Breast cancer screening offers few benefits to women over 70, finds study
BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g2333 (Published 25 March 2014) Cite this as: BMJ 2014;348:g2333
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The 25 year Canadian breast screening study, this Dutch study and all other screening programs would seem to have the basics right. The idea of screening is a good idea. You screen school kids for dental caries. You screen automobiles (MOT) for leaks and brakes and dodgy filters. You screen the computer for viruses and Trojan Horses and worms. And so on.
Screening is not the issue. Screening is part of life and it works. It prevents molehills from becoming mountains. The issue is what do you do with the results of screening. Fit new brake pads, use fluoride toothpaste, install antiviral software etc. The process is well founded in virtually all walks of life. The second stage after the decision to screen is what do you look for and how do you look for it.
If you look for the wrong think with the right tools or the right thing with the wrong tools or the wrong thing with the wrong tools ...you get flawed screening. In the area of breast cancer the mammography has to be up to the job, and maybe the next step is the important one. What do you do about what you find. Watchful waiting, re-screening after an interval, intervention when signs of spread appear etc.
When the prevalence of breast cancer is so high. When it affects a disproportionate number of young women. When it is so invasive and serious. You have no option but to screen. If you don't screen you will miss early disease. This seems obvious.
Does screening save lives? It has to. In every other human endeavor screening saves lives. Repaired cars prevent accidents, focussed colonoscopy on risk groups saves lives, lipid and cholesterol screening saves lives par excellence. Breast screening also saves lives and if the statistics don't prove this they are wrong or some aspect of the screening process is wrong!
Screening for breast cancer at age 70 is another issue. If the lifetime prevalence of breast cancer in UK is that 1 in 8 women will get the disease it is unconscionable not to screen.
Competing interests: No competing interests
Re: Breast cancer screening offers few benefits to women over 70, finds study
Quit often, studies have shown contrasting results about the benefits of early detection of breast cancer by screening. Mammography has been the choice of screening method with varying degrees of sensitivity. Sensitivity variations occur due to several factors,s one of them being density of the breast tissue. It has been seen that lower age group women are more likely to have dense breast tissue leading to lesser chances of detection of breast cancer at an early stage with precision and chances of early detection increases with increasing age of the women due to lesser density of breast. Available report showed 30-55% detection rate of breast cancer by mammography in breast with high tissue density (1-2). Better contrast of breast tissue with digital mammography yields better detection rate upto 70% (2). Although MRI yields better detection rate than mammography, its use in screening is limited because of the cost, availability, accessibility especially in resource poor countries.
It has been reported that expected benefits in terms of saving lives related to annual mammographic screening in women aged 40 to 49 years is 36%, 46% for age group 50-59 years and 44% for 60-69 years old women; with biennial screening 39% lives could be saved among women aged 50 to 69 years as compared to only 18% in younger women aged 40-49 years (3).
In resource poor countries where mammography is still limited to big hospitals in the urban areas, a large number of women cannot be benefitted by mammography. In such a situation, the best possible way to detect breast cancer is by promotion of breast self examination (BSE). However, due to associated problems with BSE such as anxiety, depression (4), more detection of benign tumors with more intervention in the form of biopsy, BSE has not been recommended for breast cancer screening. It has been reported that the median size of breast lump that can be detected by BSE ranges between 2-2.5 cms which may be associated with early stage of breast cancer and also at an advanced stage. A large study reported that there are equal chances of deaths due to breast cancer in those who performed BSE and those who did not perform BSE (5).
Considering the fact that natural history of breast cancer does not change after detection, a group of researchers opine that screening does not increase the survival duration of the breast cancer patients since early detection leads to a false sense of increasing the survival period which is often termed as ‘lead time bias’. In other words, if a woman survives upto 50 years after detection at 40 years, she would be living for 10 years, while if a woman gets breast cancer detected at 45 years, she would still be surviving till 50 years with treatment showing that early detection does not alter the survivality duration. Under these circumstances, can screening be truly beneficial ?
Early Randomized clinical trials(RCT) have shown benefits of mammography as a screening and the 2002 report of the United Services Preventive Services Task Force (USPSTF)(6) based on the RCTs showed a summary relative risk (RR) of death of 0.84 (95% confidence interval of 0.77 to 0.91) i.e. an estimated 16% decrease in breast cancer deaths with mammography. RCTs are not free from bias specially participation bias in which lesser women participate in trial and the other non participants may adopt screening methods for early detection for breast cancer (contamination) which may adversely affect the study results. In such a situation, the reported benefits of mammography may be “underestimated”.
Despite conflicting results from studies on the benefits of screening for breast cancer, it seems reasonable to assume that if detected in an early stage, breast cancer patient survival rate increases which may be 100% in stage 0 to stage I. Hence, let us not be carried away with varying reports of studies on the controversial role of screening in breast cancer and optimistically stick to the age old concept that early detection leads to better survival in breast cancer patients.
References
1. Mandelson MT, Oestreicher N, Porter PL, et al. Breast density as a predictor of mammographic detection: comparison of interval- and screen-detected cancers. J Natl Cancer Inst 2000;92:1081-1087.
2. Pisano ED, Gatsonis C, Hendrick E, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med 2005;353:1773-1783.
3. Breast-cancer screening with mammography in women aged 40-49 years. Swedish Cancer Society and the Swedish National Board of Health and Welfare. Int J Cancer 1996;68:693-699.
4. Baxter N; Canadian Task Force on Preventive Health Care. Preventive health care, 2001 update: should women be routinely taught breast self-examination to screen for breast cancer?. CMAJ 2001;164 (13): 1837–46.
5. Thomas DB, Gao DL, Ray RM, et al. Randomized trial of breast self-examination in Shanghai: final results. J. Natl. Cancer Inst. 2002;94 (19): 1445–57.
6. Humphrey LL, Helfand M, Chan BK, Woolf SH. Breast cancer screening: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2002;137:347-360.
Competing interests: No competing interests