Cancer is the disease that is characterized by any malignant tumor or growth resulting from the abnormal or uncontrolled division of cells. Cancer cells start showing defects in control mechanisms that control their division, and feedback systems that are important in regulating control mechanisms. On the other hand, normal cells grow under control mechanisms such as growth factors. If they are damaged, they are either repaired or they go through the process of cell death. In contrast to cancer cells, normal cells divide only a limited number of times.
All the mechanisms of normal cells are controlled by different kinds of proteins, and the damage to these proteins result in the problem of cancer. Damage to proteins is usually caused by mutations that cause damage to the DNA sequence of their genes.
Distinguishing features of cancer cells
Cancer cells are different from normal cells. There are 6 characteristics of cancer cells (“Hallmarks of cancer”) that make them different from other normal cells (Hanahan, 2011). These are as follows:
- Cancer cells have sustained proliferative signaling resulting in the stimulation of cells’ own growth.
- They show a clear escape from growth suppressors or growth-inhibiting signals.
- They resist cell death or apoptosis.
- They have a better copying ability from the parent cells (replication) that is helpful in expanding their numbers.
- They affect other cells to make new blood vessels (angiogenesis) for a blood supply.
- They are actively involved in the spread of the disease i.e. metastasis.
Cancer cells also show abnormal metabolic pathways as reported by Weinberg and Hanahan in 2011.
1. Self-sufficiency of cancer cells in growth
Cancer cells are self-sufficient in their growth, i.e. they don’t need growth signals or growth factors from outer sources. In fact, some cancer cells have the ability to develop their own growth signals as, for example, sarcomas – cancer arising from connective tissues – develop their own tumor growth factor-α (TGF-α), and glioblastomas – a kind of brain tumor – can develop their own platelet-derived growth factor (PDGF) (Rak, 2003).
2. Escape from growth suppressors
Cancer cells can easily escape from growth suppressors (anti-growth signals) from the surrounding environment.
3. Resisting cell death or apoptosis
Apoptosis refers to the programmed death of cells, or cell suicide. Cancer cells are able to resist this phenomenon.
The process of apoptosis consists of the working of sensors and effectors. Sensors are composed of survival signals as well as their receptors. They are able to check the abnormal behavior of cells such as DNA damage, low oxygen, or oncogene overexpression. Sensors consist of IGF-1/IGF2 and their accompanying receptor IGF-1R; and IL-3 and its accompanying receptor, among other proteins. On the other hand, effectors are involved in the apoptosis. Effectors consist of FAS ligand and its accompanying receptor, and TNF-α and it’s accompanying receptor, among other proteins.
Moreover, p53 protein also starts the process of apoptosis in response to DNA damage. p53 is one of the most important proteins in cancer control. p53 is found to be mutated in more than 50% of cancers (Carbone et al., 2010).
4. Better copying ability of cancer cells
Cancer cells show better replicative ability as compared to normal cells. They can show indefinite level of growth and division, but those cells have deteriorated chromosomes that is why these cells are cancerous.
5. Formation of new blood vessels (angiogenesis) for a blood supply
Although cancer cells lack the ability of angiogenesis in the start, but with the passage of time cancer cells get remarkable ability of angiogenesis that is balanced by inducers such as vascular endothelial growth factor (VEGF), and acetic and basic fibroblast growth factor (FGF 1/2), and inhibitors such as thrombospondin-1, which is regulated by p53.
The process of angiogenesis is most commonly seen in the development of breast, cervix, and melanoma tumors.
6. Spread of the disease to other tissues
Cancer cells can easily move away from their site of origin and move to the other body parts.
Immunity and Cancer cells
Research has shown that immune system has the ability to control or remove cancer cells. So, the chances of cancer in people, who are using immunosuppressive drugs, is more than the general population. In these people, latent Epstein-Barr virus can be reactivated resulting in malignancy (Parham, 2014). However, three immunity-related features of cancer cells, which are distinguishing them from normal cells, are mentioned in another paper (Cavallo, 2011):
- Cancer cells have the ability to grow well in (long lasting) inflamed environment.
- They have the ability to escape from recognition as a result of protective system of the body
- They can put an end to reaction of immunity
These features are thought to be essential to convert a normal cell into a cancerous cell and important in the study of cancer. These features may change from mild to severe and from one area of the body to another.
…These cells are really malignant.
Carbone, D. P., Pass, H. I., Johnson, D. H., Cancer, I. A. S. L., & Minna, J. D. (2010). Principles and Practice of Lung Cancer: The Official Reference Text of the IASLC: Wolters Kluwer Health/Lippincott Williams & Wilkins.
Cavallo, F. et. al. (2011). 2011: the immune hallmarks of cancer. Cancer Immunology, Immunotherapy, 60(3), 319-326.
Hanahan, D. et. al. (2011). Hallmarks of Cancer: The Next Generation. Cell 144, 646-674.
Parham, P. (2014). The Immune System, Fourth Edition.
Rak, J. (2003). Oncogene-Directed Therapies: Humana Press.