By Dr Ananya Mandal, MD
The body is composed of trillions of cells. These normal cells grow, mature, function and divide into new cells and eventually die off in a tightly regulated system. During the early years of a person’s life the normal cells divide faster to allow the person to grow. Once adulthood is reached the cells divide only when they need to replace worn-out or dying cells or to repair injuries.
The growth and death of cells is regulated by the DNA present in the nucleus of the cells. The DNA essentially provides a blueprint that guides the cell in each of its functions.
Cancer begins when cells in a part of the body grow without control. When the DNA is damaged, it can repair itself by several mechanisms. When repair fails, the cell normally kills itself in a process called apoptosis. Sometimes neither of these protective forces work and the rogue cell continues to grow and multiply without dying. It passes its faulty DNA to the newly formed cells as well. Cancer cells can also invade into other tissues, something that normal cells cannot do. A Damaged DNA may also be inherited from parents.
Sometimes the cause of the DNA damage is obvious like exposure to sun’s UV rays, or exposure to radiation, exposure to cigarette smoke etc. But often no clear cause is found.
Most basal cell and squamous cell skin cancers are caused by skin exposure to ultraviolet rays from sunlight and from artificial sources of such rays like tanning beds and sunlamps. Excess exposure to the sun for long periods of time, especially before the age of 30, is a high risk for developing skin cancers later in life. Frequent sunburns in childhood may increase the risk for basal cell cancer many years or even decades later.
Several genes have been noted to have associations with skin cancers. Genes that help cells grow and divide are called oncogenes. There are good genes called tumor suppressor genes that keep growth of the rogue cells in check and cause them to die at the right time. Cancers are caused when DNA changes turn on oncogenes or turn off tumor suppressor genes. Sometimes more than one DNA change is needed to cause cancer.
Common genes that underlie squamous cell cancers include TP53. This is a tumor suppressor gene that causes cells with damaged DNA to die. When TP53 is altered, these abnormal cells may live longer and become cancer cells.
A gene commonly affected in basal cell cancers includes the “patched” (PTCH) gene, which is part of the hedgehog signalling pathway. This pathway is vital in the development of the embryo and baby within the womb. PTCH is a tumor suppressor gene that turns into an oncogene.
People who have basal cell nevus syndrome - a condition inherited from either parent - may have an altered PTCH gene in all the cells of their body resulting in many basal cell cancers.
Apart from UV radiations from sunlight, viruses like Human Papilloma virus (HPV) also can causes changes in DNA leading to skin cancers.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)