Final answer:
Normal cells can be transformed into cancer cells through exposure to carcinogens, infections by viruses that insert or activate oncogenes or disrupt tumor suppressor genes, and a family history of cancer due to inherited mutations.
Step-by-step explanation:
The transformation of normal cells into cancer cells can occur due to several mechanisms:
- Exposure to carcinogens - These are substances that can cause changes or mutations in the DNA of cells. Examples include tobacco smoke, radiation, and certain chemicals.
- Infections by viruses - Certain viruses carry genes that, when inserted into a cell's genome, can lead to cancer. These genes may be oncogenes that are overactive, or they may disrupt the normal function of proto-oncogenes and tumor suppressor genes.
- A family history of cancer - Inherited genetic mutations can greatly increase the likelihood of certain types of cancer, due to mutations being passed down through generations, affecting the same genes that could become oncogenes or ineffective tumor suppressor genes.
The three factors listed play a significant role in converting normal cells into cancerous ones. This process is part of a multi-step event that involves the initiation, promotion, progression, and finally malignancy of cells. Ultimately, it is the accumulation of multiple genetic changes that lead a normal cell to become cancerous.