A recent Swedish trial that concluded after a period of three decades reiterates the potential benefit of mammographic screening in reducing breast cancer-specific mortality. The study, published in the recent issue of the journal Radiology, provides evidence to support the recommendation for periodic mammography screening in order to reduce the mortality associated with breast cancer.
László Tabár from the Department of Mammography, Falun Central Hospital, Sweden, and co-researchers, investigated the long-term absolute and relative effects of mammographic screening on breast cancer mortality rates. The study, supported by the Swedish National Board of Health and Welfare, evaluated 133,065 subjects aged between 40 and 74 years. Women invited to undergo one-view mammographic screening constituted the study group and those receiving usual care formed the controls. The researchers determined the case status and cause of death with the help of local trial end point committees and an external committee (independently). Negative binomial regression was utilized for mortality analysis.
A substantial reduction in breast cancer-related mortality rate was noted in subjects invited for mammographic screening, based on both local end point committee data (RR=0.69; 95% CI=0.56-0.84; P<0.0001) and external committee consensus data (RR=0.73; 95% CI=0.59-0.89; P=0.002). As per the 29-year follow-up, the number of patients required to undergo the imaging examination for 7 years, noted by the local data and consensus data, to prevent one breast cancer death were 414 and 519, respectively. The study findings estimated that the most prevented deaths due to breast cancer would have occurred following the first 10 years of follow up, without the screening. The researchers noted an increase in the observed number of breast cancer deaths prevented with longer follow up time. They also reiterated the need for long-term evaluation exceeding 20 years to clearly elucidate the absolute benefit of screening.
Similar findings were reported in a case-referent study by Schoor et al (British Journal of Cancer, 2011), which investigated the effect of mammographic screening on breast cancer mortality during the period 1975-2008. A total of 282 deaths due to the malignancy were reported; and 1,410 referents, aged 50 to 69 years, from the total population (n=55,529) were invited to undergo screening. The study results showed that the rate of breast cancer death was 35% lower among the screened patients when compared to the unscreened group (OR=0.65; 95% CI=0.49–0.87). Analysis based on the calendar year demonstrated a substantial reduction in breast cancer mortality from 28% during 1975-1991 to 65% for the period 1992-2008, denoting the increased effectiveness of the screening.
As per the American Cancer Society guidelines (CA A Cancer Journal for Clinicians, 2010), early detection of breast cancer in average-risk individuals involves a combination of regular clinical breast examination and counseling to enhance the awareness of breast symptoms from the age of 20 years, and annual mammography starting at 40 years of age. The guidelines suggest continued screening as long as the individual is in good health and if the risk of becoming a candidate for breast cancer treatment is high. There are no specifications on the upper age limit for discontinuation of the mammography screening; however, the decision on cessation should be personalized based on the benefits and risks of the technique, while considering the estimated life expectancy and general health status of the individual.
Despite years of research and a number of consensus by diverse international organizations, guidelines on the use of mammography for screening breast cancer among women between 40 to 49 years is a matter of debate. A recent study by Schousboe et al (Annals of Internal Medicine, 2011) reported mammography as an expensive technique, considering the cost attributed to the detection of nonprogressive and nonlethal invasive cancer, and the lack of usefulness of false-positive results. The researchers also reiterated the need for individualizing the mammography screening, based on the history of breast biopsy, woman’s age, family history of malignancy, breast density, and perspectives on the potential benefits and limitations of screening.
1. Tabár L, Vitak B, Chen TH, et al. Swedish Two-County Trial: Impact of Mammographic Screening on Breast Cancer Mortality during 3 Decades. Radiology. 2011 Sep;260(3):658-63.
2. van Schoor G, Moss SM, Otten JD, et al. Increasingly strong reduction in breast cancer mortality due to screening. Br J Cancer. 2011 Mar 15;104(6):910-4.
3. Smith RA, Cokkinides V, Brooks D, Saslow D, Brawley OW. Cancer screening in the United States, 2011: A review of current American Cancer Society guidelines and issues in cancer screening. CA Cancer J Clin. 2010 Mar-Apr;60(2):99-119.
4. Schousboe JT, Kerlikowske K, Loh A, Cummings SR. Personalizing mammography by breast density and other risk factors for breast cancer: analysis of health benefits and cost-effectiveness. Ann Intern Med. 2011 Jul 5;155(1):10-20.