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Invasive breast cancer and breast cancer death after non-screen detected ductal carcinoma in situ

BMJ 2024; 384 doi: https://doi.org/10.1136/bmj.q22 (Published 24 January 2024) Cite this as: BMJ 2024;384:q22

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Invasive breast cancer and breast cancer death after non-screen detected ductal carcinoma in situ

Rapid Response:

Finding all cases: not the goal of cancer screening

Dear Editor

Should we be surprised that breast ductal carcinoma in situ (DCIS) not found through screening conveys a relatively high risk of breast cancer mortality? (1) Not really. By analogy with the higher mortality risk of interval invasive breast cancers - i.e., the cancers detected between screening exams - compared to screen-detected invasive cancers (2), it is expected that screen-detected and non-screen-detected DCIS will have a similar risk contrast. That is the result, at least partly, of the length-time bias. It is also because screen-detected and non-screen-detected cases emerged from different subpopulations.

More importantly, should we consider that breast cancer screening fails because it does not identify these cases? No. The genuine aim of cancer screening is neither to find cases nor to make an early diagnosis; it is to decrease cancer-related mortality (3). Finding more cases, at an early stage, results from screening but is not useful per se (4). Hence, while many screenings, e.g., for thyroid cancer or melanoma, increase the number of identified cases and shift the distribution toward early-stage cancer, they do not reduce cancer mortality - and that is why they are not recommended.

It would be possible, and relatively simple, to increase the number of cases found through screening by increasing the frequency of exams, e.g., from once every two or three years to an annual check. The cost, however, will be a larger number of false positive findings and overdiagnosed cases, without a greater reduction in breast cancer mortality (5).

Arnaud Chiolero, professor of public health, from the Population Health Laboratory (#PopHealthLab), University of Fribourg, Switzerland, and the School of Population and Global Health, McGill University, Montreal, Canada

References
1. Mannu GS, Wang Z, Dodwell D, Broggio J, Charman J, Darby SC. Invasive breast cancer and breast cancer death after non-screen detected ductal carcinoma in situ from 1990 to 2018 in England: population based cohort study. BMJ 2024; 384:e075498.
2. Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: an independent review. Lancet 2012; 380(9855):1778-86.
3. Raffle AE, Gray JM (2019). Screening: evidence and practice. Oxford University Press, USA.
4. McCartney M, Fell G, Finnikin S, Hunt H, McHugh M, Gray M. Why 'case finding' is bad science. J R Soc Med 2020; 113(2):54-58.
5. Welch HG, Prorok PC, O'Malley AJ, Kramer BS. Breast-Cancer Tumor Size, Overdiagnosis, and Mammography Screening Effectiveness. N Engl J Med. 2016; 375(15):1438-1447.

Competing interests: No competing interests

28 January 2024
Arnaud Chiolero
Professor of public health and epidemiologist
Population Health Laboratory (#PopHealthLab), University of Fribourg, Switzerland
Route des Arsenaux 41, Fribourg, Switzerland