Graphical Guide To Cancer Biology

This page presents a collection of graphics to explain key differences between normal and cancer cells. Most of the ideas shown below are explained in more detail on other pages. On this page we use only a few words and let the graphics provide the explanations.

Every case of cancer, in every patient, is unique. No two breast cancers or prostate cancers are identical. This variation is one of the things that makes cancer hard to treat. 

Even with all the differences, all cancers DO share a set of common features. In 2000, Robert Weinberg and Douglas Hanahan published a paper that lists and described some of the most important things that cancers have in common - the 'Hallmarks of Cancer'.1 The cartoons below are based on this work and observations that have some since.

Note that additional details on ideas illustrated below can be found in: What is cancer? 
In-depth descriptions of these and other topics are presented in the Cancer Biology section of the site.

How are cancer cells different from normal cells?  


Normal cells only reproduce when they are given 'orders' to do so. They stop when those signals are removed.

When the man is not stepping on the button, the signal stops and normal cells stop dividing.

cancer cells reproduce by supplying their own signals - cartoon

Cancer cells are able to reproduce without normal signals. They are stuck in the 'on' position.

normal cells stop reproducing and don't pile up on each other when given 'stop' signals

Normal cells will stop reproducing when they are told to do so. This prevents cells from crowding each other or piling up. 

cancer cells reproduce uncontrollably and pile up on each other

Cancer cells ignore 'stop' signals and continue to reproduce. This leads to crowding and cells piling up on each other.

Normal cells have a built in lifespan. They can only reproduce a set number of times.

Normal cells have a built-in number of times that they are able to reproduce

Cancer cells can divide an unlimited number of times. They are immortal.

Cancer cells are able to reproduce an unlimited number of times.

Normal cells kill themselves via the process called apoptosis when they are damaged.

Normal cells will commit cellular suicide (apoptosis) when they become damaged.

Cancer cells are able to avoid cellular suicide (apoptosis).

Cancer cells can defend themselves and survive even when they're damaged.

All cells require the nutrition and oxygen provided by the blood supply. Normal blood vessels are organized and efficient.

Blood vessels provide nutrients and oxygen to cells. They are frequently built and repaired. The process is very organized and efficient. Examples include wound healing and the menstrual cycle.

Cancer blood vessels are disorganized and leaky. The process (angiogenesis) is still essential to tumor growth.

Tumors need blood vessels to survive, but the blood vessels are abnormal, twisted and leaky. This can lead to treatment resistance and the spread of cancer.

Cancer cells spread to distant parts of the body by following 'leaders'. They cut their way past nearby defenses and migrate away.

Normal cells (other than those in the blood) stay in place. Cancer spread (metastasis) involves the movement of cancer cells from a tumor to distant places in the body.

The spread of cancer often occurs when cancer cells enter nearby blood vessels and float away.

Cancer cells can use the defective blood vessels found in tumors to travel to places in the body far from the original location.

Normal cells can repair DNA damage (mutation) and are all the same.

When the genes (DNA) of normal cells gets damaged, it is repaired. The result is that all of the cells are genetically the same.

Cancer cells can not repair DNA damage (mutation) well and accumulate new changes over time. They are not the same as each other - even in the same person.

Cancer cells do not repair their DNA well. They gain changes over time. The cancer cells in a tumor are similar, but not exactly the same.


  • 1. Hanahan, D., & Weinberg, R. (2000). The hallmarks of cancer. Cell, 100(1), 57-70. [PUBMED]