Thursday, December 03, 2009

Cancer statistics

It is probably easier to lie with statistics than in any other way. If you put a number to your lie and draw a graph you bully people into believing you. The truth is that many people are afraid of figures.

That is what is currently happening over health service statistics. Let us consider the case of cancer survival. It seems as though it should be simple to compare whether patients with cancer who attend different hospitals survive for longer or shorter periods. If you look carefully you should be able to find out what is wrong with the system and put it right.

Recent statistics demonstrate that the UK is doing particularly poorly when it comes to cancer patients surviving the first year. There are several possible explanations. One is that NICE prevents patients getting access to the latest drugs that would help people to live longer. Another possibility is that the European Working Time Directive, which restricts junior doctors' hours to 48 hours a week means that our surgeons and oncologists are not properly trained when they are let loose on the public. Or it could be that we have too many immigrant doctors, whose training is not up to Western standards, but because of political correctness we cannot say so. Or perhaps it is the nurses' fault, or the managers', or the government's.

But generally I find that when there are marked differences it is because we are comparing apples and oranges.

Although we have quite good measurements for when a patient dies of cancer, we have pretty poor measurements of when a patient contracts cancer. I say quite good measurements of deaths, because quite a lot of patients with cancer die undiagnosed, especially among the poorer members of the community. If you can't afford healthcare insurance then you don't seek out a physician for minor symptoms. You certainly don't buy into executive screening programs. How do you get diagnosed? You die and during your terminal illness your cancer is diagnosed. Or not. This lack of medical attention can have two effects. If you are diagnosed, the diagnosis is too late and you make the figures worse, but if you aren't diagnosed, then you don't get into the cancer statistics which are consequently improved.

Because we don't know when cancer starts, people who are picked up earlier in their cancer journey have better survival figures than those who are diagnosed late. Their longer survival may have nothing to do with better treatment and everything to do with being picked up earlier in the natural history of the disease. One sure way of diagnosing people earlier is by cancer screening of well people. Take prostate cancer. Routinely measuring serum PSA will pick up most cases of prostate cancer (not all because some cancers don't secrete very much). Of course it will also pick up a lot of people with benign enlarged prostates, who will have to undergo an unnecessary prostate biopsy. It will also diagnose many patients who have a well differentiated, slowly growing tumor which would not have presented clinically in the patient's lifetime. These patients will have long survivals, though if they are treated they are exposed to the hazards of treatment that include incontinence and impotence.

It follows then, that if you want to improve your one-year cancer survival statistics you should be a hawk for screening, even though this might not be the best way to benefit patients.

The same is probably true also for breast screening with mammograms. We know that patients are picked up earlier in the natural history of the disease; we do not know that it saves lives. Regular chest X-rays for lung cancer, gastroscopies for stomach cancer, colonoscopies for bowel cancer all have the same result. Does early diagnosis mean that cancer patients live longer? Certainly they live longer than patients who are diagnosed late, but do they live longer than they would have done had their cancer not been diagnosed? The answer is surely yes for some types of cancer, but it is not a given for all types.


Dissenter said...

This seems counter cultural but needs saying. Pick up earlier cancer cases,even if they are never going to cause ill health, and the survival figures look better, even of the day of death is ot postponed. May 2012 is a year later than May 2011 but 2 years later that May 2009, but it is still the same moment in time.

I am sure this is happening in the USA with prostate cancer.

I am promoting dermoscop for the earlier diagnosis of melanoma skin cancer, whcih kills 2,000 people a year in Britain. The establishemnt tends to deride and ignore this technique as 'there's no evidence', but you only get evidence when someone does a trial, and you nly get a trial when someone has the motive and funds to do one. Big trials are expensive, and when nobody has a potentially profitable drug to market, funding is hard to come by.

Also, while removing early melanomas is believed to prevent them from developing into invasive disease, of course nobody has done a proper study, since it would be unethical (and you'd get no informed consented volunteers) for a study to wait and see what suspected early melanomas did if untreated.

So we will have to continue to rely on wisdom, that despised (as contested and hardly subject to measurement) but surely worthy value.

Brian Koffman said...

"Lies, damn lies, and statistics" Benjamin Disraeli

I think some time with our diagnoses we only give patient more years of worry, not more years of life.