Check Up #8 - Familial and hereditary cancer

All cancers are genetic in nature, in the sense that they all arise from genetic mutations inside cells. But the origin of those mutations can vary: they can be due to environmental factors (for example exposure to carcinogenic substances such as tobacco smoke or asbestos particles), but also to spurious DNA replication errors during the cellular division of any cell type in the body. Such random, unpredictable DNA errors account for nearly two-thirds of the mutations responsible for cancer. Lastly, cancers can be due to genetic mutations transmitted from parents to their children through the father’s sperm or the mother’s ovocytes (the germline cells). These are hereditary cancers.

Only about five percent of all cancers are hereditary cancers. Some cancers that can be hereditary are breast cancer, colon cancer, prostate cancer, ovarian cancer, uterine cancer, melanoma, and pancreatic cancer. But that doesn’t mean that a cancer will certainly develop in the individual who inherited a cancer-causing mutation in a gene; it just means the individual has a predisposition to develop that type of cancer – that is, that he or she has a higher risk than most people to develop it. More than 50 genes involved in cancer predisposition have been identified.

Maybe one of the most mediatic hereditary genetic mutations are those found in two genes called BRCA1 and BRCA2, which are responsible for hereditary breast and ovarian cancers. They were much talked about a few years ago, when the actress Angelina Jolie decided to have total breast and ovary tissue removal after learning that she had a BRCA1 mutation (three women in her family had died of these inherited cancers).

Identifying families with possible hereditary cancers is very important, because family members can then benefit from efficient measures, such as early detection and even prevention. 

But what about people who have a number of relatives who had cancer? Have they necessarily inherited faulty genes from their parents? The answer is No. Familial cancers are not always hereditary. Far from it.

There are ways of distinguishing hereditary and non-hereditary cancers when they seem to run in the family. For instance, if cancers in a family did not develop at younger ages than is normally expected, chances are that they are not due to inheritable genetic defects. And if the relatives who developed cancer had different common types of cancer in different organs, were distant relatives or from both sides of the family, the same conclusion applies.  
  
Also, given that about one in three people in developed countries will have cancer during their lifetime, it is not uncommon to have a number of cancers in a family. Moreover, cancer might be more common in certain families not because of inherited faulty genes, but because of shared lifestyles and environments – smoking and obesity, for example, are known to be high-risk factors for cancer.

Sources:

https://www.cancer.org 
https://www.cooperhealth.org
https://www.cancerresearchuk.org
https://www.yalemedicine.org
https://www.hopkinsmedicine.org
https://www.cnio.es/
https://www.genomemedical.com

By Ana Gerschenfeld, Health & Science Writer of the Champalimaud Foundation.

Reviewed by: Professor António Parreira, Clinical Director of the Champalimaud Clinical Center.