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According to a publication written by Douglas Hanahan from the Swiss Institute for Experimental Cancer Research and the UCSF Department of Biochemistry and Biophysics and Robert A. Weinberg from the Whitehead Institute for Biomedical Research, there are six biological capabilities acquired during the development of human tumors that are defined as the hallmarks of cancer. The six hallmarks include sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis. That may all sounds complex and confusing but over the course of this post, I will explain each of the hallmarks individually in a simple to understand fashion.


One of the most fundamental traits of cancer is the ability for cancer cells to grow and duplicate constantly. When cells grow and duplicate, it is referred to as proliferation. Normal tissue cells control and regulate the production of signals that promote proliferation in cells, therefore maintaining a balance of cell number and function. Cancer cells, on the other hand, do not regulate these proliferation signals and they sustain proliferative signaling causing cancers to grow uncontrollably.

In addition to normal tissue regulating the signals that promote proliferation, normal tissue also use growth suppressors to inhibit cell growth. Cancer cells have been able to evade these growth suppressors, also allowing them to grow uncontrollably. In human cells, there are dozens of growth suppressors that operate in a number of ways to limit cell proliferation. It has been discovered that in animal and human cancers, these growth suppressors are nearly always inactivated.

In addition to growing uncontrollably, cancers also resist cell death or apoptosis. In normal cells, “contact inhibition”, a mechanism that promotes cell death when the population of normal cells becomes too dense, regulates cell numbers. Cancer cells lose this “contact inhibition” and can grow indefinitely to form tumors. Also, apoptosis or cell death serves as a natural barrier to cancer development in normal cells. Cancer cells avoid apoptosis; as a result, tumors are able to grow indefinitely.

Normal cells can only replicate a limited number of times before being unable to replicate anymore. Cancer cells require unlimited replicative potential in order to generate macroscopic (visible to the human eye) tumors. As a result, cancer cells come up with a number of mechanisms for enabling replicative immortality.

Like normal tissue, cancerous tissue requires nutrients and oxygen as well as a way to get rid of wastes and carbon dioxide. Tumors address these needs through the induction of angiogenesis. Angiogenesis is the creation of blood vessels. Blood vessels to and through the cancerous tumors allow the tumors to receive the nutrients and oxygen they need and eliminate wastes and carbon dioxide.

Lastly, cancers activate invasion and metastasis. Cancers begin in a localized area. After growing to a respectable size, cancers will attempt to spread to other parts of the body by using the circulatory system and lymphatic system. Once the cancer spreads to other parts of the body, the cancer will attempt to grow in its new locations.

The original publication can be found at Please be aware that this is a very scientific and difficult read.

Cancer is a broad group of diseases, all of which involve unregulated cell growth. There are over 200 different known cancers that affect humans.  The type of cell that is initially affected classifies each cancer. Cancer harms the body when affected or damaged cells divide uncontrollably to form tumors or masses of tissue. Benign tumors generally demonstrate limited growth and stay in a single spot. On the other hand, malignant tumors spread to other parts of the body using the blood and lymph systems. Malignant tumors are more dangerous than benign tumors.

A short video explaining what cancer is:

Normal healthy cells go through a cell cycle of growth, division, and death.  Normally, different genes in the cell cycle tell the cell when to divide and when not to divide, fix any errors in the replication of the cells, and if anything goes wrong, to kill the cells through a process called apoptosis. In cancer cells, these genes are damaged or mutated and therefore do not perform their roles in cell division, resulting in uncontrollable cell growth.


A number of factors can increase ones chances of getting cancer. Genes inherited from family members can increase ones chance of getting cancer. It is possible to be born with genetic mutations or faulty genes that statistically increases one’s chances of getting cancer later in life.  Exposure to carcinogens, a class of substances that is directly responsible for damaging DNA, also increase ones chances of getting cancer. Examples of carcinogens are tobacco, arsenic, radiation, and asbestos. Lastly, several viruses have been linked to cancer such as HPV (which is linked to cervical cancer), hepatitis B and C (which is linked to liver cancer), and HIV.

Cancer symptoms are varied and depend greatly on many factors such as where the cancer is located, where it has spread, and how big the tumor is. Certain cancers can be seen through the skin. For example, a lump on the breast can be an indicator of breast cancer or a bump on the testicle can be an indicator of testicular cancer. Changes in a wart or mole on the skin are an indicator of skin cancer. Other cancers have symptoms that are not as visible. Colon, bladder, and prostate cancers do not have any visible indicators but can be indicated by other symptoms. Colon cancer often results in constipation and diarrhea. Bladder and prostate cancers cause changes in bladder function. Pain may not be felt until the tumor has grown and begins to push against nearby nerves.

There is no single treatment for cancer and patients often receive several treatments crafted specifically for them. Cancer treatment depends on the type of cancer, how much the cancer has spread, and other factors such as age and health. Cancer treatments can be grouped into surgery, radiation, or chemotherapy. If the cancer has not spread, surgery can be used to completely remove the cancer from the body, effectively curing the patient. Radiation involves focusing high-energy beams onto the cancer cells, forcing them to commit suicide. Normally, these high-energy beams would damage normal, healthy tissue but medical advances have made it so that the beams can be accurately targeted. Chemotherapy uses chemicals that target rapidly dividing cells in the body (not just cancer cells). However, normal cells can usually recover from the damage induced by chemotherapy while cancer cells cannot. Chemotherapy treatment is performed in cycles so that the body has time to heal between doses.

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