By Dr. Tarang Lad

Hereditary Aspects Of Cancer

Cancer is a multifactorial genetic disease. Here multifactorial means, cancer can be caused by more than one gene. Which clears that it has polygenic mode of inheritance, depends upon a number of genes at different loci (region) on DNA. Age and environmental factors may produce some influence on these genes to develop cancer in some people. So inheritance of cancer is a combine effect of genetic as well as environment.

Genetics includes genes and heredity. Genes and DNA are the genetic material present in our body cells. Cells are the basic functional and structural units of our body. To perform the function properly cell needs to grow. So they under go cell division. Heredity involves the transmission of genetic material from parents to their offsprings (children). This transmission can happen through cell division. DNA present in the cell contains thousands of genes and each gene is a set of instructions for something specific, like our hair color, eye color, height etc. Some genes control growth and division of cells. If some harmful change(mutation) occurs in these genes they cannot perform their function effectively, so cell grows uncontrollably. This uncontrollable growth of cell forms lumps or tumor that we know as cancer. This change or mutation may occur by mistake happen during cell division or from a damage caused by mutagens for example chemicals, radiations, sun exposure etc.

We have two types of cells one is somatic that is present in all over body and other type of cells are germ line cells which are egg and sperm cells present in reproductive organs. Changes in somatic cells cannot be passed from parents to their children. So in this condition any mutation that is causing cancer occurs in somatic cell of a person it remains in that particular cell and tumor in only. It is not present in the each and every cell of the body. These mutations are known as acquired mutations. Here acquired means arises due to the response of the particular cell to the environmental factors / mutagens. Although reason behind it not known. This type of cancer is known as Sporadic Cancer. That means it is just a chance event and is not hereditary. Most of the people who have cancer come under this category. If several members of a particular family are affected with sporadic cancer it might be just by chance.

Sporadic cancers are caused by aging, life style and environment not by genetic risk factors. Doctors generally look for gene mutations in cancer cells, which is important for treatment and prognosis. However in sporadic cancers, the gene mutations are acquired, as we already know, therefore the relatives of an individual who has sporadic cancer will not have the same cancer causing genes. People with sporadic cancer in families have an average chance of getting cancer themselves and can follow the usual recommendations for cancer prevention and monitoring.

Though we have not identified genetic cause of all type of cancers but we do know several gene changes (mutations) that can pass from parent to children and can increase a persons risk of developing cancer. these changes are known as hereditary cancer syndrome. Here hereditary means diseases ( cancer) with known genetic cause. A small group(5%-10%) of families have this type of cancer. In these families there is a strong inherited risk factor for cancer. Most of the hereditary cancer is associated with a germiline mutation. This can be entered in the zygote via egg and sperm cells, and then consequently present in every cell of that particular person. So the first step in the development of cancer has already been taken in every cell. In normal inheritance we get one complete copy of our genes from mother and another from father. So if we get one mutated copy, also known as susceptible gene, and one normal copy of gene. In this condition normal copy of gene will help cell to work properly. However if any mutation occurs in working copy then cell looses its growth control and become cancerous. Therefore individual with susceptible gene has much greater chances of developing cancer in their life time than the individual who does not have the susceptible gene.

A family history of cancer may impact risk of developing cancer even if an inherited mutation is not present. This type of cancer is known as familial cancer. So cancer can be considered familial when two or more relatives are diagnosed with cancer, specially the same type of cancer. Although very little is known about the reason of cancer family clustering. But possible reason might be minor DNA changes that are not the part of hereditary cancer syndrome, interacts with environmental influences. So shared environmental or life style factors such as exercise, diet or tobacco in family may impact the cancer risk. There are two tools available to identify people with hereditary cancer. First one is family history and the second one is genetic testing. In family history genetic counselors takes complete information about the cancer history of the family. For that some points are find to be important like When the family has had cancer, what kind of cancer they had, how old they were when they develop cancer. Genetic testing is done with blood sample and saliva sample to know the specific gene mutation associated with cancer. It is important to use both family history and genetic testing together because each of them give us different kind of information, by putting them together we can have the most accurate picture of someone’s chances of getting cancer.

Sporadic cancer develops at later age. In this case cancer in the family affects a few people. All members in the family who get affected by the cancer will develop different kind of cancer. While hereditary cancer develops in young ages. More than one type of cancer can be seen in one member. Same type of cancer like breast cancer and ovarian cancer or colon cancer and ovarian cancer can be seen. Rare cancer like ovarian and fallopian tube cancer or breast cancer in men can also be seen in hereditary cancer. Because very few families have all these features when we see some of them for hereditary cancer we can go for genetic testing.

In both the cases sporadic as well as hereditary cancer syndrome genetic testing helps to decide the treatment and prognosis. Like breast cancer can be diagnosed through triple negative testing. We have some good medicines for genetic mutations like Olaparib, which works very well in controlling breast cancer. sometimes it can even eliminate the breast cancer. Immunotherapy works very well in Lynch syndrome, even if it is stage 4 cancer. The cancer could be eliminated completely. It is always good to know the genetic inheritance of cancer even after the treatment for follow up. If it is a non-genetic cancer routine follow up with minimal check ups can help to know if disease has relapsed. But if the patient has genetic inheritance then multiple MRIs, multiple tests, frequent check ups are mandatory. Because relapse of cancer is quiet possible even after the treatment as the person has the cancer causing genes. It is also good for relatives to know the genetic inheritance of the cancer patient. If it is hereditary the close relatives can go for testing for the same. As we all know that it is good to know about cancer in early stage because it is curable.

Genetic testing is not a test that one can easily do in normal path lab by simply giving the samples. Pre test and post test counseling with genetic counselor for this is required. Because results does not show simple positive or negative result, it has some scientific language, so genetic counselor needed to interpreted it. So one should not do it by their own.

*disclaimer; don’t use any medicine without doctors permission