There are many differences between cancer cells and normal cells. Some of the differences are well known, whereas others have only been recently discovered and are less well understood. You may be interested in how cancer cells are different as you are coping with your own cancer or that of a loved one. For researchers, understanding how cancer cells function differently from normal cells lays the foundation for developing treatments designed to rid the body of cancer cells without damaging normal cells.
The first portion of this list discusses the basic differences between cancer cells and healthy cells. For those who are interested in some of the more difficult-to-understand differences, the second portion of this list is more technical.
If you wish to review what a cell is before discussing cancer cells, our About.com Guide to Biology provides this excellent description of the cell:
And, for a definition and description of cancer cells:
A brief explanation of the proteins in the body that regulate cell growth is also helpful in understanding cancer cells. Our DNA carries genes that in turn are the blueprint for proteins produced in the body. Some of these proteins are growth factors, chemicals that tell cells to divide and grow. Other proteins work to suppress growth. Mutations in particular genes (for example those caused by tobacco smoke, radiation, ultraviolet radiation, and other carcinogens) can result in the abnormal production of proteins. Too many may be produced, or not enough, or it could be that the proteins are abnormal and function differently. Cancer is a complex disease, and it is usually a combination of these abnormalities that lead to a cancerous cell, rather than a single mutation or protein abnormality.
Cancer Cells vs Normal Cells
- Growth – Normal cells stop growing (reproducing) when enough cells are present. For example, if cells are being produced to repair a cut in the skin, when the repair work is done, cells are no longer reproduced to fill in the hole. In contrast, cancer cells don’t stop growing when there are enough cells present. This continued growth often results in a tumor (a cluster of cancer cells) being formed. Each gene in the body carries a blueprint that codes for a different protein. Some of these proteins are growth factors, chemicals that tell cells to grow and divide. If the gene that codes for one of these proteins is stuck in the “on” position by a mutation (an oncogene) – the growth factor proteins continue to be produced. In response, the cells continue to grow.
- Communication – Cancer cells don’t interact with other cells as normal cells do. Normal cells respond to signals sent from other nearby cells that say, essentially, “you’ve reached your boundary.” When normal cells “hear” these signals they stop growing. Cancer cells do not respond to these signals.
- Cell repair and cell death – Normal cells are either repaired or die (undergo apoptosis) when they are damaged or get old. Cancer cells are either not repaired or do not undergo apoptosis. For example, one protein called p53 has the job of checking to see if a cell is too damaged to repair, and if so advise the cell to kill itself. If this protein p53 is abnormal or inactive (for example, from a mutation in the p53 gene,) then old or damaged cells are allowed to reproduce. The p53 gene is one type of tumor suppressor gene that code for proteins that suppress the growth of cells.
- Stickiness – Normal cells secrete substances that make them stick together in a group. Cancer cells fail to make these substances, and can “float away” to locations nearby, or through the bloodstream or system of lymph channels to distant regions in the body.
- Ability to Metastasize (Spread) – Normal cells stay in the area of the body where they belong. For example, lung cells remain in the lungs. Cancer cells, because they lack the adhesion molecules that cause stickiness, are able to travel via the bloodstream and lymphatic system to other regions of the body. Once they arrive in a new region (such as lymph nodes, the lungs, the liver, or the bones) they begin to grow, often forming tumors far removed from the original tumor.
- Appearance – Under a microscope, normal cells and cancer cells may look quite different. In contrast to normal cells, cancer cells often exhibit much more variability in cell size – some are larger than normal and some are smaller than normal. In addition, cancer cells often have an abnormal shape, both of the cell, and of the nucleus (the “brain” of the cell.) The nucleus appears both larger and darker than normal cells. The reason for the darkness is that the nucleus of cancer cells contains excess DNA. Up close, cancer cells often have an abnormal number of chromosomes that are arranged is a disorganized fashion.
- Rate of growth – Normal cells reproduce themselves and then stop when enough cells are present. Cancer cells reproduce rapidly before the cells have had a chance to mature.
- Maturation – Normal cells mature. Cancer cells, because they grow rapidly and divide before cells are fully mature, remain immature. Doctors use the term undifferentiated to describe immature cells (in contrast to differentiated to describe more mature cells.) Another way to explain this is to view cancer cells as cells that don’t “grow up” and specialize into adult cells. The degree of maturation of cells corresponds to the "grade" of a cancer. Cancers are graded on a scale from 1 to 3 with 3 being the most aggressive.
- Evading the immune system – When normal cells become damaged, the immune system (via cells called lymphocytes) identifies and removes them. Cancer cells are able to evade (trick) the immune system long enough to grow into a tumor by either by escaping detection or by secreting chemicals that inactivate immune cells that come to the scene.
- Functioning – Normal cells perform the function they are meant to perform, whereas cancer cells may not be functional. For example, normal white blood cells help fight off infections. In leukemia, the number of white blood cells may be very high, but since the cancerous white blood cells are not functioning as they should, people can be more at risk for infection even with an elevated white blood cell count. The same can be true of substances produced. For example, normal thyroid cells produce thyroid hormone. Cancerous thyroid cells (thyroid cancer) may not produce thyroid hormone. In this case the body may lack enough thyroid hormone (hypothyroidism) despite an increased amount of thyroid tissue.
- Blood supply – Angiogenesis is the process by which cells attract blood vessels to grow and feed the tissue. Normal cells undergo a process called angiogenesis only as part of normal growth and development and when new tissue is needed to repair damaged tissue. Cancer cells undergo angiogenesis even when growth is not necessary. One type of cancer treatment involves the use of angiogenesis inhibitors – medications that block angiogenesis in the body in an effort to keep tumors from growing.
More Differences Between Cancer Cells and Normal CellsThis list contains further differences between healthy cells and cancer cells. For those who wish to skip these technical points, please skip to the next subheading – summarizing the differences.
Summarizing the DifferencesAs noted above, there are many differences between normal cells and cancer cells. Also noteworthy is the number of “checkpoints” that need to be bypassed for a cell to become cancerous. The cell needs to have growth factors that prompt it to grow even when growth is not necessary. It has to evade proteins that direct cells to stop growing and die when they become abnormal. They need to evade signals from other cells, and they need to lose the normal “stickiness” (adhesion molecules) that normal cells produce. All in all it is very difficult for a normal cell to become cancerous, which may seem surprising considering that 1 in 2 men and 1 in 3 women will develop cancer in their lifetime. The explanation is that in the normal body, roughly 3 billion cells divide every single day. “Accidents” in reproduction of the cells caused by heredity or carcinogens in the environment during any of those divisions can create a cell that, following further mutations, can develop into a cancer cell.
American Cancer Society. Testing Biopsy and Cytology Specimens for Cancer. What do doctors look for under the microscope? Updated 03/24/10. http://www.cancer.org/treatment/understandingyourdiagnosis/examsandtestdescriptions/testingbiopsyandcytologyspecimensforcancer/testing-biopsy-and-cytology-specimens-for-cancer-what-doctors-look-for
DeBaradinis, R. et al. The biology of cancer: metabolic reprogramming fuels cell growth and proliferation. Cell Metabolism. 2008. 7(1):11-20.
National Cancer Institute. SEER Training Module. Cell Biology of Cancer. Accessed 01/17/13. http://training.seer.cancer.gov/disease/cancer/biology/
National Cancer Institute. What is Cancer? Updated 02/06/12. http://www.cancer.gov/cancertopics/cancerlibrary/what-is-cancer