Hallmarks of Cancer

All tumor cells begin as normal cells; however, these cells have found a way to acquire new biological abilities, now termed the hallmarks of cancer. There are 10 hallmarks of cancer:

1. Sustained proliferative signaling- Normal cells will only replicate when the appropriate signals are given, indicating sufficient space, nutrients, and new cells are needed. Cancer cells make more cells without the proper signal being given.
2. Evading growth suppressors- Normal cells will stop dividing when given signals that conditions are no longer favorable for division. Cancer cells ignore the signal to stop dividing.
3. Resisting cell death- Normal cells activate apoptosis or cell death when something is wrong with the cell or if errors cannot be repaired in the DNA during replication. Cancer cells ignore these signals; therefore, they do not die when they should.
4. Enabling replicative immortality- Normal cells stop dividing after a certain number of divisions determined by the length of their telomeres. Cancer cells do not stop dividing at that point; they may even extend their own 'clock' by activating an enzyme to lengthen their telomeres. This makes cancer cells immortal.
5. Inducing angiogenesis- Cells need oxygen to live. Cancer cells ensure their newly made cells survive by creating new blood vessels to feed oxygen and nutrients to the cancer cells.
6. Avoiding immune destruction- Cancer cells can learn to avoid immune cell destruction by upregulating proteins such as programmed death ligand 1 (PD-L1) that deactivate T-cells.
7. Activating invasion and metastasis- Normal cells respect the natural barriers of their environment. Cancer cells invade membranes and even break off of the tumor, travel throughout the body, and create new tumors.
8. Deregulating cellular energetics- Cancer cells divide rapidly and need more energy than normal cells. Normal cells use oxygen to make energy in a process called oxidative phosphorylation. Often, cancer cells are in anaerobic conditions and, therefore, need to be able to make energy without oxygen. Cancer cells circumvent this issue using anaerobic glycolysis to create energy or ATP.
9. Tumor-promoting inflammation- Immune cells are found within tumors. Initially, it was thought these immune cells were there to fight off cancer cells. Research has shown that cancer cells have intercepted these tumor-infiltrating immune cells and used them to help them promote tumor progression.
10. Genome instability and mutation- Normal cells stop during replication to inspect the newly made DNA and ensure it is error-free. Cancer cells bypass these checkpoints, introducing more errors per replication cycle. Cancer cells also go through more replication cycles than normal cells. If errors are introduced into DNA repair genes that render the protein useless, the cancer genome's error rate will increase rapidly. This leads to cancer cells having a highly unstable and mutated genome.