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Originally published as JCO Early Release 10.1200/JCO.2008.17.9374 on December 15 2008 © 2009 American Society of Clinical Oncology.
Mammography Screening Among Women Age 80 Years and Older: Consider the RisksDivision of General Medicine and Primary Care, Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA To the Editor: Despite the authors' enthusiasm for mammography screening among women age 80 years and older,1 we caution readers from using these data to screen these women blindly without considering life expectancy. Although this study demonstrates that regular mammography screening among women age 80 years and older is associated with smaller tumors and earlier stage breast cancer at diagnosis, these findings are not surprising. Observational studies evaluating a screening test will show that those who are screened are diagnosed with smaller tumors than those who are not screened due to selection bias, lead time bias, and length time bias.2 Selection bias was present in this study, given that the women who underwent screening were healthier than those who were not screened, and we would expect these women to live longer. In fact, the authors found that mammography screening was associated with a protective effect even among noncancer deaths. Lead time bias occurs because screening tests can advance detection of disease but may not prolong survival. Therefore, it is essential to consider lead time bias when comparing cancer-specific survival of screened and unscreened populations. Although previous studies that used observational data to examine benefits of mammography screening among older women attempted to account for lead time bias, this study did not address this issue at all.3 When lead time was considered in the previous study, regular mammography screening was not associated with a significant mortality benefit for women age 85 years and older.3 Length time bias refers to the fact that slower-growing tumors are more likely to be detected by screening than faster-growing, more aggressive tumors. Therefore, women with screen-detected tumors are likely to have a better prognosis than those detected clinically. Perhaps most importantly, this study addressed the potential benefits of screening without considering any of the risks. One important risk of screening, particularly for older women, is overdiagnosis; that is, finding and treating breast cancers that would have never become clinically significant during a woman's lifetime.4 This study excluded women with carcinoma in situ, yet most experts would agree that detection of ductal carcinoma in situ in women age 80 years and older likely represents overdiagnosis, given that ductal carcinoma in situ is unlikely to progress to invasive breast cancer in the lifetime of a woman age 80 years and older.5,6 The authors report that the number of women age 80 years and older diagnosed with breast cancer nearly tripled from 1996 to 2002; however, deaths from breast cancer among women in this age group did not triple during the same period, further suggesting that some of the tumors diagnosed represent clinically insignificant disease.7 Although the incidence of breast cancer increases until age 80, the proportion of women with breast cancer who die of breast cancer declines with advancing age.8 Older women with breast cancer who have at least two comorbidities are 20 times more likely to die of their comorbid disease than their breast cancer.9 In the general population, fewer than 2% of women age 80 years and older die of breast cancer.10 This study also showed that the majority of women with breast cancer died from causes other than their breast cancer. In addition, this study examined a healthier population of women age 80 years and older by excluding women with a history of other cancers and those whose tumors were unstaged or not histologically confirmed. Studies have found that older women with greater comorbidity are less likely to have their tumors staged or biopsied.11 In addition, some of the observed survival difference between the screened and unscreened women may be associated with differences in treatment. The authors report that receipt of breast-conserving surgery and radiotherapy was associated with more frequent mammograms. We agree with the authors that a randomized controlled trial would be the best way to determine whether mammography screening results in a mortality benefit for women age 80 years and older. However, we also agree that such a trial is unlikely, given the substantial costs. In the meantime, the authors recommend that the benefits of screening be discussed with women age 80 years and older. We, as well as the 2005 American Geriatrics Society Clinical Practice Committee, recommend that clinicians discuss both the potential benefits and risks of mammography screening with women age 80 years and older, and that screening be targeted to older women with a life expectancy of at least 5 years.12 It was reassuring that this study found that older women who had greater comorbidity scores were less likely to undergo screening. Although the authors called this a potential bias, we would consider this appropriate care and an indication that mammography among women age 80 years and older is being targeted to healthier women with longer life expectancies. In fact, nationally, only 50% of women age 85 to 89 years and 25% of women age 90 years and older have life expectancies of 5 years.4 Because the authors found that the proportions of women in each of these age groups being screened were similar to the proportion of women in these age groups with life expectancies long enough to potentially benefit, these data may suggest that screening rates may be already at appropriate levels. Mammography screening may result in earlier detection for some women age 80 years and older; however, it is still unclear the extent to which women age 80 years and older derive a mortality benefit from breast cancer screening or the extent to which screening results in overdetection and overtreatment for these women. Other significant and commonly cited risks of screening such as false-positive and false-negative tests should be also considered, as well as patient preferences.4 We previously examined preferences around mammography screening in women age 80 years and older and found that although some have strong opinions about whether or not they should undergo screening, the majority are influenced by their physician's recommendation.13,14 However, physicians noted that they found it challenging to make recommendations about mammography screening for women age 80 years and older because of the limited data available on the benefits and risks.12 More data are needed on both the benefits and risks of screening women age 80 years and older and the benefits and risks of treatment to inform screening decisions. AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The author(s) indicated no potential conflicts of interest. REFERENCES
1. Badgwell BD, Giordano SH, Duan ZZ, et al: Mammography before diagnosis among women age 80 years and older with breast cancer. J Clin Oncol 26:1–7, 2008. 2. Rothman KJ. Epidemiology: An introduction. Oxford, United Kingdom: Oxford University Press, 2002. p.96–98, 203–204. 3. McCarthy EP, Burns RB, Freund KM, et al: Mammography use, breast cancer stage at diagnosis, and survival among older women. J Am Geriatr Soc 48:1226–1233, 2000.[Medline] 4. Walter LC, Covinsky KE: Cancer screening in elderly patients: A framework for individualized decision making. JAMA 285:2750–2756, 2001. 5. Ernster VL, Ballard-Barbash R, Barlow WE, et al: Detection of ductal carcinoma in situ in women undergoing screening mammography. J Natl Cancer Inst 94:1546–1554, 2002. 6. Weir HK, Thun MJ, Hankey BF, et al: Annual report to the nation on the status of cancer, 1975-2000, featuring the uses of surveillance data for cancer prevention and control. J Natl Cancer Inst 95:1276–1299, 2003. 7. Page DL, Dupont WD, Rogers LW, et al: Continued local recurrence of carcinoma 15-25 years after a diagnosis of low grade ductal carcinoma in situ of the breast treated only by biopsy. Cancer 76:1197–1200, 1995.[CrossRef][Medline] 8. Diab SG, Elledge RM, Clark GM: Tumor characteristics and clinical outcome of elderly women with breast cancer. J Natl Cancer Inst 92:550–556, 2000. 9. Satariano WA, Ragland DR: The effect of comorbidity on 3-year survival of women with primary breast cancer. Ann Intern Med 120:104–110, 1994. 10. Woloshin S, Schwartz LM, Welch HG: Risk charts: Putting cancer in context. J Natl Cancer Inst 94:799–804, 2002. 11. Bouchardy C, Rapiti E, Fioretta G, et al: Undertreatment strongly decreases prognosis of breast cancer in elderly women. J Clin Oncol 21:3580–3587, 2003. 12. American Geriatrics Society. Breast cancer screening in older women. http://www.americangeriatrics.org/products/positionpapers/breast_cancer_position_statement.pdf. 13. Schonberg MA, Ramanan RA, McCarthy EP, et al: Decision-making and counseling around mammography screening for women aged 80 or older. J Gen Int Med 21:979–985, 2006.[CrossRef][Medline] 14. Schonberg MA, McCarthy EP, York M, et al: Factors influencing elderly women's mammography screening decisions: Implications for counseling. BMC Geriatr 7:26; 2007.[CrossRef][Medline]
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Copyright © 2009 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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