What is Cancer?

This article provides a simple model to begin to understand a very basic model of cancer.  The heterogeneity of the term cancer is emphasized. The term cancer is associated with much emotion and misperception.  What most people hear the word cancer – they immediately think of someone who is terribly sick or dying.  When someone is told that a relative has cancer or even that they have cancer, often the first reaction is that this is a death sentence.  What is cancer and what does the term truly mean?  By beginning to understand what the word means some of the mystery and fear can be taken away.

The following analogy is not perfect but attempts to relate cancer biology and genetics to an easily understandable model.  Our body is composed of millions of cells that each function like little independent workers in a giant factoryThere are rules in this factory that govern the function and roles of each worker.  In general, most workers (or cells) can only perform one function and must stay in an area or line where there are similar workers performing the same tasks.  There are ropes or boundaries that these workers must stay within.  When a worker gets out of line or strays, they will be sent back to their work area or may even be fired.

Most workers in the factory are highly specialized and do only one specific job – such as a push a button or carry boxes between two spots all the time.  A few workers have the ability to supervise or do multiple roles.  When new workers are hired, the initially have the ability to do many roles but over time they find the job that best suits them and lose their ability to do many different types of jobs.  Rarely, a worker will decide he wants to abandon his place on the factory line and go to another part of the factory that is not his home.  He is going to disruptive their and causes a commotion.  If the supervisors spot the disruption he will be sent back or fired – usually fired and forced to leave the factory.  If several workers move and cause disruption, this will cause great disharmony in the factory and overwhelm the governing abilities.  The factor may even begin to lose production or be forced to shut down.   In addition to supervisors, the factory also has special teams of security guards that provide protection and surveillance.  If a security guard sees trouble, they sound the alarm brining many more guards to the area of trouble.

Although the above scenario may seem very simplistic, it provides a framework to discuss normal cell functioning and regulation.  Our body is the factory and is composed of many organ systems that each has unique cells that perform specific functions.  The unique cellular functions or roles are defined by each cells genetic program within its DNA.  The program for functioning of each cell is contained in its genes like a computer program.  Although all of our cells have DNA, certain parts of the DNA are turned on and tell each cell its specific role in the factory.  The “ropes” or boundaries that keep cells in their optimal work area are structures such as the basement membrane as well as contact inhibition that prevents normal cells from growing into adjacent structures.  Under the microscope, a hallmark of cancerous cells is that they tend to violate normal boundaries and grow past a basement membrane or into adjacent tissue.

The ability of a cell to do many jobs and then specialize is analogous to plouripotent stem cells that undergo terminal differentiation.  This primarily happens during early growth and development but can continue to a small extent later in life.  The ability of security guards (the immune system) to sound an alarm to take care of some troublesome cells is analogous to the exponential signaling system that our immune system uses.  When a surveillance t-cell recognizes an abnormal signal on a rouge cell, it has the ability to release chemical messengers that spread like wildfire and recruit more white blood cells to that area to help attack and control the “foreign” invader.  This system has the additional advantage of allowing a localized response in one area of the body only.

The major organ systems (or in the above analogy major divisions in the marvelous factory that is our body) are as follows:

  • Nervous System: Brain, spinal cord, nerves all function to transmit information and sensation
  • Respiratory System: Lungs and airways that allow breathing
  • Cardiovascular System: Heart and blood vessels that provide circulation
  • Gastrointestinal System:  Intestines and all the support organs that allow digestion of food and excretion of wastes
  • Musculoskeletal System: All the muscles and bones that allow movement, stability and protection
  • Renal System: The kidneys, ureters and bladder help regulate body water and wastes
  • Reproductive System: gonads and support structures that allow reproduction
  • Endocrine System: Glands within the body that send chemical messages to control many bodily functions such as the pituitary and adrenal glands
  • Lymphatic System: vessels that collect water and debris outside of cells
  • Integumentary system: Our covering, skin, provides protection and containment.
  • Hematologic System: Production of cells that transport nutrients and different kinds of protection.
  • Immune System: The security system of the “factory”

Each of these systems has different kinds of specialized cells that help that organ perform its function dictated by its genetic programming.  Cancer is a change in genes that causes abnormal cell function.  This may cause abnormal function of a particular system or may affect multiple other systems.   Almost all cancers share a common characteristic:  lack of respect for their normal cell boundaries.  The worker gets out of line and steps beyond their normal work environment.  For example, colon cancer is abnormal colon cells that violate the basement membrane and distort the healthy adjacent cells.  Colon cancer cells that grow outside of the colon and continue to make abnormal colon cells have no regulation and are termed metastatic.  Spread of cancer cells outside of their organ of origin is termed metastases.  Most bad effects of cancer are caused by either disruption of its home system function or by spread into other systems via metastases.

In the above analogy, the new workers with the ability to choose different roles are pluripotent stem cells.  The stem cells undergo terminal differentiation (or choose a role that they cannot give up).  The cells that leave their station or are disruptive at their station represent metastatic cells or locally invasive cancer cells, respectively.  The security guards are immune surveillance cells such as neutrophils, natural killer cells and T-cell lymphocytes.  They all have different ways to recognize abnormal cells and to call for backup.

If this sounds a bit vague or confusing that’s because it is!  Cancer is a very heterogeneous term and can describe thousands of types of disease.  To say that someone “has cancer” is very non-specific and as helpful as saying that someone “has some money.”  Do they have a penny or a million dollars?  Similarly to say that someone has cancer may imply they have a few abnormal cells that the body has cured itself of or on the other end of the spectrum they may have diffuse spread of a very aggressive cancer that will cause death.  This uncertainty and vagueness of the term cancer can cause much anxiety.  It is important to understand how the term is used and precisely what it is referring to before you draw conclusions about what is actually going on.  The hallmark of cancer is mutation of a cells genes causing abnormal cell function with growth of the cell outside of its normal boundaries.


  1. www.cancer.gov/cancertopics/cancerlibrary/what-is-cancer
  2. Abeloff, M.D. (2008). Abeloff: Abeloff’sClinical  Oncology, 4th ed. Chapter 10. Philadelphia, PA: Churchill Livingstone – Elsevier
  3. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.