In 2001, a Cochrane systematic review by Olsen & Gøtzsche [Ref] concluded that ‘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). In 2013 Swiss Medical Board recommended abolishing the existing breast screening programs[Ref]. The breast screening guidelines published by the Ministry of Health (MoH) in 2014 [Ref] gives a rational evidence-based view which is valid even currently. However, in 2018 November the MoH called an expert group meeting to plan an islandwide breast screen program with the help of mobile units. One of the main reasons given for this step is the increasing incidence of breast cancer in the younger females over the past decade.
What is screening?
Epidemiology is about the understanding the distribution and determinants of diseases. With regards to determinants of diseases, the goal is to prevent the development of disease in a healthy persons. If prevention is difficult the next option is screening for ‘early detection of diseases’ in the asymptomatic stage [Fig 1].
Screening refers to the application of a test to people who are yet asymptomatic for the purpose of classifying them with respect to their likelihood of having a particular disease. The screening test itself does not diagnose illness. Those who test positive are sent on for further evaluation by a subsequent diagnostic test or procedure to determine whether they do in fact have a disease. However even the basic assumption that early treatment will improve prognosis is not true in all circumstances. [Ref Epidemiology in Medicine -Henniken]
An implicit assumption underlying the concept of screening is that early detection, before the development of symptoms will lead to more favourable prognosis. The explanation is that treatment began before the disease becomes clinically manifest will be more effective than later treatment. However this may not happen as anticipated. For example the PSA screening test identifies prostate cancer early, but fail to make a difference on the mortality rate because of the long lead-time bias.
Screening for breast cancer
Screening has worked well has been attributed for many preventative initiatives of modern medical practice. However this has been under intense scrutiny during the past decade. One of the first focus has been breast cancer screening. The history of breast cancer screening goes back to more than two decades and the first national study in Canada was published in 1992 [ Ref ] that concluded that, ‘Screening with yearly mammography and physical examination of the breasts detected considerably more node-negative, small tumours than usual care, but it had no impact on the rate of death from breast cancer up to 7 years’ follow-up from entry.’
In 2001 a Cochrane meta-analysis of RCTs reported that mammography screening reduces breast cancer related mortality by 15% and that one in three cancers are overdiagnosed [Ref -Gotzscher 2013]. An an update of a Canadian trial that found no effect of mammography screening on breast cancer mortality at a cost of 22% overdiagnosis of cancer [Ref -Miller]. The Dutch screening programme reports that finds at most a 5% reduction in breast cancer related mortality and overdiagnosis in one out of three cancers detected [Ref ].
‘We are still nudging women to attend mammography screening. It is likely that many women and their clinicians are not fully informed about the true balance of risks and benefits.10 The good news is that breast cancer related mortality is falling. The bad news is that screening mammograms are unlikely to be responsible for that benefit, while causing well documented harm.’ [Ref – BMJ Editorial Kalanger 2017]
Screening for breast cancer with mammography – Cochrane Reviews
One of the first Cochrane systematic reviews published in 2001 by Olsen & Gøtzsche [Ref] stated that ‘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.’
The 2013 updated Cochrane review states [Ref ] that ‘If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings. To help ensure that the women are fully informed before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.’
Mammography screening: A major issue in medicine [Ref European Journal of Cancer – France]
- After 20–30 years of mammography screening, the incidence rates of advanced and metastatic breast cancer have remained stable.
- Breast cancer mortality rates have not decreased more rapidly in areas where mammography is in place since the late 1980s.
- One third to one half of mammography-detected breast cancers would not have been clinical during lifetime (overdiagnosis).
- Breast screening randomised trials have adopted distinctive methods that led to exaggerating the efficacy of screening.
- The influence mammography screening may have on mortality decreases with the increasing efficiency of cancer therapies.
- The comparison of the performance of different screening modalities – e.g. mammography, digital mammography, ultrasonography, magnetic resonance imaging (MRI), three-dimensional tomosynthesis (TDT) – concentrates on detection rates, which is the ability of a technique to detect more cancers than other techniques. However, a greater detection rate tells little about the capacity to prevent interval and advanced cancers and could just reflect additional overdiagnosis. Studies based on the incidence of advanced cancers and on the evaluation of overdiagnosis should be conducted before marketing new breast-imaging technologies.
USPTF Breast Cancer: Screening 2016
|Women aged 50 to 74 years||The USPSTF recommends biennial screening mammography for women aged 50 to 74 years.||B|
|Women aged 40 to 49 years||The decision to start screening mammography in women prior to age 50 years should be an individual one. Women who place a higher value on the potential benefit than the potential harms may choose to begin biennial screening between the ages of 40 and 49 years.
• For women who are at average risk for breast cancer, most of the benefit of mammography results from biennial screening during ages 50 to 74 years. Of all of the age groups, women aged 60 to 69 years are most likely to avoid breast cancer death through mammography screening. While screening mammography in women aged 40 to 49 years may reduce the risk for breast cancer death, the number of deaths averted is smaller than that in older women and the number of false-positive results and unnecessary biopsies is larger. The balance of benefits and harms is likely to improve as women move from their early to late 40s.
• In addition to false-positive results and unnecessary biopsies, all women undergoing regular screening mammography are at risk for the diagnosis and treatment of noninvasive and invasive breast cancer that would otherwise not have become a threat to their health, or even apparent, during their lifetime (known as “overdiagnosis”). Beginning mammography screening at a younger age and screening more frequently may increase the risk for overdiagnosis and subsequent overtreatment.
• Women with a parent, sibling, or child with breast cancer are at higher risk for breast cancer and thus may benefit more than average-risk women from beginning screening in their 40s.
Go to the Clinical Considerations section for information on implementation of the C recommendation.
|Women aged 75 years or older||The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening mammography in women aged 75 years or older.||I|
National Cancer Control Sri Lanka 2014 [Ref]