoma) and of mesenchymal tissue (sarcoma) such as in thyroid. 

iv) Collision tumour is the term used for morphologically two different cancers in the same organ which do not mix with each other. 

v) Mixed tumour of the salivary gland (or pleomorphic adenoma) is the term used for benign tumour having combination of both epithelial and mesenchymal tissue 

elements.

2. Teratomas. These tumours are made up of a mixture of various tissue types arising from totipotent cells derived from 

the three germ cell layers—ectoderm, mesoderm and endoderm. Most common sites for teratomas are ovaries and testis (gonadal teratomas). But they occur at extra-gonadal sites as well, mainly in the midline of the body such as in the head and neck region, mediastinum, retroperitoneum,sacrococcygeal region etc. Teratomas may be benign or mature (most of the ovarian teratomas) or malignant or immature (most of the testicular teratomas). 

3. Blastomas (Embryomas). Blastomas or embryomas are a group of malignant tumours which arise from embryonal or partially differentiated cells which would normally form blastema of the organs and tissue during embryogenesis.These tumours occur more frequently in infants and children 

(under 5 years of age) and include some examples of tumours in this age group: neuroblastoma,nephroblastoma (Wilms’ 

tumour), hepatoblastoma, retinoblastoma, medulloblastoma, pulmonary blastoma. 

4. Hamartoma. Hamartoma is benign tumour which is made of mature but disorganised cells of tissues indigenous to the particular organ e.g. hamartoma of the lung consists of 

mature cartilage, mature smooth muscle and epithelium. Thus, all mature differentiated tissue elements which comprise the bronchus are present in it but are jumbled up as a mass. 

5. Choristoma. Choristoma is the name given to the ectopic islands of normal tissue. Thus, choristoma is heterotopia but is not a true tumour, though it sounds like one. 

CLASSIFICATION. Currently, classification of tumours is based on the histogenesis (i.e. cell of origin) and on the anticipated behaviour (Table). However, it must be mentioned here that the classification described here is only

a summary. Detailed classifications of benign and malignant tumours pertaining to different tissues and body systems along with morphologic features of specific tumours appear in the specific chapters of Systemic Pathology later.