As shown in Figure 4 below, the transformation from a normal cell to a cancer cell takes several progressive stages. Normal cells have well-defined borders and are of regular shape or morphology. At the very first stage of abnormal growth, the regular shape is maintained but there is excess cell growth. Over time, cells also become irregular in shape, followed by tumor formation within a confined area (this is referred to as in situ) until tumor cells become mobile and invasive to neighboring healthy cells, tissues, and organs.
The general stages in which normal cells become cancer cells are as follows:
Normal --> Hyperplasia --> Dysplasia --> Carcinoma in situ --> Malignancy
Hyperplasia is defined as overgrowth or an increase in the number of cells in tissues or organs.
Dysplasia is defined as cells with an abnormal appearance but are not cancerous.
Carcinoma in situ is defined as a cluster of abnormal cells in a confined area where it is initially formed.
Malignancy is defined as cancer undergoing uncontrolled cell growth and invasion to nearby tissues or organs.
