Part 1

The subject of our genes and cancer is one that is especially relevant to not only the millions of present day cancer sufferers, but also to their family members - past, present and future. To understand the significance of these words, it may be necessary for me to provide you with a little basic biology.

The Human Cell

    Our human bodies literally contain trillions of individual cells, all possessing vital parts, with specific jobs to perform throughout their “programmed” lifespan.  Each cell contains a nucleus, or control center, which houses the genetic blueprint, providing instructions for everything about YOU. Inside the cell’s nucleus are 23 pairs of chromosomes – totaling 46 chromosomes.  One chromosome of each pair is inherited from your mother, and one from your father. Chromosomes are made up of protein and contain two very long-twisted strands of genetic information known as DNA (deoxyribonucleic acid). Under a very powerful microscope, DNA has the appearance of a double helix, or spiral staircase, containing millions of stairs. Genes are sections of DNA which contain the blueprint or set of instructions, which is passed on to our cells. This information tells the cell to make proteins and everything needed for the body to grow and function, including when to destroy a damaged cell.

Cancer and Genes

One of the functions of our genes is to tell each cell how to replicate itself. Sometimes, a fault can occur in the genetic DNA causing that cell to ‘mutate’. Mutations in our genes can cause cells to replicate out-of-control, which causes cancer. This can occur for many reasons, and very often as a result of something we have been exposed to, such as a carcinogen, virus, toxin, or radiation. Sometimes, life-style risk factors for developing cancer can be shared in families, such as obesity and smoking. We can also be more susceptible to cancer if we have inherited cancer genes from one or both parents. This situation is not as common, and experts believe that only 5-10% of cancers are due to inherited mutated/cancer genes. Not all cancer genes will progress to become cancer, either. If you have inherited an altered gene, that does not mean you could develop ALL types of cancers, rather you may be more susceptible to specific types of cancer, such as breast and ovarian or colorectal cancer. So far, scientists have isolated around 300 different genes that play some role in developing cancer.

Common Types of Cancers Caused by Inherited Genes

Breast and/or Ovarian Cancer

BRCA1 or BRCA2 genes – According to most recent estimates, 55 – 65% of women who inherit the harmful BRCA1 mutation, and 45% who inherit BRCA2, will go on to develop breast cancer by the age of 70 years.  About 39% of women who inherit the BRCA1 mutation and 11-17% who inherit BRCA2, will go on to develop ovarian cancer by the age of 70 years. Scientists who study genes in families have coined the term Hereditary Breast and Ovarian Cancer Syndrome (HBOC). These scientists believe there is possibly a further gene which they have labelled BRCA3, though it has not yet been identified. This is thought to exist since some women and families have HBOC based on cancer history, yet don’t have the mutated genes BRCA1 or BRCA2.

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)

HNPCC is the most common inherited syndrome, which increases your risk of colorectal cancer. It is also known as Lynch syndrome. In Lynch syndrome, one or several mutated genes responsible include MLH1, MSH2, MLH3, MSH6, PMS1, PMS and TGFBR2, and are responsible for DNA repair. Most of the cancers that appear from this syndrome happen before the age of 50. This syndrome can also lead to a high risk of developing other cancers such as endometrial (uterine), ovarian, breast, stomach, small intestine, pancreas, prostate, urinary tract, liver, kidney and bile duct cancers.

Li-Fraumeni Syndrome

This syndrome is quite rare and most often occurs during childhood or young adulthood and is associated with cancers such as sarcomas (osteosarcoma and soft tissue sarcomas), leukemia, brain cancer, adrenal cortex and breast cancer. These cancers are most often caused by the mutated genes p53 and TP53. (The gene p53 normally stops the growth of abnormal cells, and TP53 is a tumor suppressor gene). Don’t be overly alarmed by these statistics, as there are ways to switch cancer-causing genes off! Over the next few articles, we will take a look at these preventative measures, and how to switch these genes off. PLUS genetic testing and the “Jolie Effect”. Stay tuned! References: DNA from the Beginning Cancer Research UK FORCE - Facing Our Risk of Cancer Empowered National Institute of Cancer American Cancer Society Cancer.net Atlas of Genetics and Cytogenetics in Oncology and Haematology