Can cancer be caused by bad luck?


A recent study claims that “bad luck” may be responsible for two thirds of the total risk of cancer. Renowned oncologist Professor Luis Costa takes a closer look.

A research analysis by Professor Luís Costa

We have all heard of these cases. The non-smoker who develops lung cancer. The daily hat and sunscreen wearer who gets skin cancer. We have also heard about people who unexpectedly find themselves facing a more uncommon cancer diagnosis, without any possible explanation based on family history or exposition to carcinogens. When speaking of these cases, we often say that such a person has “good” or “bad” genes.

Yet a recent study from Johns Hopkins Kimmel Cancer Center in the United States, now claims that what we have attributed to genes might actually be a matter of luck. Indeed, the study has created a statistical model that shows that “bad luck ” is responsible for two thirds of the total risk of cancer, with just one third attributed to genetic and external factors, such as lifestyle.

Many people have misunderstood this to mean that luck is a cause of cancer in itself, which is not the case. The probability of developing cancer is strongly linked to three major factors:

  • exposure to carcinogenic agents (e.g. tobacco, poor diet and viruses such as hepatitis B)
  • genetic predisposition
  • the number of stem cell divisions in a specific tissue during a person’s life-time

Stem cell division, or replication, is when DNA mutations may occur. These mutations are what can consequently develop into cancer. What the Johns Hopkins study points out is that stem cell division, is probably the most relevant for the majority of cancers. So what the study is referring to is our good or bad “luck” that a particular body will part undergo less or more cell division over time.

The cancer “car accident”

In explaining their findings, the study’s authors compared the risk of getting cancer to the risk of having a car accident.

the length of your trip = your lifetime

weather conditions = external factors, such as tobacco, viruses, lifestyle

the condition of your car = genetic factors

There is no one cause of cancer. What the study points out is that we cannot change the road we travel from A to B, just as we cannot do anything about the length of our life and the number of stem cell divisions our body will undergo in its various parts. However, we can avoid driving in bad weather and we can take our vehicle in for regular inspections, the same as we can avoid things like tobacco and poor lifestyle choices, speak to our doctor about genetic testing if we have a family history of cancer and adopt preventive measures if we are found to be at risk.

Insight for doctors

The study shows that, by calculating the “extra risk score”(ERS) as the product of a person’s lifetime cancer risk and the total number of stem cell divisions, we, as doctors, can propose a more tailored approach to primary prevention (pre-emptive measures) or secondary prevention (early detection) according to tumour type.

All tumours work differently, and in the study the so-called D-Tumours (those with a high ERS score, such as lung cancer in smokers) are those which may be influenced by external risk factors. For these, primary and secondary prevention could have a major impact. On the other hand, the R-Tumours (those having a low ERS score, such as lung cancer in non-smokers) are more likely to benefit from secondary prevention only. This is why early detection is so fundamental.

Not all tumour types included

Finally, it is important to point out that the Johns Hopkins study did not include certain cancers, such as breast and prostate cancer, which are two very common cancer types. This is possibly due to the fact that in breast cancer and prostate cancer, tumour development is strongly linked to hormonal factors. Perhaps this dependence on hormonal factors signifies that the link between the number of stem cell divisions in breast tissue or in prostate and cancer incidence in these organs is not clear.

Professor Luis Costa is Director of Oncology at Lisbon’s Hospital de Santa Maria and a member of the Best Doctors European Medical Advisory Board.

To read more about the study, please see:

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