Cancer, Part 1 – How cancer cells differ

Cancer is a disease wherein cells in the body grow uncontrollably and can spread locally or to other tissues and organs. These two properties – sustained replication and spread to other body parts – are what define cancer cells. 

Normal cells grow and replicate until new cells are no longer needed. For example, when you have a cut in your skin, undamaged skin cells replicate to heal the wound. They do so in response to signals sent by nearby cells. When the healing process is complete the damaged cells die and the normal skin cells stop replicating. If they didn’t, a clump of skin cells would form, i.e. a tumor. The tumor might be benign, meaning that cells making up the tumor would eventually stop replicating, and they would not spread to other parts of the body. Benign tumors are made of cells that are normal or nearly normal in appearance under the microscope. When they are surgically removed in full they do not usually grow back. 

How are cancer cells different from normal, healthy cells?

• Cancerous, or malignant, cells look different than normal cells. They range from looking very primitive and bizarre to looking almost like normal cells. Their chromosomes may have missing pieces called deletions. Some have extra chromosomal fragments or even extra intact chromosomes called replications.

• Cancer cells continue to replicate indefinitely. They do not need or even respond to signals from nearby cells that would tell normal cells to stop replicating.

• Eventually some of these abnormal, cancerous cells might break off from the tumor and spread through the bloodstream or lymphatic channels to distant tissues. There, they invade the normal tissue, where they resume the process of replication and spreading further. This spread to other areas in the body is called metastasis.

• Cancer cells hide from the immune system, which would normally recognize them as foreign and destroy them. Cancer cells may even trick the immune system into protecting them. 

• Cancer cells may use different nutrients than normal cells – their metabolism may be distinct. This may facilitate rapid growth. 

The differences between normal and cancer cells may provide opportunities for treatment discovery. For example, if a particular cancer cell type needs alternative energy sources compared to normal cells, removing these nutrients may cause the cancer cells to die. Because cancer cells may grow rapidly, they may be more sensitive to chemotherapy that poisons the replication process. Because they may have unique markers on their cell surfaces, they may be targeted by immunotherapy approaches. More on chemo- versus immunotherapy later.

Note: Although I am a physician, the content in this article is not meant to diagnose, treat, cure or prevent illness or disease in the reader – it is for educational purposes only.

References

• Jenks S. Downgrading cancer definitions: overdiagnosis fuels the discussion. J Natl Cancer Inst. 2014 Mar;106(3):dju070.
• Encyclopedia of Cancer, 3^rd ed. Schwab M, editor. Heidelberg ; New York : Springer, 2018- (continuously updated edition).
• What is Cancer? National Cancer Institute, https://www.cancer.gov/about-cancer/understanding/what-is-cancer