Overdiagnosis in breast screening is considered by some observers to be the most adverse outcome associated with mammographic screening, but supporters of screening passionately disagree. So, who is right? ECR 2020 delegates will learn more this afternoon, when the latest evidence comes under intense scrutiny.
Defined as the detection of a breast cancer at screening that is histologically confirmed but may not have been clinically diagnosed during the woman’s lifetime, overdiagnosis can occur in anywhere between 1% (Italy) and 10% (U.K.) of cases, according to Prof. Philippe Autier, PhD, vice president of population research, International Prevention Research Institute, Dardilly, France. He claims that one of the harms of breast screening is the number of false positive results, sometimes leading to biopsy procedures, which he claims may ultimately end in mastectomy.
His argument against screening rests on his belief that “the long-term evolution of these lesions (in-situ tumours) is poorly known, and only a minority of in-situ tumours would represent a true precursor of potentially deadly cancer.” Furthermore, Autier claims there is a lack of awareness amongst the radiology community of the harms of over-screening and overdiagnosis, which he says “are real issues”, and he adds that even if some radiologists acknowledge the existence of overdiagnosis, there is often a tendency to minimise its importance.
He argues that the more frequent a screening test, the greater the probability of overdiagnosis. Each additional test, such as ultrasound and MRI, performed on asymptomatic patients increases the probability of false positive findings and of overdiagnosis. Autier points out that overdiagnosis has also been observed in other screening methods, e.g., for prostate cancer (with serum prostate specific antigen), thyroid cancer, skin melanoma, neuroblastoma (with dosage of urine catecholamine), ovarian cancer (with serum CA125 antigen), and lung cancer (low-dose CT).
Ultimately, he says “treating over-diagnosed cancers equates to overtreatment because it is unnecessary – it does not improve a subject’s health or cure a potentially deadly tumour – while it affects quality of life, can be harmful (e.g., unnecessary surgery, radiotherapy, and chemotherapy), and is costly.” He adds that overdiagnosis affects patients who do not benefit from screening, and he considers that overdiagnosis and overtreatment have a considerable negative impact on the harm-to-benefit balance of cancer screening.
At today’s session, Autier’s views will be countered by fellow speaker Dr. Mireille Broeders, Full Professor of Personalised Cancer Screening at the Department for Health Evidence, Radboud UMC, Nijmegen, the Netherlands.
“It is essential to realise that some overdiagnosis is inherent in most screening, and therefore, also in breast cancer screening,” she told ECR Today. “In trying to find early-stage cancers, we will also find some cancers that would never have surfaced clinically in a woman’s life. Unfortunately, clinicians are not able (yet) to determine which cancers detected through screening are really ‘over-diagnosed cancers’ and should not be treated.”
Currently, there is intense effort in research to better characterise both screen-detected and clinically detected cancers and to find markers that will help doctors limit overtreatment. She stresses that when communicating with patients, it is important to explain that most women undergoing screening will not be diagnosed with breast cancer in their lifetimes, and so the risk of being diagnosed with a non-progressive breast cancer is extremely small.
As a scientist, Broeders intends to provide a balanced account of the benefits of screening. “The main benefit of mammographic breast screening is that women who participate in screening have a lower chance of being diagnosed with an advanced breast cancer and therefore a lower chance of dying from breast cancer,” she noted, adding that since women are diagnosed predominantly when they are middle-aged, breast cancer screening is also responsible for a significant number of years of life gained.
Additional benefits of breast screening are that cancers are detected at an earlier stage, meaning treatment can be less intensive, e.g., less extensive surgery, less extensive radiotherapy, and a lower chance of chemotherapy, each of which can have severe side-effects. An early diagnosis will have a positive impact on the quality of life of these women, she believes.
Moreover, the balance of benefits and harms for screening women at average risk is less favourable at a younger age. Screening offered as a public health intervention to women at average risk of breast cancer should not start before the age of 45 and would be most appropriate to start at age 50 for the majority of women, according to Broeders. Unfortunately, attempts to identify ways to reduce the frequency of breast cancer through primary prevention have been discouraging.
Reducing breast cancer mortality through early detection and treatment of the disease, i.e. secondary prevention, is the best way forward, she said. Screening aims to detect breast cancer when it is still asymptomatic and localised to the breast, and it is possible to treat the patient with curative intent, so advancing the time of diagnosis through screening can improve the prognosis of patients.
Looking to the future, Broeders talks about the importance of risk-based screening regimens, which she said can potentially make screening for breast cancer more effective and efficient by targeting women at higher risk and are most likely to benefit, while reducing exposure in women at lower risk and who are more likely to experience the harms.
Artificial intelligence (AI) can help improve personalised screening regimens and the performance of screening radiologists. AI can help show that the mammograms contain much more information than the radiologist can see, and using modelling techniques, harm-benefit ratios and cost-effectiveness of personalised risk-based screening strategies can be estimated. However, it is essential to understand the opinions of women invited for screening and to provide insights on the acceptability, ethical, legal, and organisational implications of personalised strategies, before implementation is considered, she noted.
“Breast cancer screening is a well-balanced healthcare intervention for the population invited. Arguments that it is unproven, or that harms exceed benefits, are made by individuals, not expert groups,” she said, though she admits that just like in any field of medicine, there is scope to improve the balance between benefits and harms that can include offering screening risk-based and optimising screening strategies using AI.
Ultimately, she thinks every woman should be enabled to make a well-informed individual choice on whether to attend breast cancer screening or not.
Pros & Cons Session
PS 427 Breast cancer: to screen or not to screen?
- A. The evidence for breast screening
Mireille Broeders; Nijmegen/NL
- B. The evidence against breast screening
Philippe Autier; Dardilly/FR
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