Three Generations of Cancer: Draw the Family Tree

If there is three generations of cancer in my family and you are wondering what to do about it, the single highest-value action is smaller and more practical than you might expect. Draw the family tree. Set out who was affected, by which cancer, and at what age, across the generations you know about, and take that one page to your GP. A drawn family history — a pedigree — is the thing a doctor can actually read a risk from, and it is worth far more than a worried sentence in a ten-minute appointment.

Most people carry this as a vague dread: cancer keeps appearing, it feels like a pattern, and they do not know whether it is bad luck or something inherited. A pedigree turns that fog into information. It shows at a glance whether the cases cluster on one side of the family, whether they struck unusually young, and whether the same type of cancer recurs — the three features that separate coincidence from an inherited pattern a clinic should look at.

This page shows you how to draw a family tree properly, what your GP does with it, and what a clinical genetics service does next if the pattern warrants a closer look.

The short answer: draw it, then take it to a GP

Cancer is common, which is exactly why a family pattern is hard to read from the inside. Most people have several relatives who have had cancer at some point, and the great majority of that is not inherited. What a clinician is looking for is not the raw fact that cancer appears in your family, but its shape: how many relatives, how closely related to you, how young, and whether the same cancers recur on the same side.

You cannot judge that shape by feel, and neither can a GP across a hurried conversation. A pedigree lets both of you see it. It also does something quietly important: it forces you to gather the details — sites and ages — that turn "lots of cancer in the family" into a pattern a referral system can act on. The drawing is the work. Once it exists, the medical steps are straightforward.

How to draw a three-generation family tree

You do not need software or medical training. A large sheet of paper and a pencil will do. Work across three generations where you can: your own (you, brothers, sisters), your parents' (parents, aunts, uncles), and your grandparents'. Keep the two sides of your family clearly separate, because an inherited risk usually travels down one side, and mixing them hides the very pattern you are trying to reveal.

For every person on the tree, try to capture the same set of facts:

• Their relationship to you, and which side of the family they are on.
• Whether they are alive. If they have died, their age at death and the cause.
• If alive, their current age.
• Any cancer they were diagnosed with, and — this is the detail that matters most — the exact site. "Bowel", "breast", "ovary", "prostate", not just "cancer". Two different cancers in a family mean something very different from the same cancer twice.
• Their age at diagnosis. Young ages carry more weight than old ones.

Clinicians use a standard notation — squares for men, circles for women, a line through the symbol for someone who has died — but you do not have to. A clearly labelled list or a rough tree that captures the facts above is enough for a GP to work with and to redraw formally if it goes further. What counts is the information, not the artistry.

Why both sides, and the unaffected relatives, matter

Two instincts lead people to draw an incomplete tree, and both weaken it. The first is to record only the side where the cancer seems to be. But you often cannot tell in advance which side carries a risk, and some inherited cancer syndromes affect organs people do not connect — a gene linked to breast cancer can also raise ovarian or prostate risk, for instance. Draw both sides fully and let the assessment find the pattern.

The second is to leave out the relatives who were never ill, as if only the cancers count. They count too. A clinic reading your tree needs the denominator: two affected relatives among four siblings is a very different signal from two among a dozen. The unaffected people, their ages, and how many there are give the affected cases their context. A tree that lists only the diagnoses overstates the pattern; a complete one lets it be judged honestly.

Where you simply do not know — a branch you lost touch with, a grandparent whose illness was never named — record that too, as unknown. An honest gap is useful information, and no one expects a perfect tree. People who were adopted, or who cannot reach half their history, face this squarely, and "not known" is a legitimate entry rather than a failure.

What your GP does with it

Your GP is the gateway to everything that follows, and the pedigree is what lets them decide whether you cross a threshold. They will look at the pattern — numbers, relationships, ages, sites — and weigh it against referral criteria. Most people who bring a family history are, reassuringly, below the threshold for specialist referral, and being told that your pattern does not suggest an inherited syndrome is a genuine result, not a brush-off.

Where the pattern does meet the criteria, the GP refers you on — to a regional clinical genetics service or, for some cancers, a family history clinic run by the relevant specialty. They may also arrange or bring forward ordinary screening in the meantime. This is why the drawn tree earns its keep: it converts your worry into the specific evidence a referral decision needs, and it means the referral, if it happens, arrives with the information already attached. You can read more about how the NHS approaches this on the NHS page on genetic and genomic testing.

What a clinical genetics service does next

A clinical genetics service takes the pedigree, verifies what it can — sometimes confirming a relative's diagnosis through records, with consent — and assesses your risk against national criteria. Those criteria come largely from NICE, which sets the clinical thresholds the NHS uses to decide who needs closer attention. The assessment turns your family tree into an estimate of your own risk, and there are broadly three places it can lead.

The first is reassurance: your pattern is within the range explained by chance and common risk, and you continue with the ordinary screening everyone is offered. The second is extra surveillance: earlier or more frequent screening than the general programme, because your risk is raised but no single gene is implicated or being tested. The third is genetic testing. Crucially, testing usually starts not with you but with an affected relative, where one is alive and willing, because finding the specific fault in someone who had the cancer tells the clinic what to look for in you. If a fault is identified, relatives can then be tested for that exact fault — a process that can rule you in or, just as importantly, out.

How a family history is defined for these purposes is not the same as how an insurer defines it, and the gap catches people out. We set the clinical threshold beside the underwriting one in our piece on the two definitions of a family history of cancer, so you can see whether your pattern crosses one, both or neither.

While the referral works its way through, it is worth keeping the fear in proportion, because a family tree with several cancers on it looks more alarming than the underlying odds usually justify. Most cancer is not inherited, even when it clusters in a family, and the biggest driver of cancer risk for almost everyone is simply age rather than genes. The same instinct that makes a pedigree look like fate also makes people misread mortality figures — a point we take apart in why a period life table will not tell you whether you will reach 85. If your worry is broader than cancer specifically, it can help to see what actually kills men in their fifties in the UK, where the leading causes turn out to be the ones with the clearest, most modifiable levers attached.

Does asking for a referral affect my insurance?

This worry stops some people from seeking an assessment, and it should not, because it rests on a misunderstanding of the rules. A referral, an assessment, and any surveillance arranged as a result are medical facts. If a life insurance application asks about investigations, appointments or screening, those are answered honestly like anything else in your notes. That is ordinary disclosure, not a penalty for being careful about your health.

The genetic test result itself is treated quite differently. Under the industry Code on Genetic Testing and Insurance, a predictive genetic result — one taken when you have no symptoms, to estimate a future risk — cannot be requested or used by a UK life insurer, whether it came from the NHS or, as many people now find, from a shop-bought kit. We explain how that protection works, and where its edges are, in our guide to whether a 23andMe result affects UK life insurance. The practical upshot is that fear of insurance is a poor reason to avoid an assessment that could genuinely change your care — and if the family history has made you want cover in place for the people who depend on you, an FCA-authorised broker can compare life insurance quotes across insurers, who weigh a family history differently from one another.

Scotland and Northern Ireland

The approach to family history is broadly consistent across the UK, but the services that deliver it are organised nation by nation. Regional clinical genetics services and family history clinics operate separately under NHS Scotland, Health and Social Care in Northern Ireland, and NHS England and Wales, and referral routes and waiting times differ between them. The criteria used to judge a pedigree are similar in substance, but ask your GP how the pathway works where you live rather than assuming an English route applies.

Wherever you are, the first step is the same and it is yours to take: draw the tree, take it to your GP, and let the pattern be judged by someone equipped to judge it. If you want the wider context of how family history, screening and honest disclosure fit together, our guide to family history, inherited risk and the odds gathers it in one place.

Frequently asked questions

How do I draw a family tree for a genetics referral?

List relatives on each side separately, giving for each the relationship, whether they are alive, their current age or age at death, any cancer diagnosed, the exact site of that cancer and their age at diagnosis. Both sides matter, and so do relatives who were never affected, because they give the affected cases their context. A clear labelled list is enough; it does not need formal notation.

What does a clinical genetics service do with it?

It assesses the pattern against NICE criteria in order to estimate your risk. That can lead to reassurance, to extra surveillance such as earlier or more frequent screening, or to genetic testing, which usually starts with an affected relative where one is available to be tested, because finding the specific fault in them tells the clinic what to look for in you.

Does asking for a referral affect my insurance?

A referral, an assessment and any surveillance arranged are medical facts, and can be disclosed if an insurer asks. The predictive genetic test result itself cannot be requested by a UK life insurer under the industry Code. Fear of insurance is a poor reason to avoid an assessment that may change your care.