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Hereditary Cancer Public Perception | Cancerbackup August 13, 2007

Posted by ramunas in cancer genetics, familial cancer, hereditary cancer, media, sporadic cancer.

There were recently data released from survey performed by information charity Cancerbackup and Genes Reunited during collaborative What Now? campaign, which is aimed to highlight the myths that exist around cancer and genetics.

This survey reveals the unnecessary worry that exists because people overestimate their cancer risk based on their family history.

Of over 1,000 people that responded to the survey 60% incorrectly thought that family history was the biggest risk factor for cancer and only 15 per cent knew that it is actually age – two thirds of cancer incidence is in people over 65-years-old, says MedicalNewsToday.

I generally look quite carefully to such public surveys and media trends for interpreting results out of context – it is easy to dismiss important findings then.

It is now well established that genetic factors play an important role in causing cancer, therefore arguing that most cancer is non – genetic can be confusive both for public and other health care providers. “All cancer is genetic but some cancers are more genetic than others”. That actually means , that in most cases the causal mutations are not inherited but are acquired somatically, possibly as part of the normal aging process or as a result of prolonged exposure to particular carcinogens. Saying “genetics” does not necessarily means “something inherited”.

The cancer risk perception is a complex and personal feeling, and depends on a family history. Therefore from these (only) 1000 responders there could be a proportion of people with a strong family history, which naturally experiencing higher family history attribution. I remember one of my patient, who came and said – I definitely have a mutation – and she was right, because her mother, maternal aunt and grandmother died of breast cancer in an early age and she was also affected. For families like this cancer family history is really number one risk factor.

Cancer is so common that probably everyone of us has (or had) some relative with this disease. Some common cancers in the family may have occured by chance, but again, age is an important factor, which could indicate that cancer is occurring due genetic predisposition: young age is considered to be <50 years for breast, stomach, pancreas, bowel and prostate. For ovarian cancer, occurrence in an older age is still likely to be significant factor, if there are other family members affected with either ovarian or early breast cancer. Therefore, evaluating family history, the important features suggestive of an inherited susceptibility to cancer are (ref.):

  • early age of onset
  • bilaterality of disease (i.e. multiple primary tumors)
  • multiple cases on one side of the family (two or more first/second-degree relatives):

The vast majority of people realized that it is not just breast cancer that can occur because of an inherited genetic link. However, they didn’t realize that in order to suspect such a link, generally the same type of cancer (or cancers that are known to run together such as breast and ovarian or bowel and womb cancers) would need to occur in family members on the same side of the family (via).

  • other related early-onset tumors (“patterns” of associated cancers, e.g. breast and ovarian, colon and endometrial)
  • rare cancers (e.g. two or more relatives with the osteosarcoma).
  • ethic origin (Ashkenazi, Icelandic, Eastern European, Dutch etc).

Ageing is definitely an important risk factor, and cancer risk increases with age, with the highest incidence occurring over age 65 (64% (64 in 100) of all newly diagnosed cancers occur in people aged 65 years or more [via]). This may be due to less affective immune responses in the elderly or a lifetime of exposures. Probably, a cancer is a natural evolutionary fate of a cell in multicellular organism.

It is important to remember some sobering cancer risk factors (source: Offit, 1998):

  • diet – 35% (mainly alcohol, high protein intake, smoked/curred food, high fat intake)
  • tobacco use – 30% (mouth, pharynx, larynx, esophagus, stomach, lung, kidney, pancreas, bladder, cervix (sic!)).
  • hereditary factors – 5-10%
  • occupational exposures – 5%
  • radiation – 1-2%
  • viruses – 1-2%
  • miscellaneous – 16-23%

Bolded factors (65%) are important modifiable lifestyle factors for general population and tobacco is a single most important avoidable cancer-causing agent. However, the extent to which lifestyle changes can modify the cancer risk in individuals with inherited predispositions to cancer is unclear.

When asked what percentage of cancers occur because of a known inherited genetic link, only 13 per cent of people knew that just 5-10 per cent of all cancers are known to be hereditary. Furthermore, a quarter of people thought that between 50 – 100 per cent of cancers are hereditary (via).

Yes, that is true. But again – there is another type of cancer – familial, which could account up to 30% of cases. For example, up to 27% of breast cancer can be attributed to heritable factors from twin studies. Familial type refers to multifactorial inheritance, implying the interaction of additive polygenes with the environment, and probably plays a role in around 20-25% of cases.

It is important to remember general population risks (Western societies)

  • lifetime risk for any cancer -(1/3 – for women, 1/2 – for men
  • breast cancer (female) – 1/10 – 1/12
  • prostate cancer (asymptomatic) – 1/3
  • prostate cancer (clinicaly diagnosed) – 1/10
  • colon cancer – 1/25 – 1/50
  • ovarian cancer – 1/70
  • proportion of common cancers which is inherited – <1/10.

A staggering 91 per cent of people surveyed in a Cancerbackup poll on Genes Reunited’s website, thought that if one of their relatives had cancer, they are at a greater risk than average of getting it themselves. In actual fact in the majority of cases this would not significantly increase someone’s risk at all.

Again, I would interpret this with caution. Family history is an important risk factor for breast or ovarian cancer.

Although reproductive, demographic, and lifestyle factors affect risk of ovarian cancer, the single greatest ovarian cancer risk factor is a family history of the disease. A large meta-analysis of 15 published studies estimated an odds ratio (OR) of 3.1 for the risk of ovarian cancer associated with at least one first-degree relative with ovarian cancer, cancer.gov claims.

So, a family history of ovarian cancer increases the risk by threefold, which, I think is not so unsignificant factor.

Also, in a pooled analysis of 38 studies, the relative risk of breast cancer conferred by a first-degree relative with breast cancer was 2.1 (95% confidence interval [CI], 2.0-2.2). Risk increases with the number of affected relatives and age at diagnosis.

Textbooks (this and this) states, that the presence of a first-degree relative with breast cancer increases the risk 1,5-4.0-fold, depending on the age of the affected family member.

Having one affected first-degree relative increases the risk of colon cancer by three- to fourfold and having several relatives with colorectal cancer may be consistent with a hereditary cancer syndrome, Katherine Schneider writes.

Obviously, one or two cases of cancer in a family does not necessarily mean that there is a hereditary cancer syndrome in that family, but familial cases are also important to distinguish.

In conclusion, patient concern for cancer is common and valid reason for referral to genetic counseling. About 60% of women are referred to a familial breast cancer clinics due to their own initiatives. It was already shown, that from clinical attendees with a family history of breast cancer in UK, only 25% belonged to high risk, 25% had population level or lower risk, and 50% reached sufficient risk level for screening. “A women who has a low risk of being cancer-prone, but who is worried by her family history, should have access to consultation”, Eisinger et al. states. Often risk assessment alleviates fear and anxiety. Genetic counseling and testing generally results in lower psychological distress, both for those individuals who test negative and those who test positive.

Dr. James Mackay, Clinical oncologist and medical director of Opaldia, a private UK genetic testing company, and scientific advisor for a private polish genetic testing company Read-Gene, highlights some important questions of cancer genetics, which I’ve found in Cancerbackup YouTube account:

Anyway, I’ve missed more opinions of other independent clinical cancer geneticists, especially from academical setting.



1. AC - August 14, 2007

You’ve been tagged: The Bayblab is proud to host the first ever blog carnival on cancer research. A blog carnival is an event where a community of bloggers come together to explore a common subject of interest. Not only does it create a tool to exchange ideas, but it is a good way to exchange links and increase readership. The rules are simple, write a post about any aspect of cancer research, for example where you see your field contributing to cancer treatment in the future, and submit a link to your story to the comment section of this post (http://bayblab.blogspot.com/2007/08/cancer-research-blog-carnival.html) by August 24th. Also, please copy and paste this message to the comment sections of as many relevant blogs as you can. Let the fun begin!

2. Frances Palmisano - September 2, 2007

Young single mothers are just like any other teens. They eat poorly, sometimes drink, or smoke. They’re influenced by peer pressure to become sexually active and then when they become pregnant, those same influences can be damaging to her child. After the baby is born a young single mother and friends may part ways. The mother may face alienation and ridicule from the same friends that helped to influence the same behavior that got her in trouble.


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