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Invasive breast cancer and breast cancer mortality after ductal carcinoma in situ in women attending for breast screening in England, 1988-2014: population based observational cohort study

BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m1570 (Published 27 May 2020) Cite this as: BMJ 2020;369:m1570

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Re: Invasive breast cancer and breast cancer mortality after ductal carcinoma in situ in women attending for breast screening in England, 1988-2014: population based observational cohort study

Dear Editor

Mannu et al compared the risk of dying of breast cancer within twenty years for women with screen-detected DCIS with the risk in the general population.[1] The probability of dying of breast cancer for the DCIS cohort was 1.7 times that of the general population (95%CI 1.52 to 1.90). This is an important comparison, but it underestimates the impact of a diagnosis of DCIS at screening on mortality.

If we were to compare the mortality rate among women with DCIS diagnosed at mammography with the rate for women with a negative mammogram, the hazard ratio would be more extreme. In the SEER data set we compared post-DCIS breast cancer mortality to that of women without breast cancer at the same age, and the hazard ratio was 3.36 (95%CI 3.20 -3.53). [2] If the comparison group were women with a negative mammogram, I suspect the hazard ratio would be even higher. In the National Breast Screening study, of the 4462 women who had an initial negative mammogram, 397 women subsequently died of breast cancer.[3] The 20-year actuarial mortality from breast cancer among those with a negative first mammogram was 0.9%. In the Mannu et al, study the 20 year mortality rate was 3.8% for DCIS patients and was 1.6% for women in the general population.

REFERENCES
1. Mannu GS, Wang Z, Broggio J, Charman J, Cheung S, Kearins O, Dodwell D, Darby SC. Invasive breast cancer and breast cancer mortality after ductal carcinoma in situ in women attending for breast screening in England, 1988-2014: population based observational cohort study. BMJ. 2020 May 27;369:m1570. doi: 10.1136/bmj.m1570. PMID: 32461218; PMCID: PMC7251423.

2. Giannakeas V, Sopik V, Narod SA. Association of a Diagnosis of Ductal Carcinoma In Situ With Death From Breast Cancer. JAMA Netw Open. 2020 Sep 1;3(9):e2017124. doi: 10.1001/jamanetworkopen.2020.17124. PMID: 32936299; PMCID: PMC7495235.

3. Miller AB, Wall C, Baines CJ, Sun P, To T, Narod SA. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ. 2014 Feb 11;348:g366. doi: 10.1136/bmj.g366. PMID: 24519768; PMCID: PMC3921437.

Competing interests: No competing interests

26 October 2020
Steven A Narod
Professor
Dalla Lana School of Public Health
Toronto, Ontario