Mammography for older women?

Abstract

Aging HealthVol. 9, No. 4 EditorialFree AccessMammography for older women?Anthony B MillerAnthony B Miller* Author for correspondenceDalla Lana School of Public Health, University of Toronto, Cananda. Search for more papers by this authorEmail the corresponding author at ab.miller@sympatico.caPublished Online:5 Aug 2013https://doi.org/10.2217/ahe.13.23AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInReddit Keywords: breastcancermammographyolder womenscreeningThose participating in the recent controversies as to whether mammography screening every 2 years is adequate in women over the age of 50 years, engendered by the latest (2009) recommendations of the US Preventive Services Task Force on breast screening, have overlooked several issues [1]. One is that the Swedish Two-County trial, the screening trial most often cited as showing a major impact of mammography screening on breast cancer mortality, did not use annual mammography in women over the age of 50 years, but instead used mammography every 33 months [2]. As a result, in Europe, the majority of the breast screening programs only offer mammography every 2 or 3 years. Indeed, in the UK, when discussions were ongoing about whether to screen annually rather than every 3 years, a trial was commissioned to specifically evaluate the issue. The result was a clear indication that it would not be cost effective to move from 3-yearly to annual screening [3]. Therefore, in the UK, the basic screening policy is still to offer mammography every 3 years to women aged 50–69 years. Part of the reason for the fixation on annual screening in the USA has been the tradition to offer women annual Pap smears to check for the precursors of cancer of the cervix, a policy that has now been shown to be unnecessary and wasteful in terms of resources [4]. Another issue is that the Swedish Two-County trial was based on randomization in groups (clusters), not individually, with no contact with the women in the control group until the end of screening in the study group. Therefore, it has not been possible to produce data that convincingly show that the compared groups were well balanced initially. Furthermore, the fact that all-cause mortality was identical in the compared groups (the lower breast cancer mortality in the screened group being balanced by higher all-cause, other than breast cancer, mortality) suggests problems in ascertaining the cause of death [5]. This has been called the ‘slippery linkage’ bias, a bias whereby deaths that follow from evaluation of a positive screening test, for example deaths due to treatment of a detected abnormality, are attributed to causes other than the outcome being evaluated, in this case death due to breast cancer. Therefore, there is room for doubt that the mortality differences in the Swedish Two-County trial are due to mammography screening, rather than other unmeasured differences between the groups.However, perhaps most critical is the fact that improvements in the treatment of breast cancer in the last two decades [6], combined with major reductions in the size of breast cancer normally detected by women themselves, have largely made the early breast screening trials irrelevant to policy today.The Swedish breast screening trials, in which a benefit from mammography screening in women over the age of 50 years was found, were conducted in an era prior to the advances in breast cancer treatment and with breast cancers detected at larger sizes than in the only trial specifically designed to evaluate the benefit from mammography screening over and above that of good breast examinations [7]. The trial was conducted with the benefit of improved breast cancer treatment, introduced in Canada in the early 1980s, with smaller breast cancer sizes documented in the control group when compared with the Swedish Two-County trial [8], and with mammography that complied with, or exceeded, the standards in other trials [9]. Both groups had good breast examinations annually, in addition to annual mammography in the intervention group, which resulted in no benefit.What has often been overlooked is that the trials that used randomized invitations to screening, not only failed to identify the controls, but many aspects concerned with breast awareness and treatment were available to the screen detected but not to the controls. Therefore, it is notable that the Canadian trial [7], which used individual randomization after consent, failed to find any benefit from mammography screening as these nonscreening factors that impact upon breast cancer mortality were applied similarly to the cases in the compared arms.The major reductions in breast cancer mortality since 1990 in the USA and other countries has been attributed, by many, to the effect of mammography screening applied in the population [10,11]. However, the declines in breast cancer mortality do not relate temporally to the introduction of mammography screening, but instead to the introduction of improved therapy for breast cancer [12]. When the death rates for breast cancer are evaluated by age group, it is found that the major declines have occurred in younger women and that there has been far less decline in women aged 70–79 years compared with women aged 50–59 or 60–69 years, and a delayed decline has occurred for women aged 80–89 years [13]. It is important to recognize that if screening is offered to women aged 65 years or more, there is bound to be at least a 5-year lag before any impact on breast cancer deaths can be expected. The adverse effects of screening, which include the false-positive detections, the unnecessary investigations and biopsies, and the detection of breast cancers that would never have presented in that woman’s lifetime (overdiagnosis), are seen immediately. It has been estimated that overdiagnosis as a result of mammography screening has affected 1.3 million US women in the past 30 years and that approximately 30% of breast cancers detected by mammography screening are overdiagnosed [14]. It has also been noted that the introduction of screening in the USA was associated with a doubling in the number of cases of early-stage breast cancer detected each year, from 112 to 234 cases per 100,000 women – an absolute increase of 122 cases per 100,000 women – but the rate at which women present with late-stage cancer decreased by only eight cases per 100,000 women [14]. Such a small decrease in late-stage disease suggests that mammography screening was having little impact upon breast cancer mortality, but considerably increased the extent to which breast cancer became a clinical problem.Breast cancer has a long natural history. Most deaths from breast cancer in women older than 65 years will occur in those whose breast cancers were diagnosed under the age of 65 years. Therefore, these deaths cannot be influenced by screening in women over the age of 65 years. Furthermore, women aged 65 years or more, who are interested in screening, will almost invariably have been screened at a younger age and, if breast cancer has not been found up to that point (if it had they would be under surveillance to detect recurrence of breast cancer and would not be eligible for screening), it automatically places them in a low-risk group for breast cancer and for death from the disease.It may be asked; why is it that the majority of women and their physicians are convinced that the detection of an early breast cancer by mammography is beneficial? The main reason is that for decades the American Cancer Society and others have promoted tests for early cancer detection, initially with the Pap smear for cervical cancer screening, then mammography for women aged 40 years or more and, more recently, other tests for colorectal cancer [101]. Others are actively promoting screening for prostate and lung cancer. What has been inadequately explained is that there are major differences between the lesions that are found when screening for cervical and colorectal cancer, and the cancers that are detected by screening for breast, prostate and lung cancer. For cervical and colorectal cancer, cancer precursors are sought, but for the others, it is the cancer itself. When you find and remove a cancer precursor, you prevent the cancer occurring and thus reduce both the incidence and mortality from the disease. Although far more cancer precursors are detected compared with the number of cancers that would eventually occur, their treatment is relatively simple. However, when screening for a cancer itself there are many false-positive findings, treatment tends to be more extensive than for precursors, complications of screening are more likely than when a precursor is detected and there can be no reduction in incidence. In fact, overdiagnosis of cancers in the order of 20–50% will occur and usually there are only small reductions (if any) in cancer mortality. Therefore, the cost, in terms of diagnostic tests and overdiagnosis, is high and the eventual benefit small.We need to change our strategy towards breast cancer. One of the most modifiable risk factors for breast cancer is obesity, with an effect maximal in post-menopausal women [15]. Prevention of obesity, which includes promotion of physical activity, needs to achieve far more prominence with regard to its beneficial effect in lowering the incidence of breast cancer in older women. Furthermore, we need to ensure that older women understand that breast cancer can occur throughout life and they should be encouraged to ensure that if there are changes in their breasts, an investigation is initiated to exclude cancer. Breast cancer has ‘come out of the closet’ in younger women; however, the same is still needed in older women. Mammography should continue to maintain prominence as a diagnostic technique, rather than screening; in practice, this is the role that mammography was originally intended to have.Financial & competing interests disclosureThe author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript.References1 US Preventive Services Task Force. Screening for breast cancer: U.S. Preventive Services Task Force recommendation statement. Ann. Intern. Med.151(10),716–726 (2009).Crossref, Medline, Google Scholar2 Tabár L, Fagerberg G, Duffy SW, Day NE, Gad A, Grontoft O. 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International Agency for Research on Cancer, Press, Lyon, France (2002).Google Scholar101 American Cancer Society guidelines for the early detection of cancer. www.cancer.org/healthy/findcancerearly/cancerscreeningguidelines/american-cancer-society-guidelines-for-the-early-detection-of-cancer (Accessed 2 April 2013)Google ScholarFiguresReferencesRelatedDetails Vol. 9, No. 4 Follow us on social media for the latest updates Metrics History Published online 5 August 2013 Published in print August 2013 Information© Future Medicine LtdKeywordsbreastcancermammographyolder womenscreeningFinancial & competing interests disclosureThe author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript.PDF download