Should You Get Your DNA Tested to See if You're More Likely to Get Cancer?


If the future were knowable, would we want to know it? When I was young, a fortune teller who predicted several things in my life that subsequently came true predicted my age at death. At the time it seemed an eternity away, so I thought no more of it, but now it is not so very long away at all. If I were more disposed to believe the fortune teller’s prediction than I am, would I use my remaining years more productively or would I be paralyzed with fear?

In a recent edition of the New England Journal of Medicine a question was posed about a 45-year-old man in perfect health (insofar as health can ever be described as perfect) who asked for genetic testing about his susceptibility to cancer, given a fairly strong family history of it. Should he have his genome sequenced?

A geneticist answered that he should not: to have his entire genome sequenced would lead to a great deal of irrelevant and possibly misleading information. But if the family history were of cancers that themselves were of the partially inherited type – more factors than genetics are involved in the development of most cancers – then the man might well consider having the relevant part of his genome, namely that part with a known predisposing connection to the cancers from which his family had suffered, sequenced.

This is not a complete answer, however. Two obvious questions arise: is additional risk clinically as well as statistically significant, and if the risk is known can anything practicable and tolerable be done to reduce it? There is no point in avoiding a risk if to do so makes your life a misery in other respects. You can avoid the risk altogether of a road traffic accident or being mugged on the street by never leaving your house, but few people would recommend such drastic avoidance.


When people tell you that something x causes a twofold increase in the risk of y, you need the absolute as well as the relative risk in order to know whether it is really worth avoiding: for on the absolute size of the risk depends the effort that it is worth making to avoid it. Moreover, you also need to know the size of the risk-reduction brought about by the avoiding action, and again the absolute as well as relative figures are necessary to make a decision.

As if this were not complex enough, people vary so much in their values that it is usually not possible to give unequivocal advice. A risk that seems to one person to be worth going to enormous lengths to avoid may be deemed trivial by another. No one can speak for anyone else.

Then there is the question of cost. Who is paying for the tests? Rarely nowadays do people pay directly from their own pockets for their own care, but rely rather on third party payment. The third parties then pass on the costs to others. Is this fair in the majority of cases in which the results are of uncertain benefit even to the person on whom they are performed?

No wonder most of the commentary after the article was published was negative. Quite a few doctors expressed almost fatalistic attitudes, such as that we all have to die sometime and it is best not to peer into the future, especially if, knowing it, or rather knowing the statistical chances of it, we in the meantime make ourselves miserable. Sufficient unto the day is the illness thereof.

Oddly enough, however, and despite the negative commentary, the majority of doctors who voted on the question thought that the 45-year-old man ought to undergo some kind of genetic testing: just in case, I suppose.


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