The term neoplasia refers to a mass that has developed due to abnormal cell or tissue growth. Neoplasia refers to various types of growths including non-cancerous or benign tumors, precancerous growths, carcinoma in situ and malignant or cancerous tumors.

The term neoplasm is derived from a combination of the Greek words "neo" meaning new and "plasma" meaning formation.

One widely used definition of neoplasm is that described by the British oncologist R.A. Willis which stated: "A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues, and persists in the same excessive manner after cessation of the stimulus which evoked the change.".

However, this definition is challenged and criticized somewhat owing to the fact that some benign growths such as skin moles do not progress, as this definition suggests.

Although neoplasms often comprise more than one cell type, their initial development and growth is dependent on a population of one single type of neoplastic cells descended form one progenitor. These identical cells from a shared ancestry are referred to as clonal cells.

In some cases, genetic features shared between all the neoplastic cells can be demonstrated to prove the cells' clonality. However, this is not always possible and clonality is therefore not considered compulsory to define neoplasia.

The term oncology is derived from the Greek word "onkos" meaning bulk or mass and "logy" which means the study of. The term tumour used to be applied in cases of swelling caused by inflammation. Now, the term is used exclusively within the context of neoplasia.

Tumor components

The tumor comprises two basic components:

1. The proliferating neoplastic cells that make up the main tumour
2. The supportive stroma that is made up of the blood vessels and the connective tissues