Hallmarks of Cancer

Evading Growth Suppressors

The second Hallmark of Cancer is the cell’s ability to evade growth suppressors. In other words, the cell is able to avoid factors that would normally control and contain cell growth and instead continue to proliferate. Normal, healthy cells often control proliferation with these growth suppressor. With research of this Hallmark of Cancer, several suppressive genes that inhibit cellular growth and proliferation have been discovered. They are TP53, PTEN, and RB.

When a stimulus, either internal or external, activates these suppressive genes, they can cause the cell cycle to halt, induce senescence, or apoptosis of the cell. Senescence is when the cell is no longer able to divide and grow. Apoptosis is an automated death response of the cell. This occurs in healthy cells as a way to control cellular growth and development.

With cancer cells, these suppressive genes are repressed. If the gene is not expressed, the gene cannot be activated and growth cannot be controlled. Cancer cells can completely lose the suppressive gene or create mutations of the gene so that it cannot be expressed and activated. A mutation or deletion of the TP53 gene is a prevalent cause for human tumors.

An example of this Hallmark of Cancer can be seen with the human papilloma virus (HPV) and its relation to cervical cancer. Oncoproteins E6 and E7 of HPV are able to interfere and inactivate the suppressive genes TP53 and RB of cells and contribute to the formation of the tumor. The human papilloma virus (HPV) is the most common sexually transmitted virus in the United States. HPV may contribute to cervical cancer in women, which is the 2nd leading cause of death of women worldwide. Although there is no cure, vaccination prior to infection from the virus can prevent development of cervical cancer, as well as other types of cancer.¹

¹ Human Papillomavirus (HPV) Vaccine (Gardasil). MedlinePlus. https://medlineplus.gov/druginfo/meds/a607016.html. February 15, 2017.