Screening programs must show clear benefits

Rinckside 2002; 13,2: 5-7.

 hen I was a schoolboy, all pupils went on an annual excursion to the city district's public health building to be screened for tuberculosis. By the mid-1970s, when I started working in a Swiss hospital, I still had to undergo a chest x-ray for signs of TB.

The Ninth Report of the World Health Organization (WHO) Expert Committee on Tuberculosis published in 1974, however, considered mass radiography a very expensive screening procedure for TB, even in areas of high prevalence. The committee listed additional disadvantages of x-ray screening, saying it:

   contributed only to a small proportion of cases found;
   had no significant effect on the occurrence of subsequent smear-positive cases, which usually develop so rapidly that they arise between rounds of mass radiography examinations;
   required the services of highly qualified technicians and medical staff, who could be better employed in other health service activities; and
   relied on apparatus and transport vehicles that were often out of service.

The authors concluded that the policy of indiscriminate TB case-finding by mobile mass radiography should be abandoned [1]. Mass TB screening with radiography was slowly phased out in most countries during the late 1970s and early 1980s. After all, TB seemed no longer to pose much threat.

   Today, screening is recommended to detect high blood pressure, to monitor height and weight, to assess problem drinking, to measure total blood cholesterol in men aged 35 to 64, and women 45 to 64, and to check for vision and/or hearing impairments in men and women over 65. Pap smears, fecal occult blood testing and sigmoidoscopy for men and women over 49, and, last but not least, mammography for all women aged 49 to 70 are also advocated [2].

Screening is meant to detect early indications of disease in an asymptomatic population. The goal is to decrease morbidity and mortality. Some people like to rephrase this definition. They say that saving lives by screening healthy people for cancer and other diseases is one of the most widely held beliefs in preventive medicine.

The idea of screening and spotting disease before it damages or kills a person is attractive and fascinating. It is a scientific and intellectual challenge, and the sky seems to be the limit with today's technologies. Yet, as Brawley and Kramer point out, the case for screening is not straightforward:

"While screening can potentially save lives, and has been shown clearly to do so in the case of breast, cervical, and colon cancer, it is also subject to a number of biases, which can suggest a benefit when actually there is none, or even mask a net harm. Early detection does not in itself confer benefit. To be of value, screening must detect disease earlier, and treatment of earlier disease must yield a better outcome than treatment at the onset of symptoms [3]."

   Since the abandonment of widespread chest radiography, x-ray mammography has become the most important screening method involving radiologists. Mammography requires dedicated equipment and well-trained staff. Quality control is of the utmost importance, even more so than with other imaging techniques. Acquiring the discernment necessary for image reading and assessment takes a long time and requires studying tens of thousands of images. Radiologists trained for mammography screening read more than 100 images per hour, a strenuous and boring task. The appeal of replacing human image readers with computers that analyze digital mammographic images is therefore easy to understand.

Yet controversy continues to surround screening mammography, particularly for women 40 to 49 years of age. A paper on this topic, based on work at the Cochrane Institute at Copenhagen University, was published in The Lancet in October 2001. The abstract reads as follows:

“In 2000, we reported that there is no reliable evidence that screening for breast cancer reduces mortality. As we discuss here, a Cochrane review has now confirmed and strengthened our previous findings. The review also shows that breast cancer mortality is a misleading outcome measure. Finally, we use data supplemental to those in the Cochrane review to show that screening leads to more aggressive treatment [4]."

In a detailed overview, the authors draw the following conclusion:

“The currently available reliable evidence does not show a survival benefit of mass screening for breast cancer (and the evidence is inconclusive for breast cancer mortality). Women, clinicians, and policy makers should consider these findings carefully when they decide whether or not to attend or support screening programs [5]."

For most people, screening mammography is a solid, indisputable technique. For them, a statement like that above is blasphemy. If you look, for instance, at a review paper in Radiology, you are confronted with a completely different picture:

“Since 1965, breast imaging has become an established radiologic subspecialty that accounts for at least 10% of all examinations performed by radiologists. Indeed, mammography now is the most common imaging examination that directly results in the reduction of mortality from disease [6]."

The outcome of screening studies must be positive. How could there be a negative outcome if all we want is to help?

Now, whom do you believe (“you” being a radiologist, a referring medical doctor, a journalist, or a woman who is dependent on professional advice)?

In general, little notice is taken of the results of epidemiological studies. Since screening is considered beneficial for the population as a whole, results of large-scale screening studies are assessed with a biased view: The outcome must be positive. How could there be a negative outcome if all we want is to help?

Ill-conceived schemes can turn into ideological crusades.

   Public health screening policies, when not based on solid foundations, can easily become an ideological crusade that costs psychological stress, bodily harm, and money. These policies can even ruin more lives than they are designed to save. In particular, mass media reporting gives an extremely biased view of mammography's potential. Researchers from the University of Oxford in the U.K. examined how screening mammography had been reported in six high-circulation U.S. newspapers. Having assessed more than 100 articles published between 1990 and 1997, they concluded:

“Newspapers tended to overrepresent support for screening mammography for women aged 40 to 49 years. Reports would have been improved by identification of all sources for information cited. Medical journalism may benefit from identification of standards similar to those used for reporting medical research [7]."

Newspaper reporters will not write learned papers with references. This is not their task. In-depth scientific articles do not sell mass-circulation newspapers. On the other hand, a woman who is to undergo mammography screening needs clear, straight, and reliable advice: Will screening mammography help to protect me?

It is neither my business nor my intention to bless or damn screening, in this particular case x-ray mammography. I believe that screening in general is an important and necessary task for medical professionals. Some screening methods, however, are much more useful than others and show clear benefits. In the case of widespread use of mammography, there are doubts if this reduces death rates from cancer, according to the review from Copenhagen. Subsequent publications have cast doubts on the Danish group's analysis, adding to the confusion.

A critical approach is necessary. Two points should never be forgotten: The screening procedure must have a clear advantage for the person screened, and the population must not be left in doubt about its reliability. If these philosophies are not adhered to, the public will lose faith in the screening test and in the people proposing and performing it.

It should be clear to everybody involved what the benefits and risks are, because if you find cancer (or something that looks like cancer), you are likely to treat it. The treatment itself may incapacitate or even kill the patient. Depending on the circumstances, cancer might not be the final cause of death, but just a part of aging. Many people live unknowingly with cancers and die of other causes.

While cancer screening is generally increasing in the U.S., take-up is relatively low among groups that lack health insurance or another source of care [8]. Some new examination techniques, such as spiral chest CT for screening lung cancer, are being marketed in the U.S. before benefits have been assessed in strict outcomes studies. Money makes the world go round. Enough people will pay for such an examination because they are afraid of early death, and perhaps their money will lead to more medical progress.

References

1. Ninth Report of the World Health Organization (WHO) Expert Committee on Tuberculosis. Geneva: WHO, 1974.
2. Connelly MT, Inui TS. Principles of disease prevention. In: Braunwald E, Hauser SL, Fauci AS, et al, eds. Harrison's principles of internal medicine. 14th ed. New York: McGraw-Hill, 1998:46-48.
3. Brawley OW, Kramer BS. Prevention and early detection of cancer. In: Braunwald E, Hauser SL, Fauci AS, et al, eds. Harrison's principles of internal medicine. 14th ed. New York: McGraw-Hill, 1998:499-505.
4. Olsen O, Gotzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001;358:1340-1342.
5. Olsen O, Gotzsche PC. Screening for breast cancer with mammography (Cochrane Review). Cochrane Database Syst Rev 2001;4:CD001877.
6. Sickles EA. Breast imaging: from 1965 to the present. Radiology 2000;215:1-16.
7. Wells J, Marshall P, Crawley B, Dickersin K. Newspaper reporting of screening mammography. Ann Intern Med 2001;135:1029-1037.
8. Breen N, Wagener DK, Brown ML, et al. Progress in cancer screening over a decade: results of cancer screening from the 1987, 1992, and 1998 national health interview surveys. J Natl Cancer Inst 2001;93:1704-1713.

Citation: Rinck PA. Screening programs must show clear benefits. Rinckside 2002; 13,2: 5-7.

A digest version of this column was published as:
Screening programs must show clear benefits.
Diagnostic Imaging Europe. 2002; 18,5: 12-14.