[jamest (OP)]

Van writes in with, 'A friend is encouraging me to take a cancer screening test that screens for many different cancers. I read about one test: "While overall it picks up 90% of stage 4 cancers, it only detects an average of 17% of stage 1 cancers. Yet it is being touted as a test that can detect cancer early." Are these tests worthwhile?'

[paul cotter]

They all vary in efficacy. Stage 1 is obviously what one wants or even better precancerous lesions with stage 4 often being a death sentence. The PSA test for men is moderately effective but still can produce false positives and false negatives with a false positive having the danger of unnecessary medical interventions. Overall I think if one has a family history of a particular cancer then screening for this particular cancer is a good idea. Personally I am 72 and I get a PSA test yearly and that is the only screening I partake in- there is a family history of lymphomas but no screening test to detect it early that I know of. NB: I am not a medic and you should seek professional medical advice if you have a problem.

[alancalverd]

The "worried well" constitute a soft and growing market.   

The phrase "many different cancers" strikes a warning note. In civilised countries (i.e. everywhere except the USA) the national health service offers screening of known beneficial sensitivity and specificity for particular conditions for which there is effective treatment. Where there is a known individual family history, general practitioners will recommend additional and appropriate tests.

a test that can detect cancer early.

"Can" is very different from "does". Depending on the target disease, the invasiveness of the test, and the effectiveness of treatment, I would be very wary of any test with less than 90% sensitivity (ability to identify true positives) and specificity (ability to rule out true negatives) unless I had symptoms or family history. And now being well beyond my "use by" date, I probably wouldn't bother anyway.

[Bored chemist]

There's nothing special about cancer tests.
Any test - even if it's the tensile strength of a ball of wool or the alcohol content of your home brew- is only useful if there is something you can do with the result.*

If some test tells you that you have a more that 10% chance of having (for example) pancreatic cancer, what do you do with that information?

If you can get an MRI scan or whatever to check, that might be useful.
But there probably aren't enough MRI machines for everyone to get scanned for all the (probably mainly false) positive test results.

So the only real outcome for most people (who can't buy their way to the front of the queue at the scanner) is increased worry.


*  This isn't strictly correct. I worked in a chemistry lab for ages so I know  the other use of a test is "selling it to other people".

[alancalverd]

But there probably aren't enough MRI machines for everyone to get scanned for all the (probably mainly false) positive test results.

The companies I work for are installing MRI units at the rate of about one per week, half in the NHS and half in the private sector (usually supported by an NHS contract).  Problem is that there aren't enough radiographers to staff them (it takes 4 years of training) and although thanks to wonderful, expensive, near-compatible and occasionally functional  digital technology we can get the scans reported overnight, there aren't enough surgeons/oncologists/nurses/linacs/operating theaters/techologists/hospital beds to do anything about the findings.

Apropos probabilities, we can confidently state that any 50-year-old in the First World has a 50% probability of developing a cancer of some sort, and half will be fatal, so there's little point in testing with less sensitivity.

[Bored chemist]

we can confidently state that any 50-year-old in the First World has a 50% probability of developing a cancer of some sort, and half will be fatal, so there's little point in testing with less sensitivity.

You and I might be over 50, but quite a few people aren't.

[alancalverd]

The figures are lower for younger people because they have a greater probability of dying from something other than cancer (infection, accident, suicide......) before they reach 50.

Fact is that cancer accounts for around 25% of all deaths in the UK because most people live long enough to express a fatal tumor. But where life expectancy is significantly shorter (Russia, most of Africa...) the figures are very different. For instance Nigeria, with a population of ~200,000,000 and life expectancy of 55 years, reported only 70,0000  cancer deaths in 2018, less than a tenth of the corresponding number at UK rates of incidence.

[vhfpmr]

When I had my bowel tumour, the FOB test was negative even after I'd already seen blood in the toilet.

[alancalverd]

Good point! Screening may be indicative, but symptoms are definitive.

[paul cotter]

I would be fairly sure that particular test produces a lot of false positives. All you have to do is scratch your butt a bit in cleaning or a hard constipated dump, either of these could give a false positive.

[vhfpmr]

Has anyone ever looked at whether increase in PSA is more reliable than absolute PSA level?

[alancalverd]

The interpretation of and subsequent action from PSA tests are frequently uncertain. What is known is that  many men die with, but not from, benign prostate hypertrophy, or even prostate cancer. Signs and symptoms are not quite the same thing.

[paul cotter]

Yes, indeed you are correct, Alan. Post mortems on elderly men frequently indicate cancerous lesions in the prostate. Some prostate cancers seem to be quite slow and do not reduce life expectancy. Benign prostatic hyperplasia is extremely common(touch wood, not me , yet!).

[Bored chemist]

Obviously, the amount of faith you put in a PSA test might depend on how far from normal the results are.
I went to the Dr with relatively mild symptoms.
PSA over 400 (should be less than 4.5 for someone my age)
Metastatic prostate cancer.
With luck, drugs and radiotherapy, I might have another 5 years.
I'm not yet 60 years old.

It's impossible to know what difference regular screening would have made but... maybe I'd be due to reach state pension age.

[Eternal Student]

Hi.

    I'm sorry to hear that @Bored chemist  .     
There's a lot of treatments and different people repond differently.  We genuinely just don't know how long we've got.   

I don't suppose there's a lot I can say that you haven't already been told or researched for yourself.   Just assume I've said all the usual stuff and I'm sure everyone else that you've helped on the forum would also say it.

The good news is that you'll be on the forum for years.

(The very best of) Best Wishes to you.


     

[paul cotter]

I am lost for words, I was not expecting a seemingly theoretical discussion to turn to tragedy.  As ES has noted, however, huge strides are currently being made in oncology and previously incurable conditions are falling to treatment at an ever increasing rate. Obviously I wish you the best and if by any chance there was anything I could do for you, just ask.

[Bored chemist]

It's a pity, but not a tragedy.
We all go. I have a better idea than most about when my time will be up.
If I'm lucky, someone will find a cure but the odds are against that.


And I'm lucky enough to have retired early so I have some time to mess about with nerdy stuff.
If my pension fund only has to last as long as expected then I'm fairly wealthy.
If I last l until I get my state pension , then I don't need to worry about funding.

So, at least on that score I'm OK and, at the moment most of me is fine.

But the point remains that, with a comprehensive screening programme, I might be looking at a different outlook.
Of course there might be ten other guys who, having found they had a marginally raised PSA would have  worried themselves into an early grave over nothing. Or there might be 20 people who went short of good A&E care because the money got spent on PSA tests that confirmed that very few asymptomatic middle aged men have prostate trouble.

The question of testing for cancer doesn't exist in isolation.

[Billy Fisher]

I?ve looked into these multi-cancer screening tests because cancer runs in my family, but I?ve been hesitant for the same reason?early-stage detection rates are pretty low. They seem more useful for picking up advanced cancers, which kind of defeats the "early detection" selling point. Personally, I?ve stuck with the standard screenings like colonoscopies and mammograms since they?re more proven. If you?re in a high-risk group or really concerned, it might be worth discussing with your doctor, but I?d be cautious about putting too much faith in these tests just yet.