Briefly describe the mechanism whereby normal cells are transformed into cancer cells.

The transformation of normal cells into cancer cells, also known as carcinogenesis, is a complex process that occurs in several stages. Here's a step-by-step description:

1. Initiation: This is the first step where a normal cell undergoes a genetic mutation. This mutation can be caused by various factors such as exposure to carcinogens (like tobacco smoke, radiation, certain chemicals, etc.), viruses, or inherited genes. This mutation affects the genes that control cell growth and division, causing the cell to become a "cancer-initiated" cell.

2. Promotion: In this stage, the initiated cell is stimulated to divide more rapidly. This can be due to various factors such as chronic inflammation, hormonal imbalances, or immune system suppression. The rapid division of cells increases the chance of additional mutations and the development of a tumor.

3. Progression: This is the final stage where the tumor becomes malignant. The cancer cells become more aggressive and gain the ability to invade surrounding tissues and spread to other parts of the body (metastasis).

It's important to note that not all initiated cells become cancerous, as the body has mechanisms to repair DNA damage or destroy potentially cancerous cells. However, if these mechanisms fail, the initiated cell can continue to divide and potentially develop into cancer.